Limb-Girdle Muscular Dystrophies

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MUSCULAR DYSTROPHY SYNDROMES ^²

Limb Girdle Dystrophies
Dominant (LGMDD)
1: DNAJB6; 7q36
2: TNPO3; 7q32
3: HNRPDL; 4q21
4: Calpain-3; 15q15
5 (Bethlem 1)
COL6A1: 21q22
COL6A2: 21q22
COL6A3: 2q37
Previous classification
Myopathies, Dominant
1H: 3p23
Ankle contractures & High CK
Bethlem 2: COL12A1; 6q13
Central core: RYR1; 19q13
Cytoplasmic body
Distal myopathies
MPD2: MATR3; 5q31
Emery-Dreifuss
Lamin A/C; 1q21
SYNE1; 6q25
SYNE2; 14q23
Facioscapulohumeral
1A: DUX4; 4q35
1B: DUX4; 10qter
2: SMCHD1; 18p11
Myofibrillar (Desmin storage)
Myosin storage: MYH7; 14q11
Myotonic (DM1): DMPK; 19q13
Myotonic (DM2): ZNF9; 3q21
Oculopharyngeal: PABP2; 14q11

Limb Girdle Dystrophies
Recessive (LGMDR)
1 (2A): Calpain-3; 15q15
2 (2B): Dysferlin; 2p13
3 (2D): α-Sarcoglycan; 17q21
4 (2E): β-Sarcoglycan; 4q12
5 (2C): γ-Sarcoglycan; 13q12
6 (2F): δ-Sarcoglycan; 5q33
7 (2G): Telethonin; 17q12
8 (2H): TRIM32; 9q33
9 (2I; MDDGC5): FKRP; 19q13
10 (2J): Titin; 2q24
11 (2K; MDDGC1): POMT1; 9q34
12 (2L): ANO5; 11p14
13 (2M; MDDGC4): Fukutin; 9q31
14 (2N;MDDGC2): POMT2; 14q24
15 (2O; MDDGC3): POMGnT1; 1p32
16 (2P; MDDGC9): DAG1; 3p21
17 (2Q): Plectin 1f; 8q24
18 (2S): TRAPPC11; 4q35
19 (2T): GMPPB; 3p21
20 (2U): ISPD; 7p21
21 (2Z): POGLUT1; 3q13
22: COL6A2; 21q22
23: LAMA2; 6q22
24: POMGNT2; 3p22
Other
Pompe (2V): GAA; 17q25
2W: LIMS2; 2q14
2X: POPDC1; 6q21
2Y: TOR1AIP1; 1q25
MDDGC12: POMK; 8p11
Caveolin-3
Merosin (Laminin α2)
23 (Absent): 6q22
Reduced
Abnormal: LGMD 2I
MFM (2R): Desmin; 2q35
PYROXD1: 12p12
Myopathy +
Cardiomyopathy
Arrhythmia: POPDC1; 6q21
Dilated: DPM3; 1q12
Hypertrophic: TRIM63; 1p36
Digenic: + Murf3 heterozygous
Triangle tongue (2W): LIMS2; 2q14
Contractures: TOR1AIP1; 1q25
Epilepsy: DPM2; 9q34
Infant stiffness: CRYAB; 11q22
Lipodystrophy: PTRF; 17q21
MR & Eye (2T): GMPPB; 3p21
Ophthalmoplegia: MYH2; 17p13

Limb Girdle Dystrophies: X-linked
Barth: G4.5 (Tafazzins); Xp28
Becker: Dystrophin; Xp21
Duchenne: Dystrophin; Xp21
Emery-Dreifuss
Emerin; Xq28
FHL1: Xq26
Manifesting carriers
Dystrophinopathy
Myotubularin
McLeod Syndrome: XK; Xp21.1;
Vacuolar
Danon's disease: LAMP-2; Xq24
Excess Autophagy: VMA21; Xq28
MR & Cardiac: LAMP-2; Xq24

LGMD: General features
Muscle pathology

Muscle proteins
Connective tissue
Dystrophin & associated proteins
Intermediate filaments
Neuromuscular junction
Nuclear envelope
Structural & Contractile

DAG complex +

Other inherited myopathy syndromes

α-Dystroglycan disorders (MDDGC)
Aggregates
Cytoplasmic body
Hyaline body: MYH7; 14q11; Dominant
KFS4: MYO18B; 22q12; Recessive
Myofibrillar (Desmin)
Reducing body
Spheroid body (Myotilin)
Tubular
Tubular arrays
VMCQA: CASQ1; 1q23; Dominant
APECED: AIRE; 21q22; Recessive
Autophagy
Excessive: VMA21; Xq28
Multisystem: CLN3; 16p11; Recessive
Other
Barnes myopathy: Dominant
Cardiac + Myopathy
Cardiomyopathy-associated
Cardiomyopathy (? LGMD1B)
LGMD 1E: Desmin; 2q35; Dominant
Congenital
Myopathies: Late-onset
Muscular dystrophies (MDDG)
Distal myopathies
Ehlers-Danlos: Recessive
TNXB; 6p21
FKBP14; 7p14

FSH dystrophy: Dominant
FSHD1: D4Z4 deletion; 4q35
FSHD2: SMCHD1; 18p11 & 4q35
Glycogenoses
Glycosylation
Inclusion Body (IBM)
HMERF: TTN; 2q31; Dominant
IBM1: Desmin; 2q35; Dominant
IBM2: GNE; 9p12; Recessive
IBM3: MYH2; 17p13; Dominant
IBM4: 7q22; Dominant
LGMD 1D: DNAJB6; 7q36; Dominant
IBM + Paget
Lipid
Mitochondrial
Myasthenia gravis, Familial
Myotonic dystrophy
Ophthalmoplegia: MYH2; 17p13; Recessive
Other dystrophies
Respiratory failure
Scapuloperoneal syndromes
Skeletal + Myopathy: Dominant
Bone fragility: MTAP; 9p21
Paget (VCP; HNRNPA2B1; HNRNPA1)
Dysplasia
Diaphyseal: TGFB1; 19q13
Epiphyseal (COL9A3; COL9A2; COMP)
Strongman: DCST2; 1q22; Dominant

LGMD: General features

Inheritance
Myopathy: General features
Presenting features
Prevalence
Proteins: Subcellular location
Sarcoglycans
Weakness

From Bramwell:
Atlas of Clinical Medicine

MD: Toe walking

Definitions
- Dystrophy (Classic)
  - Tissue involved: Myopathy
  - Course: Progressive
  - Etiology: Genetic
- LGMD ¹¹²
  - Tissue involved: Muscle
  - Etiology: Genetic
  - Weakness: Predominantly proximal
  - Serum CK: High
  - Muscle histology: "Dystrophic"
  - Course: Progressive
  - Atypical LGMD
    - 1A (Myotilin): Distal weakness
    - 1B (LMNA): Cardiac arrhythmias
    - 1C (CAV3): Mainly rippling muscles & Myalgias
    - 1E & 2R (Desmin): Distal weakness; Cardiomyopathy
    - 2V: Glycogen storage disease
  - LGMD: Previous classification
    - LGMD1: Dominant
      - 1A: Myotilin; 5q31; Dysarthria
      - 1B: Lamin A/C; 1q21; + Cardiac
      - 1C: Caveolin-3; 3p25; Child onset
      - 1D: DNAJB6; 7q36
      - 1E: Desmin; 2q35
      - 1F: TNPO3; 7q32
      - 1G: HNRPDL; 4q21
      - 1H: ? 3p23
      - 1I: Calpain-3; 15q15
    - LGMD2: Recessive
Myopathies: General features
Inheritance
- LGMDD (LGMD1): Dominant
- LGMDR (LGMD2): Recessive
- X-linked
- Other
Weakness
- Typical
  - Slowly progressive
  - Symmetric
  - Proximal
- Severe: Duchenne; Sarcoglycanopathy (LGMD 2C, 2D, 2E, 2F); LGMD 2A (Some patients)
- Mild: Becker; LGMD 1G, 2A, 2B, 2G
- Distinctive, selective patterns
  - Extraocular
  - Arm
  - Quadriceps
  - Paraspinous: 2B
  - Distal: LGMD 1C; 2B
  - Asymmetric
  - Scapular
Other distinctive features: Dystrophies may also present with
- Myoglobinuria
- Pain
- Myotonia
- Systemic signs
- Contractures
- CNS
- Muscle hypertrophy
- Cardiomyopathy
- High serum CK: Especially DMD, Sarcoglycanopthies, LGMD 2B
- Rippling muscles: LGMD 1C
- Vacuoles
Carriers: Have increased Serum CK in < 5% of cases

Subcellular localization of myopathy-related proteins
- Nucleus
- Cytosol
- Golgi
  - FKRP: LGMD2I; Congenital Muscular Dystrophy (MDC1C)
  - GOSR2: Congenital MD; Ataxia + Epilepsy
  - TRAPPC11: Myopathy with Movement Disorder & Intellectual Disability
  - GOLGA2: CNS + Muscle
- Myofibrillar
- Z-disk related
  - MYOT: LGMD1A
  - DNAJB6: LGMD1D
  - DES: LGMD1E; LGMD2R
  - TCAP: LGMD2G
  - TTN: LGMD2J
  - PLRC1: LGMD2Q
- Cytoskeleton
- Contraction-related cytoskeleton
  - α-Actin (ACTA1): Rod myopathy
  - α-Tropomyosin 3 (TPM3): Rod myopathy (NEM1)
  - Troponin T1: Rod myopathy
  - Myosin: Acute quadriplegic myopathies; Hypertrophic cardiomyopathies; Hearing loss
- Sarcolemma
- Sarcoplasmic reticulum
  - Ryanodine receptor: Central core
  - Calcium ATPase (ATP2A1): Brody's syndrome
  - Calcium Channel, α1 subunit (Dihydropyridine Receptor) (CACNA1S)
    - Hypokalemic periodic paralysis
    - Malignant hyperthermia
- Extracellular matrix
- α-dystroglycan ³³
  - Disorders
  - Abnormalities may involve DAG1 mutations or abnormal glycosylation due to other mutations
Prevalence
- LGMD general: 1 to 6 per 100,000
- Recessive muscular dystrophies
  - LGMD 2A: Common on Réunion Island, Guipuzcoa, Northern Indiana, Russia
  - LGMD 2C: Most prevalent in Tunisia
  - LGMD 2D: Most prevalent in US, Europe & Brazil
  - Brazil: Relatively high frequencies of LGMD 2E (8%); 2F (6%); 2G
  - Manitoba Hutterites of Canada: LGD 2H
  - Denmark & England: LGD 2I
  - Finland: LGD 2J
  - French-Canadian: LGD 2L
Dystrophin-associated glycoprotein (DAG; Sarcoglycan) mutations: Typical features
- Mutations in one DAG often also result in reduced amounts of the others in muscle
- Severe weakness
- Very high serum CK
- Complexes of DAGs are different in extrasynaptic muscle than at neuromuscular junctions
Also see: Metabolic disorders

LGMDD (LGMD 1): Dominant inheritance

LGMD D1

⁸²
● DNAJ/HSP40 Homolog, subfamily B, Member 6 (DNAJB6)

; Chromosome 7q36.3; Dominant

Nosology: Confused terminology
- LGMD 1D: HUGO
- LGMD 1E: OMIM & Some authors ³⁵
Epidemiology
- DNAJB6 mutations in 12 families
- US, Japan & Europe
Genetics
- Mutations
  - Location: G/F domain (Exon 5)
  - Types
    - Missense
    - Splice site: Removes glycine/phenylalanine-rich region (G/F domain)
    - Inframe deletion: Asp98del
  - Hotspot: Phe93
  - Clinical correlations ⁹⁹
    - Severe disease: c.346+5G>A (ΔG/F); Phe91
    - Intermediate disease: Phe100, Pro96, Phe89
    - Milder disease: Phe93
    - Limb girdle phenotype: Proximal G/F domain mutations; Phe89, Phe91, Phe93
    - Distal onset: Distal G/F mutations; Pro96, Phe100
    - Bulbar: Phe100
- Allelic with
  - Distal Dystrophy with Rimmed Vacuoles
  - Cardiomyopathy susceptibility
DNAJB6 protein
- Cell location
  - A isoform: Nucleus
  - B isoform: Cytoplasm; M-band > Z-band
- Expression
  - Muscle: Z-disk
  - CNS
    - High levels
    - Inhibits polyglutamine (PolyQ) aggregation
    - Component of Lewy bodies
  - Other tissues
- Chaperone-related
  - Protects client proteins from irreversible aggregation
  - Interacts with BAG3; HSP70
  - HSP40/DNAJ co-chaperone family: Features
    - Regulate molecular chaperone activity by stimulating ATPase activity
    - Associate with: HSP70 ATPases (e.g., HSPA4 )
    - Stimulate protein folding & remodeling reactions in endoplasmic reticulum
  - Other chaperone-related protein disorders
- Ligands: MLF1 ; HSPA8 ; KRT18
- Mutation effects: Reduced capacity to prevent protein aggregation
- HSP40/DNAJ family: Other DNAJ disorders
  - DNAJB2: Motor neuropathy; CMT 2T
  - DNAJB5: Distal atrophy
  - DNAJC3: Diabetes Mellitus & Multisystem Neurodegeneration
  - DNAJC6 : PARK19
  - DNAJC12 : Hyperphenylalaninemia, Dystonia & Intellectual Disability
  - DNAJC19: Dilated Cardiomyopathy with Ataxia
  - DNAJC21 : Bone marrow failure
Clinical
- Onset age
  - Mean: 38 years
  - Range: 8 to 50 years
- Weakness
  - Distribution: Variable
    - Proximal > Distal or Distal > Proximal
    - Legs > Arms
    - Hamstring > Quadriceps: Some patients
    - Respiratory: Some childhood onset patients
  - Progression: Slow; Wheelchair after 20 to 30 years
- Dysphagia (20%)
- Muscle size: Atrophy in some patients
- Cramps: Some patients
- Systemic features: None
Laboratory
- Serum CK: Normal to 5x elevated
- EMG: Myopathic; Some with irritability
- MRI
- Muscle pathology
  - Myopathic
  - Rimmed vacuoles: Associated with autophagy markers TDP-43, LC3, SQSTM1
  - Eosinophilic cytoplasmic bodies
  - Aggregates: Contain SMI-31, TDP-43, αB-crystallin, Myotilin, Desmin, DNAJB6
  - Small fibers express neonatal & fetal myosin

LGMD D2

³⁵
● Transportin 3 (TNPO3)

; Chromosome 7q32.1; Dominant

Nosology: LGMD 1F
Epidemiology 1 Spanish family
Genetics
- Mutation: c.2771del
- Penetrance: 85%
- IRF5-TNPO3 region: rs10488631 is risk locus for Systemic Lupus Erythematosus
TNPO3 protein
- Location: Nuclear
- Transport into nucleus
  - Serine/arginine rich proteins
  - HIV
Clinical
- Weakness
  - Onset
    - Age
      - Mean: 16 years
      - Range: 1 to 58 years
    - Proximal leg
  - Distribution
    - Proximal: Early in disease course;
    - Symmetric
    - Legs > Arms
    - Scapular winging: Some patients
    - Distal
      - Late in course
      - Muscles: Extensor digitorum, Tibialis anterior, Toe extensors
    - Face: Normal in most
    - Early-onset or More severe patients: Weakness
      - Face
      - Proximal & Distal
      - Respiratory: Younger onset patients; FVC 40%
      - Progression more rapid
    - Progression: Linear rate
      - Slow: Adult onset patients
      - More rapid: Juvenile onset patients
      - Wheelchair in 2nd or 3rd decade in younger onset patients
- Muscle hypertrophy: Absent
- Skeletal
  - Contractures: Occasional late; Ankles
  - Spinal deformity: Some younger onset patients
Laboratory
- Muscle pathology
  - Fiber size: Varied
  - Necrosis: Occasional
  - Connective tissue, Endomysial: Increased
  - Desmin: Mildly increased expression in some fibers
  - Nuclei: Abnormal morphology, Internal
  - Rimmed vacuoles (60%)
  - Ultrastructure: Autophagic vacuoles
- Muscle MRI: Most involved muscles
  - Scapular girdle: Teres major (80%) > Pectoral (64%), Iinfraspinatus & Serratus anterior (55%), Deltoids (46%)
  - Lumbar: Paraspinal (90%) > Abdominal oblique (55%) Rectus abdominus (55%)
  - Thigh: Sartorius (100%) > Vastus lateralis, intermedius & medialis (73%), Biceps femoris, Semitendinosus (55%)
  - Lower leg: Peroneal (91%) & Gastrocnemius (91%) > Soleus (73%), Tibialis anterior (70%)
- EMG: Myopathic or Neurogenic
- Serum CK
  - Mean: 589
  - Normal: 40%
  - Range: 47 to 2,920
- Cardiac: Normal EKG & Echocardiogram

LGMD D3

● Heterogeneous nuclear ribonucleoprotein D-like protein (HNRNPDL; HNRPDL)

; Chromosome 4q21.22; Dominant

Nosology: LGMD 1G
Epidemiology: Brazilian-Caucasian & Uruguayan families; 18 patients
Genetics ⁹²
- Mutations: Missense in same base pair; G>A (p.D378N), G>C (p.D378H)
HNRPDL protein
- HNRPDs: Participate in splicing of specific exons in premRNA of transcripts
- Location
  - Normal muscle: Nuclei
  - Disease: Irregular nuclei; Also present around nuclei
- May interact with: Transportin-1 (TNPO1) in RNA-processing events
- Ribonuclear proteins & Disorders
Clinical
- Homogeneous phenotype
- Onset
  - Age
    - Range: 15 to 53 years
    - Mean 37 years
    - Some mutation carriers asymptomatic > age 63
  - Weakness: Legs or Arms; Proximal
  - Cramps: Legs
  - Cataracts (50%)
- Weakness
  - Proximal > Distal
  - Legs 100%; Arms 90%
  - Finger & Toe flexion: Limited
- Muscle atrophy
- Contractures: Limited flexion of fingers & toes
- Progression
  - Slow
  - 50% walking at 10 years after onset
- Eye: Cataracts
Laboratory
- EKG: Normal
- Hand x-rays: Normal
- Serum CK: Usually high (Up to 9x normal); Normal in 20%
- Muscle biopsy
  - Fiber size variation
  - Perimysial fibrosis (Discrete)
  - Necrotic fibers
  - Vacuoles
    - Rimmed
    - Stain with dystrophin & sarcoglycans
  - Type 2 fiber predominance
  - Denervation-like
    - Small atrophic angulated fibers
    - Fiber type groups: Scattered
  - Milder patients: May be normal

Myofibrillar myopathy 3 (MFM3)
● Myotilin (Titin immunoglobulin domain protein (TTID); MYOT)

¹⁹; Chromosome 5q31.2; Dominant or Sporadic

Nosology: LGMD 1A
Epidemiology
- > 15 families described
- Female = Male
- 10% of myofibrillar myopathies
Genetics
- Mutations
  - Missense
    - Most common: Ser60Cys
    - Lys36Glu; Ser55Phe; Thr57Ile; Ser60Ile; Gln74Lys; Ser95Ile; Ala115Thr
  - Most common in: Exon 2; Serine rich region of myotilin
  - Other exon mutations: Arg6His (Exon 1); Arg405Lys (Exon 9)
- ~50% of families have no family history: Not related to specific mutation
- Allelic disorders
- Also see: Myofibrillar myopathies
- External link
  - Gene data base: Caveolin-3; Sequence variants
Protein: Myotilin (Titin immunoglobulin domain protein; TTID)
- Structure: Contains 2 Ig-like domains in C-terminus homologous to titin
- Location
  - Sarcomere: In I-bands (Z-line); Bound to α-actinin
  - Sarcolemmal membrane
- Interacts with: α-Actinin; Actin; Filaments (γ-Filamin)
Clinical features ⁴⁰
- Onset
  - Age: Variable
    - Young adults in Virginia family (Thr57Ile): Mean age 27 years
    - Other patients: 42 to 77 years
  - Weakness
    - Legs
    - Distal or Proximal
  - Myalgias & Stiffness: Some patients
- Weakness
  - Legs & Arms
  - Distal
    - With disease progression in most
    - Many patients with early foot drop
  - Arms: Wrist & finger extensors + Deltoids most common
  - Neck extensors: Some patients
  - Face: 17%
  - Symmetric: Most patients
  - Respiratory failure: Some patients; At onset in 1 patient
- Speech: Dysarthria, nasal (30%); ? Related to palatal weakness
- Myalgias: 25%
- Tendon reflexes: Reduced at knees & ankles (100%); Some with diffuse loss
- Joint Contractures: Ankles (30%)
- Cardiomyopathy: 50%; Onset in 6th or 7th decade
- Neuropathy: Occasional patient
  - Sensory loss: Distal
  - Axonal loss
  - Demyelinating features: One patient
- Progression
  - Slow
  - Late loss of ambulation (10 years after onset)
Laboratory
- Serum CK: Normal to 15-fold elevated; Commonly 2x high
- EMG
  - Myopathic
  - Fibrillations: Some patients
  - Myotonia: Some patients
- CT: Early posterior leg involvement
Muscle pathology
- Myopathic
- Rimmed vacuoles: Numerous; Autophagic; No amyloid
- Inclusions
  - Hyaline: Some congophilic; Composed of compacted, fragmented filaments
  - Rod-like inclusions: Z-band streaming
  - May be PAS positive
- Inflammation: 1 patient; Mild
- Immunocytochemistry
  - Myotilin
    - Normal levels
    - Abnormal muscle fibers often have patches of increased immunostaining
    - Co-localizes with ubiquitin & clusterin
  - Normal DAG staining
  - Increased staining: Other molecules in abnormal muscle fibers
    - Common to myofibrillar myopathies: Dystrophin; NCAM; Desmin; Plectin
    - More prominent than in other myofibrillar myopathies: Gelsolin; Ubiquitin
  - Reduced staining
    - Laminin γ1
- Denervation: Small esterase positive muscle fibers
Variant syndrome: Spheroid body myopathy ⁵²
● Myotilin ; Chromosome 5q31; Dominant
- Epidemiology: Indiana & Oregon families
- Genetics
  - Mutations: Missense; S39F in myotilin gene exon 2
- Clinical: Variable within family
  - Onset: Teens to 80's; Mean 4th decade
  - Weakness
    - Proximal ± Distal
    - Legs
    - Symmetric
    - Dysarthria
    - Respiratory
  - Tendon reflex: Absent ankle
  - Prognosis
    - Usual: Benign; Little disability
    - Some patients: Rapid progression to wheelchair or respiratory failure
- CK: Normal
- Pathology
  - Variation in fiber size: Moderate
  - Inclusions
    - Aggregates of Gomori Trichrome + & Eosinophilic material
    - Contain Desmin & Ubiquitin
    - Type I > Type II fibers
    - Often subsarcolemmal; ± Associated with acid phosphatase staining
    - PAS -
Variant syndrome: Myofibrillar myopathy, Recessive ⁹⁵
● Myotilin ; Chromosome 5q31; Recessive
- Epidemiology: 1 German family, 2 patients
- MYOT mutation: Arg6Gly, Homozygous
- Clinical
  - Severe phenotype: Intrafamilial variability
  - Onset age: 3rd or 4th decade
  - Weakness: Proximal; Legs > Arms; Progressive
- Laboratory
  - Serum CK: 1143
  - Muscle pathology: Myofibrillar myopathy
    - Fiber size: Varied
    - Subsarcolemmal & intracellular masses
    - Protein aggregates: Desmin; αB-crystalline; Myotilin
    - Ultrastructure: Myofibrillar damage
  - EMG: Myopathic
  - Muscle MRI: Vastus involvement
  - Cardiac: Mild EKG changes
Variant syndrome: Homozygous Dominant disease
- Genetics: Ser60Phe mutation
- Clinical
  - Onset age: Adult
  - More severe disease
  - Proximal & Distal weakness

Myopathy, Dominant

¹⁷
● Lamin A/C

; Chromosome 1q21.2; Dominant

Nosology: LGMD 1B
Genetics
- Lamin A/C gene mutation types
  - Missense & Deletion of codon in rod domain
  - Splice donor site: Protein lacking half of the globular tail domain
- Lamin A/C gene mutations: Other clinical syndomes
Lamin A/C protein
Clinical
- Onset: < 20 years
- Weakness
  - Common: Symmetric; Proximal; Lower limb
  - Variant: Quadriceps with Arg377His mutation
- Progression: Slow; Upper limbs involved by 3rd or 4th decade
- No contractures
- Associated systemic feature: Cardiomyopathy (62%)
  - A-V conduction block
  - Occasional dilated cardiomyopathy: Onset before weakness with Arg377His mutation
Laboratory features
- Serum CK: Normal to mildly elevated
- Muscle
  - Myopathic changes, Mild
  - Aggregates: Desmin, Myotilin, α-B-Crystallin, Dystrophin
- Lamin A subcellular localization
  - Normal: Nucleus; Co-localizes with Emerin
  - Mutated: May aggregate in nucleus & be present in cytoplasm
Also see: Dominant myopathy with cardiomyopathy

LGMD 1C

²⁷
● Caveolin-3

; Chromosome 3p25.3; Dominant, Also Recessive

Caveolin protein LGMD 1C Allelic disorders Clinical Genetics Laboratory Mouse models
	Caveolin-3: Located on muscle fiber sarcolemma

Genetics
- Caveolin-3 gene mutations
  - General: Most commonly located in scaffolding domain of protein
  - Specific mutations
    - Arg26Gln
      - Caveolin levels reduced 60% to 80%
      - Disease associations
        
        Idiopathic hyperCKemia
        
        Rippling muscle disease
        
        Distal myopathy
    - Asp27Glu
      - Rippling muscle disease ± Weakness (Distal or Proximal)
      - Variable clinical features in family
    - Pro28Thr
      - Onset 35 years
      - Rippling muscle disease
      - Fatigue: Exercise induced muscle pain, Cramps
      - Serum CK: 1100
    - Ala45Thr
      - N-terminal domain
      - Disease associations: LGMD1C; Rippling muscle disease
      - Caveolin levels reduced > 90%
    - Ala45Val: Rippling muscle disease
    - Ala46Thr: Rippling muscle disease; Distal myopathy
    - Ala46Val: Cardiomyopathy with Rippling muscles
    - Ser52Gly
      - Domain with role in homo-oligomerization
      - Rippling muscle disease
    - Gly55Ser
      - Caveolin scaffolding domain
      - Inheritance: Recessive
      - Caveolin levels: Normal
    - Val57Met: HyperCKemia
    - T63S: Cardiomyopathy
    - Cys71Trp: ? Disease association
      - Caveolin scaffolding domain
      - Caveolin levels: Normal
    - Homozygous: L86P or A92T
      - Rippling muscle disease: Severe, Recessive
    - Pro104 Leu
      - Missense mutation in membrane-spanning region
      - Disease associations: LGMD1C; Rippling muscle disease
      - Caveolin levels reduced > 90%
    - Arg125His: ? Disease association
      - C-terminal domain
      - Caveolin levels normal
    - 186Del9
      - Microdeletion in the scaffolding domain
      - Caveolin levels reduced > 90%
    - Splicing: IVS1+2T>C ⁶⁴
      - Homozygous
      - Intronic
      - Recessive inheritance
- Caveolin-3: Allelic disorders
  - LGMD 1C
  - Rippling muscle disease: Dominant or Recessive
  - Increased CK with normal strength
  - Distal myopathy
  - Cardiomyopathy, familial hypertrophic
  - Long QT syndrome 9
- External link: Leiden database
Caveolin proteins
- Caveolins: General
  - Integral transmembrane proteins
  - Principal protein components of caveolae
  - Caveolin-1 & Caveolin-3 generate caveola-like vesicles
  - Most of the functional domains in caveolins located in last exon
  - Functions
    - Signaling
      - Able to bind multiple components of a signaling pathway
      - Implicated in signal transduction: By receptor tyrosine kinases (RTKs) & G-proteins
      - Mechanism: Scafolding proteins; Organize & Concentrate molecules
        
        Lipids: Cholesterol; Glycosphingpolipids
        
        Lipid-modified signaling molecules in caveolar membrane
        
        Src-like kinases, H-ras, eNOS, G proteins
    - Vesicular trafficking events
    - ? Tumor supressor (Caveolin-1)
- Caveolae
  - Structural
    - 50 to 100 nm invaginations found in most cell membranes
    - Appendages or subcompartments of plasma membranes
  - Functional
    - ? Provide a scaffold
    - Place members of a signal-transduction pathway in close proximity to each other
  - Disease: Duchenne MD muscle has increased numbers of caveolae
- Caveolin-3 protein
  - Tissue location: Muscle specific, Striated & Smooth
  - Cell localization
    - Sarcolemma (Adult)
    - T-tubules (Development & Adult): Concentrated in subsarcolemmal regions
  - Forms homo-oligomer: 14 to 16 subunits
  - Caveolin-3 interacts with
    - G-protein α subunits
    - Signaling molecules: Gl2α; Gβγ; c-Src; Src-like kinases
    - Dystrophin & Associated glycoproteins
      - Interaction not as strong as integral members of the DAG complex
      - Direct interaction with β-dystroglycan: Via WW-like domain
    - Dysferlin
    - PFK-M
      - Prominent caveolin-3 binding protein
      - ? Regulation of glycolysis by caveolin-3
    - nNOS (muscle-specific): Interaction inhibits nNOS enzyme activity
      - Cytokine-stimulated NOS activity: Increased in myotubes transfected with mutant CAV3
      - Transgenic CAV3 mutant mice (P104L): Increased nNOS activity in skeletal muscle
      - LGMD1C: Severe reduction of nNOS expression
    - Colocalizes with Na_v1.5 (SCN5A) in myocardium
  - Muscle functions
    - Required for myoblast fusion/myotube formation
    - Regulates myostatin signaling: Suppresses activation of type I myostatin receptor
    - Sarcolemma integrity
    - Electrical transmission of contractile impulse
    - Energy metabolism
- Caveolin gene mutations & Other Disorders: Effects on caveolin-3 protein
  - LGMD 1C
    - Reduced Caveolin-3 levels in muscle: Membrane caveolin-3 especially reduced (~95%)
    - Mutations cause formation of unstable high molecular mass aggregates
    - Aggregates composed of normal & mutated caveolin-3: Dominant negative effect
    - Aggregates of normal & mutated caveolin-3
      - Cell location: Retained in Golgi; Not targeted to plasma membrane
      - Effect of aggregation on caveolin-3 protein: Misfolding; Degradation
      - Metabolism: Undergo ubiquitination & proteasomal degradation
      - Caveolin-3 Half-life: Shortened by 7 fold
      - ? Treatments rescue wild type caveolin-3
        
        Inhibition of proteasomal degradation of caveolin-3 aggregates
        
        Inhibition of caveolin-3 misfolding
    - Altered interactions of scaffolding region with muscle regulatory proteins
  - Duchenne MD: Caveolin-3 is upregulated
  - Denervation: Caveolin-3 aggregates are present inside targets
LGMD 1C: Clinical features
- Onset
  - Age: 4 to 71 years
  - Weakness
  - Difficulty walking
- Weakness
  - Usual
    - Severity: Moderate
    - Pattern: Proximal
  - Distal
    - 2 families described
    - Also in recessive patients
  - Progression
    - Mild: Adults with Gower's maneuver
    - Variable among families
- Calf hypertrophy
- Exercise intolerance ± Weakness
  - Cramps: After exercise
  - Rhabdomyolysis
- Variable clinical manifestations may occur in single family
Caveolin-3 mutations: Variant syndromes
- Recessive muscular dystrophy syndromes ⁶⁴
  - Mutations: Gly55Ser; Splice site (IVS1C2TOC)
  - Weakness
    - Proximal & Distal; Foot drop
    - Legs & Arms
  - Contractures: Ankles
  - Calf hypertrophy
  - MRI
    - Asymmetric
    - Muscles: Hip abductors & adductors, Rectus femoris, Hamstring, Tibialis anterior
  - Muscle biopsy
    - Chronic myopathy
    - Caveolin-3 absent: No 21 kD band on Western blot
- Rippling muscle disease syndromes
- Distal myopathy (MPDT)
  - Nosology: Tateyama myopathy
  - Epidemiology: 3 families
  - Genetics
    - Inheritance: Dominant
    - Mutations: Arg26Gln; N33K mutations
  - Clinical
    - Weakness
      - Onset age: 2nd to 5th decade
      - Isolated Hand & Foot muscles
      - Neck flexors: Mild
    - Muscle size
      - Calf hypertrophy
      - Distal wasting
    - Percussion induced muscle contractions: Distal hands
    - Some patients
      - Rippling
      - Myalgias
      - Pes cavus
  - Laboratory
    - Serum CK: High
    - EMG: Myopathic
    - Muscle
      - Internal nuclei
      - Type I predominance
      - Caveolin-3 nearly absent
      - Dysferlin: May be reduced or normal
- Hyper-CKemia ⁶³
  - Mutations: Missense; Gly56Ser, Thr78Met
  - Frequency: 7% of Idiopathic Hyper-CKemia
  - Caveolin-3 staining of muscle: Normal
- Cardiomyopathy: Varied types
  - Hypertrophic
  - Dilated
  - Long QT syndrome ⁶⁵
    - Mutations: Missense; T78M, A85T, F97C, S141R
    - Effect of mutations: 2- to 3-fold increase in late sodium current
    - Onset age: 8 to 40 years
    - Symptoms: Nonexertional syncope; Cardiac arrest; Shortness of breath
LGMD 1C: Laboratory features
- Serum CK: Increased 3 to 40-fold
- Pathology ⁶⁶
  - Myopathic changes: Often mild
    - More severe with early disease onset
    - Muscle fiber size: Varied
    - Necrosis & Regeneration: Some patients
    - Endomysial connective tissue increased: Some patients
  - Caveolin-3
    - LGMD1C
      - Reduced on muscle fiber sarcolemma & by Western blot
      - May be normal or high on small, regenerating muscle fibers
    - Reduced on sarcolemma in other hereditary disorders
      - VCP myopathy (IBMPFTD)
      - Cavin-1
  - Dysferlin
    - Reduced on muscle fiber sarcolemma
    - Normal by Western blot
  - Ultrastructure
    - Reduction in caveolae
    - Loss of myofibrils
Caveolin disorders: Mouse models
- Overexpression of wild type caveolin-3
  - Myopathy
  - Reduced dystrophin
- Overexpression of Pro104Leu mutant caveolin-3
  - Down regulation of wild type caveolin-3
  - Myopathy: Severe
- Caveolin-null
  - T-tubule abnormalities
    - Mislocalized dihydropyridine receptor-1α & ryanodine receptor
    - Iregular orientation of T-tubules
  - Loss of caveolae at sarcolemmal membrane
  - Muscle fiber degeneration: Especially in soleus & diaphragm
  - No effect on dystrophin complex
Links: Leiden

Familial Dilated Cardiomyopathy with Conduction Defect & Muscular Dystrophy

⁸¹
● Desmin; Chromosome 2q35; Dominant

Nosology: Confused terminology
- LGMD 1E: HUGO
- LGMD 1D: OMIM & Some authors ³⁵
- Myofibrillar myopathy 1 (MFM1)
Epidemiology: 1 Large family; French-Canadian descent
Genetics
- Desmin mutation: Intron splice donor site mutation (IVS3+3A>G)
- Earlier incorrect chromosome localization at 6q23
- Allelic disorders
Desmin protein
Clinical
- Weakness
  - Onset: 2nd decade & later
  - Distribution: Proximal; Face normal
  - Calf hypertrophy: Occasional
  - Exertional dyspnea
  - Progression: Slow; All patients remain ambulatory
- Cardiac
  - Arrhythmia: Earliest feature of cardiac disease; Onset 20 to 25 years
  - Congestive heart failure: 4 chamber enlargement; Onset 3rd to 5th decade
  - Sudden death without prior cardiac symptoms
Laboratory
- Muscle pathology
  - Variable fiber size
  - Increased endomysial connective tissue
  - Eosinophilic inclusions: Some reducing bodies
- Serum CK
  - Usually increased 2x to 4x control
  - More likely high in males than females

Myopathy, Dominant

⁷⁷
● ? Chromosome 3p25.1�p23; Dominant

Nosology: LGMD 1H
Epidemiology: Southern Italian family
Genetics: Incomplete penetrance
Clinical
- Onset
  - Age: 16 to 50 years
  - Weakness: Arms & Legs
- Phenotype: Variable onset age & severity
- Weakness
  - Proximal
  - Legs & Arms
  - More severe with younger onset
- Muscle hypertrophy
  - Calves
  - Younger patients with no weakness
- Muscle atrophy: Proximal
- Tendon reflexes: Reduced
- Progression: Slow
Laboratory
- EMG: Myopathic
- Serum CK: 98 to 2300
- Serum lactate: Normal
- Muscle biopsy
  - Fiber size variation
  - Endomysial fibrosis
  - Mitochondrial
    - SDH+ & COX- muscle fibers
    - mtDNA deletions: Multiple

LGMDR (LGMD2): Recessive Inheritance

LGMD R1

● Calpain-3 (CAPN3; p94 protein)

; Chromosome 15q15.1; Recessive or Dominant

Genetics
Calpain-3 protein
Clinical
Laboratory

From: C Angelini MD

Nosology: LGMD 2A
Epidemiology
- Most common recessive LGMD worldwide
  - Especially: Eastern Europe, Spain, Italian
  - Denmark: Less common than 2I & 2L
Genotype & Phenotype
- Mutations: > 500 identified ⁷
  - Mutation patterns
    - Private variant mutations in 70%
    - Recurrent mutations: Founder effect 1.5x more frequent than than recurrent
  - Single base pair: 60% to 70%
    - Missense: Most, ~80%
    - Stop codons: Few
    - Splicing defects: ~15%
  - Small insertions or deletions: 30% to 40%; Most cause frameshift & premature stop codon
  - 1 Large genomic deletion: 2° to unequal recombination between two intragenic Alu elements
  - Overall ~45% of mutations are truncating
  - Location: Present through most of gene
    - Excess of mutations: Exon 21
    - Excess of point mutations: Exons 5, 11 (11 amino acid span with multiple CpG sites) & 21
    - Excess of deletions/insertions: Exons 15, 17, & 22
    - R490Q mutation
      - Located in catalytic site
      - Protein is present by Western blot
      - LGMD phenotype: Variable severity of weakness
    - G222R mutation ⁵⁴
      - Mutations: Compound heterozygote for R110X & G222R
      - Loss of function: Size & Abundance normal
      - Early onset weakness
  - Disease foci
    - Multiple mutations in some foci: Réunion island
      - 60% have IVS6-1G®A
      - Amish & Basque populations
      - Digenic inheritance: ??
    - Single mutation
      - Guipuzcoa (Basque Country, Spain): Exon 22, 2362AG[rarr]TCATCT in 76%
      - US Northern Indiana Amish: R769Q in 100%
      - Russia, Eastern Mediterrananean & North Italy: 550delA; Mutation frequency 1/150
      - Venetian lagoon: R490Q
    - Other foci: Brazil, Turkey, Japan
  - Clinical correlations
    - Severe phenotype
      - Homozygous null mutations: Often but not always
      - NS1 domain mutations; S86F
    - Least severe phenotype: Homozygous missense mutations
    - S86F heterozygotes: Mildly high serum CK; Normal strength
- Allelic disorder: LGMD, Dominant
- Mutation Databases
  - HGMD
  - Leiden: Sequence variants
Calpain-3 (p94) protein
- Functions
  - General
    - Ca⁺⁺ activated non-lysosomal cysteine thiol-protease
    - Cleaves proteins into short polypeptides, not single amino acids
    - Activity may not be Ca⁺⁺ dependent
    - Use cysteine as active site residue
    - Limited proteolytic cleavage of substrate
  - Role in cytoskeletal remodeling
    - Assembly & remodelling of contractile proteins in sarcomere
    - Can bind & cleave titin
  - Control of Ca⁺⁺-efflux from the sarcoplasmic reticulum
  - Membrane repair
  - Muscle regeneration
  - Mutations: Reduced affinity of calpain-3 for titin
- Localization
  - Expressed prominantly in skeletal muscle: N₂-line region
  - Associates with
    - C-terminus of titin (connectin) in muscle
    - Filamin C
  - Subcellular: Nucleus ± Cytosol; Not membrane related
- Halflife
  - Short (< 10 minutes)
  - Rapid turnover related to insertion sequences (IS) not present in other calpains
- Disease mutations: Effects on calpain function vary, may be selectve for
  - Proteolytic activity vs fodrin substrate: Reduced
  - Autolysis capacity: Reduced
  - Titin binding: Reduced
LGD 2A: Clinical features ²¹

LGD 2A: Erb phenotype

From: C Angelini
- Onset
  - Early motor milestones: Most normal; Toe walking common
  - Range: 2 to 45 years; Median = 14 to 20 years; 71% between 6 to 18 years
  - Weakness: Proximal legs; Rectus abdominus
  - No clear sex differences; ? Females slightly younger than males
- Disease patterns: Various phenotypes
  - General pattern: Scapula, pelvic girdle & trunk weakness with normal face
  - Differential diagnosis: FSH; LGMD 2I
  - HyperCKemia, asymptomatic (14%): Male > Female 3:1
  - Limb girdle types (76%)
    - Early onset: < 12 year
      - Group with most homogeneous progression
      - Contractures more common
      - Null mutations common
    - Leyden-Mobius type
      - Onset 13 to 29 years
      - Weakness: Pelvic-femoral girdle
    - Late onset
      - Age: > 30 years
      - Weakness: Pelvic girdle
  - Erb dystrophy type (10%): Scapular-humeral phenotype
    - Onset age: 16 to 37 years
    - Weakness early in shoulder girdle
    - Male = Female
    - Calpain-3 in muscle: Often normal
  - Miyoshi muscular dystrophy phenotype
- Weakness
  - General
    - Symmetrical
    - Proximal + Milder Distal
    - Legs > Arms at onset: Most patients
    - May be asymmetric
    - Progressive
    - Severity
      - Heterogeneous: Mild to Early onset severe
      - Mild phenotype in majority
      - Male = Female
  - Trunk
    - Peri-Scapular
      - Latissimus dorsi; Serratus magnus
      - Scapular winging (83%): Symmetric
    - Rectus abdominus
    - Pelvic girdle
    - Gluteus maximus
  - Legs
    - Most severe: Adductors; Knee flexion
    - Ankle dorsiflexion: Some patients
  - Arms
    - Most severe: Shoulder adduction; Elbow flexion
    - Wrist extension: Some patients
  - Respiratory
    - Vital capacity: Declines over time; Rarely < 80%
    - No nocturnal hypoventilation
  - Quadriceps: May be selectively spared
  - Gait
    - Inability to walk on heels
    - Lumbar lordosis
    - Loss of walking: Mean late 2nd or 3rd decade
  - Normal: Face; Ocular & Bulbar
  - Some patients are asymptomatic with elevated serum CK levels
- Muscle size
  - Atrophy
    - Early in posterior compartments of limbs
      - Different from Quadriceps wasting in Sarcoglycanopathies
      - May be apparent on CT
    - Most affected: Gluteus maximus & Thigh adductors
    - Pelvic; Shoulder; Proximal limbs; Trunk; May be scapuloperoneal
  - Hypertrophy
    - Some patients: Especially in Brazil
    - Calf most common: Not prominent
- Contractures
  - Onset: May occur early in disease course
  - Calf: Toe walking may be presenting sign
  - Other: Elbow, Wrist & Finger flexion
  - Common late in disease progression: Rigid spine
  - May be severe & require surgery
  - Differential diagnosis: Emery-Dreifuss
- CNS
  - Normal, or
  - Mild mental retardation: Average IQ = 77
- Cardiac: No involvement
- Progression
  - Slow: Earlier onset more rapid
  - Loss of walking
    - 10 to 30 years after onset
    - 50% in 3rd decade
    - Most by age 40 years
  - Many patients can still stand, even when in wheelchair
- Syndrome variation
  - Intrafamilial
    - Similar onset age & severity in some families with null mutations
      - Onset at 15 years
    - Variation in others with
      - 2 Missense mutations or
      - Compound heterozygotes for missense & null mutation
      - Onset 2.5 to 45 years
  - Interfamilial: Prominent
LGD 2A: Lab features
- Serum CK: Normal to 80 times normal; 190 to 11,000
- MRI
  - Thigh: Varies with degree of function
    - Prominent in most patients: Posterior
    - Early involvement: Adductors; Semimembranosus
    - Restricted ambulation
      - Diffuse involvement: Posterolateral thigh & Vastus intermedius
      - Sparing: Vastus lateralis, Sartorius & Gracilis
  - Calf
    - Involvement: Soleus; Gastrocnemius, Medial head
    - Relative sparing: Gastrocnemius, Lateral head
- Muscle Biopsy
  - Myopathic
    - Muscle fibers
      - Necrosis & Regeneration
        
        Active myopathic changes
        Eosinophils in some associated cellularity
        Myopathic groups: May involve clusters or whole fascicles early in disease ³⁴
      - Size: Variable; Small rounded to Hypertrophic
      - Internal architecture
        
        Usually unremarkable
        
        Regenerating fibers: Coarse internal architecture
        
        Lobulation of Type I fibers: Later in disease course
        
        Nuclei: Internal; Apoptosis with altered IκBα/NF-κB pathway
        Groups of atrophic (type 2) muscle fibers
    - Endomysial fibrosis: Increased with longer disease course
  - Fiber types
    - Type 2 hypertrophy: Some patients
    - Type I predominance: With increasing weakness
    - Type 2C: Common
  - Inflammation
    - Some biopsies
    - May be perivascular or endomysial
  - Dystrophy-related proteins
    - Calpain-3: Western blot patterns
      - Loss of all calpain-3 bands (94 kDa, 60 kDa & 30 kDa)
        
        High specificity for LGMD2A: Frequency 23%
        
        May have null or missense mutations
      - Absence or reduction of 60 kDa bands: Highly specific (94%); Sensitive (64%)
      - Absence or reduction of 30 kDa bands: Specific (88%); Sensitive (58%)
      - Increased lower MW 60 kDa region bands: No mutations (92%); Suggests protein degradation artifact
      - Normal full-sized calpain-3 protein
        
        Occurs in 23% of patients with 2 calpain-3 mutations
        
        Often have loss of autocatalytic function
      - Abnormal Western blot with only 1 calpain-3 mutation: Similar phenotype to patients with 2 mutations found
      - Calpain-3 reduction may occur in other myopathies
        Dystrophin; LGMD 1C; LGMD 2B (Dysferlin); LGMD 2I (FKRP); LGMD 2J (Titin)
    - Dysferlin: Reduced or absent in some patients; Western blot normal
    - Sarcoglycans & Dystrophin: Normal
  - Ultrastructure: Patchy damage to myofibrillar Z, I & A bands
- Diagnosis ⁴¹
  - Genetics
    - Difficult due to many different mutations
    - More common in some regions of gene: 87% of mutant alleles exons 1, 4, 5, 8, 10, 11 & 21
    - Some common mutations: 61% have one of eight mutations
    - Directed mutation analysis: Geographic groups
    - Some patients with only 1 detected mutation have typical LGD 2A phenotype: May be dominant
  - Western blot
  - Calpain-3 enzyme activity: Reduced
Mouse model: Calpain-3 knockout ⁴²
- Misaligned A-bands
- Abnormal sarcomere formation
CAPN3 variant syndrome: LGMD, Dominant (LGMD D4) ¹⁰⁴
- Nosology: LGMD 1I
- Genetics
  - Inheritance: Dominant
  - Mutation: 21-bp, in-frame deletion (c.643_663del21)
- Clinical
  - Onset age
    - Mean 34 years: 16 years later than Recesive LGMD 2A
    - Range: 13 to 84 years
  - Pain (50%): Muscle; Back
  - Weakness
    - Severity: Milder than LGMD 2A
    - Pattern: Similar to LGMD 2A
      - Paraspinal: Lumbar
      - Leg: Proximal
      - Distal leg: Gastrocnemius, medial
      - Arms: Proximal
    - Course: Variable
      - Severe disability: Some patients
      - Asymptomatic: Some patients
  - Muscle wasting: Proximal arms
- Laboratory
  - Serum CK: High in 90%; Range 169 to 9,000
  - Muscle MRI: Fat replacement
    - Trunk: Paraspinal
    - Pelvis: Glutei
    - Thigh: Hamstring
    - Leg: Gastrocnemius, medial
  - Muscle pathology
    - Myopathic
      - Internal nuclei
      - Fiber size: Varied
      - Necrosis: Scattered
      - Endomysial connective tissue: Increased
    - Calpain-3 protein: Loss to< 15%

LGMD R2

● Dysferlin

; Chromosome 2p13.2; Recessive

Gene
Protein
Clinical
Laboratory
Pathology
Variant syndromes
Mouse models

From: C Angelini

Nosology: LGMD 2B
Gene
- 55 exons
- Allelic with
  - Miyoshi distal myopathy (MM)
  - Distal myopathy with anterior tibialis onset (DMAT)
  - Variant syndromes
- Locus near, but different from, Welander distal myopathy
Gene mutations ²⁵
- > 450 different mutations described
  - 18% of patients with dysferlin deficiency have only 1 (heterozygous) mutation identified on 1 allele
- Mutation types
  - Types: Missense (26% to 46%); Nonsense (18% to 26%); Deletions; Insertions; Intron; Splice site
  - Distributed over entire coding sequence + Introns: Most mutations private variants
  - Most introduce stop codons or premature truncations of the dysferlin protein
  - Splice site (in-frame) mutation (A3443-33G) ⁵³
    - May allow some residual dysferlin protein production
    - Clinical phenotype: Milder
- Mutation locations in gene: Widely dispersed over coding sequence
- Variations in phenotype not well explained by mutation type
- Geographic distribution
  - Mutations present at low frequency in many populations: Typically
    - 1% of recessive LGMD
    - 33% of distal myopathies
  - Common in Libyan Jews: 1624delG; Carrier frequency up to 10%
  - Japanese
    - G2997T (Trp999Cys); G3370T: Mild disease phenotype; Later onset
    - G3510A: More severe disease; Earlier onset; High CK
    - Other common mutations: 3746delG; 4870delT
    - 3373delG: Japanese Miyoshi
  - Sueca, Spain: Arg1905X ⁵⁰
- External links
  - Mutation Databases: Leiden; Sequence variants
  - Diagnostic tool: Jain Foundation
Protein: Dysferlin
- Tissues: Skeletal muscle > Heart; Ubiquitously expressed at low levels
- Size
  - 230 kDa + Multiple lower weight bands
  - 55 exons
- Subcellular localization
  - Plasma membrane: Present at periphery of muscle fibers
  - T-tubules
  - Cytoplasmic vesicles: Trans-Golgi network secretory vesicles
- Homology to
  - Nematode spermatogenesis factor (fer-1): Required for cell fusion
  - Myoferlin: Plasma membrane & Nuclear envelope
  - Otoferlin
- Domains
  - Transmembrane: Short, C-terminal, hydrophobic
  - C2: 7 domains; Hydrophilic; Bind calcium & cellular membranes
  - Most of dysferlin protein intracellular
  - Extracellular domain: Small
- Interactions: Binds to ⁶²
  - Caveolin-3
  - AHNAK
    - Interaction mediated by calpain-3
    - Levels reduced in dysferlinopathies
  - Annexins A1 & A2
  - S100 Calcium binding protein A10
  - Calpain 3 (CAPN3)
  - β-parvin
  - Dihydropyridine receptor (DHPR)
  - Mitsugumin 53 (MG53; TRIM72) : May play role in membrane repair
  - Other: Ca⁺⁺; Lipids
- Functions
  - Membrane fusion or repair
  - Ca⁺⁺-mediated muscle membrane
    - Homeostasis processes
    - Signal transduction events
  - Myogenesis
  - Angiogenesis
  - Microtubule dynamics
- Dysferlin turnover & levels
  - Half-life in membrane: ~ 3 hours
  - Upregulation: LARGE (myd) mouse
- Dysferlin: LGMD 2B patients
  - Immunohistochemistry (IHC)
    - Sarcolemma: Absent or Reduced
    - Cytoplasm: Reduced or Increased
  - Western blot
    - Absence has more specificity for LGMD 2B than IHC changes
    - Dysferlin may be normal or increased
      - Some mutations produce cytoplasmic aggregates of normal sized dysferlin protein
Clinical: Milder LGMD phenotype ⁸⁵

LGMD 2B
No calf hypertrophy
- Onset
  - Age
    - Mean 19 to 27 years
    - Range
      - General: 10 to 39 years
      - Congenital & 8th decade onsets reported
    - Heterogeneity in single family may occur
  - Leg weakness
    - Proximal
    - May be associated with period of exercise
- Weakness
  - Mild
  - Asymmetry: Common
  - Legs
    - Distal: Posterior muscles
      - Especially gastrocnemius
      - Early inability to walk on toes
      - Differential diagnosis: Distal myopathy with anterior leg sparing
    - Proximal
      - Anterior & Posterior muscle groups
      - Especially adductors, also psoas
    - Lower limbs involved 9 years before upper limbs
  - Arms
    - Especially biceps
    - Deltoid: Often spared
  - Trunk: Glutei, Erector spinae, Shoulder girdle involved
  - Face: Generally normal
  - Loss of ambulation: > 30 years
  - Respiratory
    - More with longer disease duration
    - Overall: 50% have VC < 80%
  - Wide inter- and intrafamilial variation
  - Progression: Slow; Most walk until > 33 years, some into 6th decade
- Calf size
  - Hypertrophy: Some patients
    - Deltoid hypertrophy with biceps atrophy
    - Posterior leg (Calf): May be early in disease course
  - Occasional distal onset patients
    - Subacute, painful enlarged calves early in course ⁶⁰
- Cramps & muscle discomfort: Some patients
- No cardiomyopathy: Clinically preserved; EF generally > 50%
- Same mutations may also produce Miyoshi distal myopathy
  - ? Modifier genes determine phenotype
Laboratory features
- CK
  - Typical
    - Very high
    - Range: 10x to 72x normal; Up to 27,000
    - Lowest: Normal
  - Presymptomatic: 343 to 3,000
  - ? Age-dependent increase
- EMG: Myopathic
  - Motor units: Small amplitude; Short duration
  - No spontaneous activity
- Imaging
  - Early involvement on MRI or CT
    - Posterior leg: Gastrocnemius atrophy, especially medial heads; soleus
    - Thigh: Hamstrings
    - Erector spinae
  - Late or minimal involvement: Gracilis; Sartorius; Glutei
- Muscle
  
  Dysferlin staining
  in normal muscle
  - Pathology: Dystrophic Muscle
    - Necrosis & degeneration of muscle fibers
    - Endomysial connective tissue: Increased in more involved muscles
    - Muscle fibers: Size variation, may appear bimodal; Splitting
    - No vacuoles
    - Inflammation: Some mutations ²²
      - Perimysial & perivascular cell infiltrates: Some muscles
      - T-lymphocytes
      - No MHC class I antigen on muscle fibers
    - Complement: Membrane attack complex (but not C3) on muscle fiber surface
    - Amyloid
      - Present in muscle in some patients
        
        Mutation locations: N-terminal or other regions
      - Location: Muscle fiber surface; Endomysial connective tissue; Perivascular
      - Amyloid may contain dysferlin
    - Ultrastructure
      - Sarcolemmal defects
      - Replacement of membrane by layers of small vesicles ²³
  - Dysferlin tissue staining ³⁰
    - Levels
      - Absent, Reduced or Normal
      - Absent staining: More specific for LGMD 2B than reduced, but present, staining
      - Retained staining: May be related to splice site mutations in dysferlin gene
      - No correlation between level of staining and clinical severity
    - Staining may be patchy among muscle fibers
    - Reduced dysferlin staining: Differential diagnosis
      - Not specific for dysferlinopathy: 30% to 60% with no DYSF mutation
      - Other disorders: CAPN3 (10%); CAV3 (2%); GNE; MYH2; ANO5
  - Dysferlin Western blot
    - Common & specific change in LGMD 2B: Dysferlin reduced to 0% to 20% of normal
    - Absent dysferlin on Western blot: Dysferlin gene mutations very common
    - Good correlation on WB between results in
      - Skeletal muscle (234 kDa) &
      - Monocytes (doublet 224 to 234 kDa)
    - Increased dysferlin expression: Mutatons in exons 36 or 37
  - Other molecules
    - Calpain-3: Reduced especially with C2 domain mutations
    - Sarcoglycans & Dystrophin: Present
    - Aquaporin-4: Reduced
Variant syndromes: Different phenotypes may occur in same family
- General
  - Late in disease course: Varying weakness phenotypes merge
- Distal myopathy: Miyoshi
- Distal myopathy: Distal anterior dysferlinopathy (DMAT;DACM)
  - Onset: Foot drop; Steppage gait
  - Weakness
    - Legs
      - Anterior: Ankle > Knee
      - Distal > Proximal
    - Arms: Proximal
- Myopathy: Proximal + Distal
  - Onset: Proximal weakness; Calf atrophy
  - Weakness: More rapidly progressive
  - Muscle pathology: Inflammation more common
- Myopathy: Later onset, Proximal, Arms > Legs ⁸⁵
  - Mutation: Trp999Cys; Homozygous
  - Onset
    - Age: Mean 38 years; 16 years later than others average
    - Arm symptoms
  - Weakness: Proximal
  - Serum CK: High but lower than average
- Pain syndrome
  - Onset: Distal leg (calf) painful swelling without weakness or atrophy
    - Unilateral or Bilateral
  - No weakness or atrophy
- Asymptomatic with elevated serum CK levels
  - Frequency: 5% of dysferlinopathies
  - Mutations: Missense or Stop
  - Age: 28 & 50 years
  - MRI: Mild gastrocnemius pathology
- Dysferlinopathy: Congenital myopathy ⁷⁰
  - Genetics
    - Mutation: p.Ala927LeufsX21 frameshift
    - Same mutation associated with: Asymptomatic high CK & LGMD syndromes
  - Clinical
    - Onset age: Congenital
    - Weakness
      - Birth: Hypotonia
      - Legs & Neck flexor ± Arms
      - Walking: At 19 to 30 months
      - Motor milestones: Delayed
    - Contractures: Ankles & Hips; Onset 3 years
    - CNS: Normal
  - Laboratory
    - Serum CK: Up to 5000; Normal or mildly high early
    - MRI: Pathology (STIR) in hamstring & gastrocnemius
    - Muscle
      - Myopathic: Fiber size varied; Endomysial connective tissue increased
      - Dysferlin absent; α-dystroglycan normal
- Dysferlin: Mutation carriers ⁷⁴
  - May be symptomatic
  - Mutations: G519R; D625Y
  - Clinical
    - Weakness: Legs; Proximal or Distal; Progressive
    - Calf myalgias: 1 patient
  - Serum CK: High; 600 to 3000
  - Muscle
    - Myopathy
    - Dysferlin expression: Reduced & Patchy
Mouse model: SJL
- Mutation
  - Genomic: 141 bp intronic deletion involving tandem repeat
  - Effects of mutation
    - Alters 3' splicing site
    - Causes deletion of exon 45 in cDNA: 171-bp in-frame deletion
  - Protein results
    - Deletion of 57 amino acids
    - Reduced amount to 15% of normal
- Pathology: Myopathy ± Inflammation
Mouse model: A/J
- Retrotransposon insertion in intron 4 (5' end) of dysferlin gene
- Progressive myopathy: Proximal > Distal
- Perivascular inflammation
- Dysferlin: Absent by Western blot

LGMD R5; Severe Childhood Autosomal Recessive (SCARMD)

● γ Sarcoglycan

; Chromosome 13q12.12; Recessive

Nosology: LGMD2C
γ Sarcoglycan gene
- Promoters: Muscle, Brain & ? Heart-type
- Mutations
  - Many mutations disrupt carboxyl-terminus
  - One Japanese patient with 73 base pair deletion
  - Gypsies: C283Y
  - Tunisia & North Africa: del521-T mutation ³⁶
  - Severe phenotype: May have null or missense mutation
  - Databases: Leiden; HGMD
γ Sarcoglycan protein
- 35 kD Dystrophin-associated glycoprotein
  - Peptide mass: 32 kDa
- Acidic
- Location: Subsarcolemmal
- mRNA expressed
  - Strongly: Skeletal & cardiac muscles
  - Moderately: Lungs, Skin, Spinal cord & Olfactory bulb
  - Weakly: Cerebrum & Aorta
- Sarcoglycan binding: Moderately to β-sarcoglycan
- Homologous sarcoglycan: δ-sarcoglycan
- See: Sarcoglycan complex
Clinical features
- Severity
  - Some with Duchenne-like course
  - Others intermediate between Duchenne & Becker phenotype
  - Mild Becker phenotype in occasional family
  - Variable: Interfamilial; Intrafamilial may be homogeneous or heterogeneous
  - Gypsies with C283Y mutation
    - Early Duchenne-like course but longer survival (50%)
    - Becker phenotype (13%)
    - Overall: More severe than North Africans with out of frame del521-T mutation
- Weakness
  - Onset
    - Mean 5 to 6 years
    - C283Y mutation: < 2 years
  - Proximal > Distal
  - Patchy distribution with some mutations (C283Y)
    - Affected: Glutei, Adductors, Hamstrings, Spinalis, Abdominals, Subscapularis, Soleus
    - Spared: Quadriceps
  - Respiratory: Failure in 3rd decade
- Muscle hypertrophy: Some patients (C283Y); Calf & Tongue
- Hearing loss: Neurosensory
- Cardiac
  - Occasional involvement: Especially late in disease course
  - C283Y mutation: Subclinical; EKG changes 60%; RVH; Diastolic dysfunction
- Skeletal (C283Y): Lumbar hyperlordosis; Scapular winging
- Intelligence: Normal
- Course
  - Loss of ambulation: 10 to 37 years; Mean 16 years
  - No relation between severity of disease & age of onset
  - Death: Common in 2nd decade
Laboratory features
- Serum CK: Very high
- Muscle pathology
  - Myopathic
  - Inflammation: Occasional
  - Sarcoglycan staining
    - Severe disease: Absent γ-sarcoglycan
    - Slowly progressive disease: Reduced γ-sarcoglycan
    - Other sarcoglycans: Levels not related to clinical phenotype
      - α: Normal or reduced
      - δ: Normal or reduced
      - β: Variable; May be reduced most or absent
  - Dystrophin: May be normal or reduced

LGMD R3

● α-Sarcoglycan (Adhalin; SGCA)

; Chromosome 17q21.33; Recessive

Nosology: LGMD 2D
Genetics: α-Sarcoglycan gene
- Promoters: 2
- Mutations
  - Most mutations: Missense: In extracellular domain of SGCA
  - Arg77Cys most common mutation, independent of ethnicity
  - Mutation Databases: HGMD; Leiden
- Allelic disorder: Exercise intolerance
α-Sarcoglycan protein
- 50 kD dystrophin-associated glycoprotein
  - Peptide size: 40.4 kDa
  - Homologous sarcoglycan: ε-sarcoglycan
  - Features distinct from non-homologous sarcoglycans
    - Cadherin-like domain: ? Function by associating with other glycoproteins
    - Calcium-binding pockets
- Sarcoglycan binding: Moderately to β- & δ- sarcoglycans
- Location: Expressed only in skeletal & cardiac muscle
- See: Sarcoglycan complex
- α-Sarcoglycan gene abnormalities
  - May produce absent or reduced level of α-Sarcoglycan in muscle
  - Levels of α-Sarcoglycan correlate roughly with gene structure
    - Null mutations: Often absent α-Sarcoglycan
    - Missense mutations: Reduced α-Sarcoglycan
  - Severity of myopathy correlates best with level of α-Sarcoglycan in muscle
    - Absent α-Sarcoglycan: Duchenne-like phenotype
    - Reduced α-Sarcoglycan: Later onset; Milder weakness
- Other myopathies: α-Sarcoglycan may be reduced in other dystrophies
  - Especially other sarcoglycan disorders
  - Reduced α-Sarcoglycan in muscle (? gene defect): ? Related to dilated cardiomyopathy
Clinical features: Severe or Mild phenotype
- Onset
  - Variable: 2 to 15 years
  - Earlier onset
    - More rapidly progressive weakness
    - Absent α-Sarcoglycan
  - Later onset
    - Ambulation may be preserved
    - Occasional patients with only high CK, but no weakness
    - Reduced but present α-Sarcoglycan
- Weakness
  - Proximal > Distal
  - Symmetric
  - Quadriceps: Severe phenotype
  - Scapular weakness & winging: Severe phenotype
- Calf hypertrophy: Some patients
- Systemic: Rare associated cardiomyopathy
Laboratory features
- Serum CK: Very high; Often > 5,000
- Muscle biopsy
  - Myopathic
    - Fiber size variation
    - Endomysial connective tissue: Increased
    - Degeneration & Regeneration of muscle fibers
    - Myopathic grouping of degeneratiing & regenerating muscle fibers
  - Sarcoglycan staining
    - Absent α-sarcoglycan
    - Other sarcoglycans: Reduced or absent
Treatment: Prednisone inproves motor function (Anecdotal reports)
Heterozygotes (Ile124Thr missense mutation): Some patients have a clinical phenotype ³⁸
- Myalgias
- Scapular winging: 60%
- Calf hypertrophy: 15%
- Serum CK: Normal
- Muscle biopsy: Fiber-size variability; Atrophic fibers; Normal α-sarcoglycan by IHC
α-Sarcoglycan variant disorder: Exercise intolerance & Myalgias ¹⁰¹
- α-Sarcoglycan genetics
  - Inheritance: Recessive
  - Mutations: V247M; R284C
- Clinical
  - Onset age: 1st or 2nd decade
  - Myalgias: With exercise
  - Strength: Normal or Biceps weak
  - Scapular winging
- Laboratory
  - Serum CK: 700 to 12,000; Higher with exercise
  - Muscle pathology
    - Histology non-diagnostic: Atrophic muscle fibers
    - α-Sarcoglycan: Reduced by Western blot
  - EMG: Normal

LGMD R4

● β-Sarcoglycan

; Chromosome 4q12; Recessive

Nosology: LGMD 2E
Epidemiology: Common in Northern & Southern Indiana Amish; Bern, Switzerland
β-Sarcoglycan gene
- Promoters: 1
- Mutations
  - Missense: Common
  - Common mutation: Ser114Phe
  - Also: Nonsense, Insertion & Deletion
- Databases: Leiden; HGMD
β-Sarcoglycan protein
- 43 kD dystrophin-associated glycoprotein
  - Peptide size: 34.8 kDa
  - Binds to β-dystroglycan by extracellular domain
- Sarcoglycan binding: Strongly to δ; Moderately to γ
- Location: Subsarcolemmal
- Expression patterns
  - Muscle: Skeletal & Cardiac
  - Only sarcoglycan expressed outside muscle: Brain; Kidney
- See: Sarcoglycan complex
Clinical features: Severe; Occasional mild phenotype
- Onset age
  - < 3 years to Teens
  - Teen onset: Similar to "outlier" dystrophinopathy
  - Intrafamilial variability
- Myopathy
  - Proximal weakness
  - Muscle hypertrophy: Prominent; ± Tongue
  - Shoulders: Scapular winging; Muscle wasting
  - Progression: Often in wheelchair by 10 to 15 years, usually by 25 years
- Cardiomyopathy
  - Occasional patients
  - Mutation: 8 bp duplication in exon 3 of 1 allele
Laboratory features
- Serum CK: High; Often > 5,000
- Muscle biopsy
  - Myopathic
  - Sarcoglycans: All usually absent or markedly reduced
  - Dystrophin: Often reduced but not absent
- Cardiac muscle: Sarcoglycans reduced with cardiomyopathy
β-Sarcoglycan knockout mouse
- Myopathy with muscle hypertrophy
- Cardiomyopathy with focal areas of necrosis
- Reduced Sarcoglycan-sarcospan complex in vascular smooth muscle: Vascular δ in heart, diaphragm & kidneys

LGMD R6

● δ-Sarcoglycan (SGCD)

; Chromosome 5q33.3; Recessive

Nosology: LGMD 2F
δ-Sarcoglycan gene
- Promoters: 3; 1 predominantly in skeletal muscle
- Mutations
  - Frameshift ® Premature truncation of protein: del656C: African-Brazilian ancestry
  - Missense: Glu262Lys (Near cysteine-rich region)
  - Nonsense ® Premature truncation of protein: E93Ter; Arg165Ter; Trp30Ter
  - Databases: HGMD; Leiden
- Allelic with
  - Dilated cardiomyopathy 1L (CMD 1L)
  - LGMD, Mild phenotype
δ-Sarcoglycan protein
- 35 kD dystrophin-associated glycoprotein
- Basic
- Location: Subsarcolemmal
- Sarcoglycan binding: Strongly to β- & γ- sarcoglycans
- Homologous sarcoglycan: γ-sarcoglycan
- See: Sarcoglycan complex
Clinical: Severe phenotype with most mutations producing myopathy
- Onset: 2 to 10 years
- Weakness: Proximal; Symmetric
- Other muscle change: Calf hypertrophy; Cramps
- Progression: Wheelchair 9 to 16 years in most; One patient walking at 19 years
- Death: 9 to 19 years
- Intelligence: Normal
- Cardiac
  - Often Normal
  - Dilated cardiomyopathy described : May occur without skeletal myopathy
Laboratory features
- Serum CK: High; 10x to 50x normal
- Muscle biopsy
  - Myopathic: Degeneration & regeneration of muscle fibers
  - Immunostaining
    - δ-Sarcoglycan: Absent
    - Other sarcoglycans: α & β absent; γ reduced or absent
    - Dystrophin: Present but reduced
Animal model
- Syrian hamster cardiomyopathy: Deletion in promoter region of δ-Sarcoglycan gene
- Boston terrier dogs: LGMD syndrome
SGCD variant: LGMD, Mild phenotype

LGMD R7

● Telethonin (Titin-Cap; TCAP)

; Chromosome 17q12; Recessive

Nosology: LGMD 2G
Epidemiology: Brazil (Italian ancestry) & Europe
Genetics
- Mutations
  - Point mutations or small deletions
  - Produce stop codons
  - Ser11* (c.32C>A; Dravidian families); Trp25X (Bulgarian Muslims); Gln35X; g.637-640del2
- Allelic with
  - Dilated cardiomyopathy 1N (DCM 1N): ? Polymorphism
  - Congenital muscular dystrophy with joint contractures
  - Hypertrophic cardiomyopathy 25 (CMH 25): Dominant; Missense mutations
  - Distal myopathy
Telethonin (Titin-Cap) protein

Telethonin in muscle fibers
- Function
  - Substrate of serine kinase domain of titin
  - Titin phosphorylates C-terminal domain of telethonin
    - Occurs in early differentiating myocytes
- Tissue localization: Cardiac & Skeletal muscle; GI smooth muscle
- Cellular localization: Sarcomeric Z-disc
Clinical features
- Onset
  - Age: Mean 12 to 18 years; Range 1 to 25 years
  - Gait disorder: Toe walking
- Weakness:
  - Extremities: Legs > Arms
    - Legs
      - Proximal: Glutei; Hamstrings; Hip adductors
      - Distal: Foot drop; Some patients
    - Arms: Proximal
    - Asymmetry: Some patients
  - Face: Normal or mildly weak
  - Neck: Normal
  - Progression: Slow; 40% non-ambulatory in 3rd or 4th decade
- Muscle size
  - Calf hypertrophy 50%
  - Calf atrophy 50%
- Discomfort: Occasional patient
  - Cramps
  - Myalgias
- Cardiac involvement 55%
- Contractures: Ankles
Laboratory
- Serum CK
  - Increased 3- to 30-fold
  - Lower with greater age
- Muscle imaging
  - More involvement: Quadriceps; Anterior tibial; Posterior pelvic
  - Asymmetry: Some
  - Preservation: Adductor longus; Biceps femoris
  - Hypertrophy: Sartorius; Gracilis
- EMG: Small myopathic potentials ± Large potentials
- Muscle pathology
  - Myopathic: Degeneration & Regeneration
  - Rimmed vacuoles: Some patients
  - Lobulated muscle fibers: Especially type 1
  - Cytoplasmic bodies
  - Telethonin protein: Absent from muscle
Variant telethonin syndrome: Congenital Muscular Dystrophy ⁸⁰
- Epidemiology: French male
- Genetics
  - TCAP mutation: Gln58X; Homozygous
  - Inheritance: Recessive
- Clinical
  - Motor
    - Milestones: Delayed head control & sitting
    - Weakness
      - Proximal (Psoas; Adductors) > Distal
      - Anterior tibial
      - Neck flexion
      - Course: Minimal progression
    - Gait: Waddling; Falling
    - Muscle size: Glutei wasting; Calf hypertrophy, mild
  - Skeletal
    - Scapular winging
    - Scoliosis
    - Joint laxity: Distal arms
    - Contractures: Ankles
  - Heart: Normal
- Laboratory
  - Pathology: Muscle
    - Fiber size: Varied
    - Internal nuclei
    - Necrosis & Regeneration: Some clusters
    - Type I fibers: Small
    - Telethonin: Absent
    - α-Dystroglycan: Normal
  - Serum CK: 600 to 1300
TCAP variant: Distal myopathy ¹¹⁷
- Epidemiology: 1 patient
- Genetics
  - Inheritance: Recessive
  - Mutation: Homozygous; Stop; c.256C>T
- Clinical
  - Onset age: 50 years
  - Weakness
    - Symmetric
    - Legs: Distal > Proximal; Anterior > Posterior
    - Arms: Normal
- Laboratory
  - Serum CK: < 300
  - EMG: Myopathic
  - Muscle MRI: Involvement of adductors & hamstrings
  - Muscle: Vacuoles; Varied fiber size

LGMD R8: Manitoba Hutterite Dystrophy

¹¹³
● Tripartite-motif containing gene 32 (TRIM32)

; Chromosome 9q33.1; Recessive

Nosology: LGMD 2H
Epidemiology
- Focus: Hutterite
- Other: 16 patients
Genetics: Mutations
- Homozygous for D487N point mutation
  - All Hutterite patients
  - Mutation localized in NHL domain
- Other mutations: Deletions, Frameshift, Nonsense
- Same gene as
  - Sarcotubular myopathy: Same D487N mutation
  - Bardet-Biedl syndrome 11
Protein
- Function
  - E3-ubiquitin ligase
  - Labeling of proteins with ubiqutin for proteasome degradation
- Homo-multimer: Self-association via CC regions
- Concentrated in cytoplasmic & nuclear bodies
- Tissue localization: Muscle; Testis; Heart; Skin
Clinical
- Variable phenotype
- Onset
  - Age: 3 to 45 years; Usual 2nd or 3rd decade; Some asymptomatic in 3rd decade
  - Proximal weakness; Back pain; Fatigue; Gait change
- Weakness
  - Proximal leg: Quadriceps & Pelvic girdle
  - Some patients with: Axial, Face, Periscapular, Distal arm weakness
  - Mild
  - Respiratory: Often spared
  - Progression: Slow; Ambulatory > 50 years of age
- Heart: Not involved
Laboratory
- Serum CK: High; 250 to 4,500 U/L
- EMG: Myopathic
- Muscle MRI
  - Thigh: Posterior > Anterior
  - Lower leg: Posterior; Anterior tibial; Peronei
Muscle biopsy: Mild dystrophic changes
- Fiber size variation
- Muscle fiber degeneration & regeneration
- Other: Fiber splitting; Internal nuclei
- Endomysial fibrosis
- Vacuoles: Few patients

Sarcotubular myopathy ⁴⁶
● Tripartite-motif containing gene 32 (TRIM32)

; Chromosome 9q31-q33; Recessive

Epidemiology
- Hutterite brothers from South Dakota
- Non-Hutterite brothers from Germany
Genetics
- Same mutation as LGMD 2H: Homozygous missense (D487N)
Clinical
- Onset: Congenital, Childhood or Adult (31 years)
- Weakness
  - Proximal: Symmetric; Mild
  - Face: Mild
- Muscle size
  - Hypertrophy: Calf
  - Atrophy: Proximal
- Myalgias: Exercise induced
- Scapular winging
- Tendon reflexes: Normal or Reduced
Pathology
- Vacuoles
  - Multiple small rounded
  - In type 2 > type 1 fibers
  - Sarcoplasmic reticulum membranes
- Varied fiber size
- Z-disk streaming

LGMD R9 (MDDGC5)

¹⁸
● Fukutin-related protein gene (FKRP)

; Chromosome 19q13.32; Recessive

Nosology
- LGMD 2I
- Muscular dystrophy-Dystroglycanopathy
Epidemiology
- > 40 familes
- Carrier risk: ~ 1:400
- Common in Denmark & parts of England
Genetics
- Point mutations most common: Missense
- Common mutation in 1 allele (> 90%): Leu276Ileu (C826A)
- Disease severity correlates with mutation in 2nd allele
- Leu276Ileu homozygosity correlates with less severe phenotype
- Allelic with
  - Congenital muscular dystrophy with muscle hypertrophy & Normal CNS (MDC1C)
  - Myopathy with abnormal merosin (Laminin-2)
  - Walker-Warburg syndrome: Homozygous FKRP mutations; Met1Val & Cys318Tyr
FKRP protein
- Ubiquitous
- Highest levels: Skeletal muscle; Heart; Placenta
- Subcellular
  - Golgi
  - Skeletal and cardiac muscle
    - Surrounds myonuclei
    - No change in location with disease mutations
    - Absent from the nuclei of interstitial cells
  - Targeted by N-terminus & tm domain
  - Not secreted
- Glycosyltransferase
- Colocalizes with α-Mannosidase II
- Associated with dystroglycan processing
Clinical
- Onset
  - Age
    - Range 0.5 to 27 years; 61% less than 5 years
    - Birth in patients with Congenital muscular dystrophy syndrome (MDC1C)
  - Weakness: Waddling gait; Difficulty with stairs; Hypotonia
- Weakness
- Muscle size
  - Wasting: In regions of weakness; Arms > Legs
  - Hypertrophy: Calves 77%; Thighs; Tongue
- Other occasional muscle features
  - Exertional pain: Early symptom,: Mean 14 years, Range 2 to 45 years
  - Cramps: Limbs & Tongue described
  - Myoglobinuria (25%)
    - Multiple episodes
    - Related to physical activity
    - Can occur at time with mild or no weakness
    - Frequent in patients with homozygote common mutation (Leu276Ileu)
- Tendon reflexes: Preserved; Knee mildly reduced
- Intellect: Normal
- Skeletal
  - Contractures: Often at ankles; More common in non-ambulant patients
  - Scoliosis
- Cardiomyopathy
  - Common: 30% to 80%; Often seen on echocardiography
  - Type: Dilated
  - Usually mild
  - Left ventricular failure
  - May be isolated feature: Homozygous C826A mutation
  - No relation to skeletal muscle severity
- Skin: May be soft or hyperextensible
- Variable severity
  - Severe: Onset < 2 years; Never run; Lose ambulation in teens
  - Milder: Later onset; Cramps; Muscle hypertrophy
  - Consistent phenotype within individual families
Laboratory
- Serum CK: Very high; 1,000 to 8,000
- Muscle biopsy
- Nerve conduction studies: Normal
- EKG: Normal
- MRI: Normal CNS or minimal atrophy

Myopathy with abnormal merosin (Laminin-2)

⁴
● Fukutin-related protein gene (FKRP)

; Chromosome 19q13.3; Recessive

Genetics: Allelic with LGMD 2I
Clinical
- Onset
  - Usually adult: 11 to 40 years
- Female preponderance
- Weakness
  - Cranial: Eye closure; Neck flexion
  - Upper extremity: Proximal; No scapular winging
  - Lower extremity: Especially hamstrings + hip adductor & flexors
  - Vital capacity: Reduced to 30% to 93% of normal
  - Asymmetry: Some
  - Progressive
- Muscle hypertrophy: Calves; Brachioradialis
- Cramps: Occasional
- Skeletal: Lumbar lordosis; No contractures
- CNS (MRI) & cardiac: Normal
Laboratory
- Serum CK: 1,100 to 3,700
- EMG: Myopathic
- Muscle histology
  - Variation in fiber size
  - Muscle fiber necrosis
- Muscle merosin
  - Normal immunocytochemistry of muscle section (80 kDa & 300 kDa fragments)
  - Absent on Western blot

LGMD R10

● Titin

; Chromosome 2q31.2; Recessive

Nosology: LGMD 2J
Genetics
- Mutations
  - Homozygous or Compound heterozygous for titin mutations
  - Mutation types
    - 11 bp insertion-deletion (Finnish; FINmaj): Final exon (363)
    - Missense: Leu293,356Pro (French)
    - Common patterns
      - Homozygous: Exon 364 mutations
      - Compound heterozygous: Exon 364 + Truncating mutation
  - Genotype-Phenotype corelations
    - Homozygous 11 bp deletion: Severe, Childhood onset
    - French missense mutation: Onset 3rd decade, Proximal Arms
  - Disease relevance of mutations: General ¹¹⁰
    - Truncating mutations most strongly associated with myopathy
    - Biallelic truncating mutations
      - Primary cardiac common
      - Wide range of phenotypes
    - Single heterozygous truncating mutations
      - Skeletal muscle disorders common
      - Also associated with: Dominant dilated cardiomyopathy
      - Western blot analysis: May identify further truncating variants in trans
- Allelic disorders
  - Dominant
    - Distal myopathy, Finnish (Tibial MD)
    - Myopathy with Early Respiratory failure (HMERF)
      - Cytoplasmic aggregate myopathy
      - Cytoplasmic body myopathy
    - Dilated cardiomyopathy 1G
    - Hypertrophic cardiomyopathy (CMH 9)
  - Recessive
Titin protein
Clinical
- Usually occurs in families with other members having dominant distal weakness syndrome
- Onset age
  - Usual: Childhood
  - Range: < 10 years to 3rd decade
- Weakness
  - Proximal > Distal
  - More severe than in allelic distal myopathy
  - Face: Normal
  - Asymmetric: Some patients
- Wasting: Anterior tibial
- Progression
  - Usual: Wheelchair < 30 years, within 20 years of onset
  - Some patients ambulatory at 60 years
- No cardiomyopathy
Laboratory
- Serum CK: High
- Muscle biopsy
  - Myopathic
  - No vacuoles
  - Loss of calpain-3
  - Western blot: Severely reduced C-terminal titin fragments
  - Obscurin: Mislocalization
Titin variant syndrome: Proximal adult-onset rimmed vacuolar myopathy
- Genetics
  - Inheritance: Recessive
  - Mutations: Compound heterozygous; Exon 364 + Missense
- Clinical
  - Onset age: Adult
  - Weakness: Quadriceps & Soleus; Tibial spared
- Laboratory
  - Muscle: Rimmed vacuoles
Titin variant syndrome: Emery-Dreifuss syndrome without cardiac involvement ¹⁰²
- Epidemiology: 3 families; French & Algerian
- Genetics
  - Inheritance: Recessive
  - Mutations: Truncating; Mex3 exon in sarcomeric M-band
- Titin protein
  - Mutated protein: Truncation of M-line
- Clinical
  - Onset age: 3 to 10 years
  - Weakness
    - Limb-Girdle: Proximal > Distal
    - Respiratory: Vital capacity reduced in some (67%)
    - Trunk: Scapular winging; Abdominal
    - Symmetric
    - Course: Progressive to wheelchair by 13 to 36 years
  - Large muscles: Calf; Tongue
  - Contractures
    - Arms & Legs
    - Proximal & Distal
    - C-spine & Masseter in some
  - Cardiac: Normal
- Laboratory
  - Serum CK: 1.5x to 10x high; Lower with increased age
  - EMG: Myopathic
  - Muscle pathology
    - Fiber size: Varied
    - Necrosis: Scattered
    - Immature muscle fibers
    - Internal nuclei
    - Internal architecture: Irregular
    - Rimmed vacuoles
    - Rods or Cytoplasmic bodies
    - Calpain-3: Absent or very reduced
    - Ultrastructure: M-bands abnormal
  - Muscle MRI: Posterior thigh, Gastrocnemius & Glutei most involved
Titin variant syndrome: Distal myopathy ¹⁰⁹
- Epidemiology: Serbian families
- Genetics
  - Inheritance: Recessive
  - Mutations
    - General: Stop-gain variants
    - Common: c.107635C4T (p.Gln35879Ter); Founder mutation
    - Other: Stop codons in TTN exons 286 to 358
  - Allelic disorders
- Titin protein
- Clinical: Similar to Dominant Finnish Tibial MD
  - Onset: Adult; 14 to 44 years
    - Later onset: Founder mutation, homozygous
  - Weakness
    - Distal (100%) > Proximal (60%)
    - Legs > Arms: Foot & toe dorsiflexors > plantarflexors
    - Proximal involvement: Hip & shoulder girdle
    - Asymmetry: 30%
    - Scapular winging: 40%
    - Course: Most patients remain ambulant
  - Contractures: Ankle
  - Respiratory: Normal
  - Cardiomyopathy: Uncommon
- Laboratory
  - Serum CK: Normal to Mildly high
  - EMG: Myopathic
  - Muscle MRI: Similar to Tibial MD, Dominant
  - Muscle biopsy: Dystrophic
    - Muscle fibers: Hypertrophic; Atrophic
    - Endomysial connective tissue: Increased
Titin variant syndrome: Lethal congenital contracture syndrome (LCCS) ¹¹¹
- Epidemiology: 1 family
- Genetics
  - Mutations: Homozygous c.36122delC (p. P12041Lfs*20) variant (In exon 167 in fetal IC isoform of TTN)
  - Inheritance: Recessive
- Clinical
  - Intrauterine: Reduced movement; Death
  - Neonatal respiratory distress
  - Spontaneous movement: Reduced
  - Contractures: Large joints
  - Death: < 17 weeks
- Laboratory
  - Bone: Multiple fractures
Mouse model: Homozygous knockout
- Severe: Lethal
- Weakness: Distal > Proximal

LGMD R11 (MDDGC1) : with Mental retardation and Reduced α-dystroglycan ⁴⁵
● O-mannosyltransferase 1 (POMT1)

; Chromosome 9q34.13; Recessive

Nosology
- LGMD 2K
- MDDGC1: Muscular dystrophy-Dystroglycanopathy
Epidemiology: 15 patients
Genetics
- Mutations: Missense mutations most common; Turkish Ala200Pro
- Allelic disorders
  - Walker-Warburg syndrome: MDDGA1
  - Disease related mutations: > 76
POMT1 protein
- Clinical phenotype severity: Inversely correlated with POMT1 activity
Clinical
- Onset
  - Ages: 1 to 33 years
  - Motor: Fatigue; Difficulty climbing stairs & running; Early milestones normal
- Muscle
  - Size: Mild pseudohypertrophy
  - Weakness: Proximal
  - Course: Slow progression
- Skeletal
  - Joint contractures (50%): Ankles
  - Scoliosis
- CNS (60%)
  - Mental retardation, IQ 50 to 76
  - Microcephaly
- Cardiomyopathy (30%): LV dilatation
Laboratory
- Serum CK: Very high (9x to 40x elevated)
- Muscle
  - Fiber size: Varied
  - Fibeer types: 1 predominance
  - Cores: Some patients
  - α-Dystroglycan: Reduced glycosylation
- MRI: Normal CNS

LGMD R12

⁶⁷
● Anoctamin 5 (ANO5, TMEM16E, GDD1)

; Chromosome 11p14.3; Recessive

Nosology: LGMD 2L
Epidemiology
- May be 10% to 20% of LGMD families
- Females: Less commonly or less severely affected
Genetics
- Mutations: > 20 identified
  - Splice site (C1295G; Aberrant splicing of Exon 13)
  - Duplication (c.191dupA (p.Asn64Lysfs*15) in exon 5): Common in Northern Europe
  - Arg758Cys in exon 20: Common mutation
  - Missense: G231V in exon 8
  - Locations: Distributed all along gene
- Allelic with
  - Gnathodiaphyseal dysplasia : Dominant
  - Distal myopathy (MMD3): Recessive
- Genotype-Phenotype correlations
  - Variable phenotypes, mild & severe, with most mutations
Anoctamin 5 protein
- Member of family of proteins with 8 transmembrane domains
  - Anoctamins 1, 2 &3 are calcium-activated chloride channels (CaCC)
  - ANO3 mutatins cause: Dominant Craniocervical Dystonia (DYT23)
- Integral membrane glycoprotein
- Intracellular
- Functions: Myogenesis; Osteogenesis
- Mutations may cause: Defective membrane repair
Clinical
- Variability
  - Intrafamilial: Prominent
  - Variant syndromes
    - Distal myopathy
    - Normal strength with high CK
- Onset
  - Age: Mean = 33 to 43 years; Range 11 to 51 years
  - Weakness: Quadriceps, Asymmetric
- Muscle
  - Atrophy: Quadriceps; Biceps brachii; Lower leg
  - Asymmetric
  - Weakness
    - Legs > Arms
    - Scapular: Biceps
    - Pelvic: Psoas; Quadriceps
    - Posterior leg: See MMD3
    - Distal arms: Normal strength
    - Face: Few patients
    - Progression: Slow
  - Muscle pain: 86%; 50% with, or after, exercise
  - Fatigue: May occur before weakness
  - Calf hypertrophy or atrophy: Some patients
  - Rhabdomyolysis: Occasional patient
  - Course: Progressive; Walking retained
  - Respiratory: Normal or Mild changes
- Contractures: Unusual
- Cardiac
  - Atrial: Arrhythmias; Bradycardia; Some patients
  - Cardiomyopathy: Dilated or Hypertrophic
Laboratory
- MRI: Early atrophy of medial quadriceps, hamstrings & adductor magnus
- Serum CK: Normal to 35,000
- EMG: Myopathic; Some with spontaneous activity or myotonia
- MRI: Asymmetric involvement
Pathology: Muscle
- Muscle fibers
  - Size: Varied
  - Necrosis & Regeneration
  - Internal nuclei
  - Splitting
  - Internal architecture: Irregular; Whorled
  - Vacuoles: 2 patients
  - Ultrastructure: Multifocal sarcolemmal lesions
- Endomysial connective tissue: Increased
- Inflammation: In severe cases; Endomysial
- Amyloid
  - Frequency: 50%
  - Location: Peri-Vascular & Muscle fiber
  - No relation to mutation location or clinical features
- Dystrophy proteins
  - Dystrophin reduced: 40%
  - Calpain-3 reduced: 45%
  - Dysferlin: Normal
ANO5 Variant syndrome: Distal Miyoshi-like myopathy 3 (MMD3)
- Epidemiology: Dutch & Finnish families
- Genetics
  - Inheritance: Recessive
  - ANO5 Mutations
    - Missense: Arg758Cys in exon 20
    - Duplication (c.191 dupA in exon 5)
  - Allelic with: LGMD 2L
- Clinical
  - Onset
    - Age: 2nd & 3rd decade
    - Difficulty running & standing on toes
  - Weakness
    - Calf: Early; Difficulty running & walking on toes
    - Proximal: Ileopsoas; Hamstrings, Gluteus maximum, Hip adductors
  - Hypertrophy: Calf; Extensor digitorum brevis
  - Muscle discomfort: Calves
  - Asymmetry
- Laboratory
  - Serum CK: 1,500 to 16,000
  - Muscle pathology
    - Cell membrane repair defect
  - Imaging: Medial gastrocnemius & soleus involvement
ANO5 Variant syndrome: Normal strength + High serum CK ¹⁰⁶
- Epidemiology: Males & Females
- Clinical
  - Myalgias
  - Exercise intolerance
  - Calf: Hypertrophy or Atrophy
  - Some patients asymptomatic
  - Course: May remain with few, or mild, symptoms for long periods
- Laboratory
  - Serum CK: High; 200 to 40,000 U/L; Vary over time
  - EMG: May be normal or myopathic
  - Muscle imaging: Medial gastrocnemius involved (55%)
  - Muscle biopsy: Non-specific or Normal

LGMD R13 (MDDGC4)

⁵⁹
● Fukutin (FCMD; FKTN)

; Chromosome 9q31.2; Recessive

Nosology
- LGMD 2M
- Muscular dystrophy-Dystroglycanopathy
Epidemiology: 5 families; Portuguese, Turkish, French, Israeli Jewish & Indian
Genetics
- Mutations
  - Types: Stop & Missense
  - 1167dupA; 1363delG; Arg47X; Ala170Glu; Arg246Gly; Arg307Gln; Tyr371Cys
- Allelic disorders
Clinical
- Onset
  - Age: Less than 6 months
  - Hypotonia
  - Motor delay
  - Deterioration with acute febrile illness
- Weakness
  - General: Diffuse; Variable severity
  - Distribution: Axial & Proximal > Distal
  - Legs > Arms
  - Face: Mild to Moderate
  - Improves with corticosteroid treatment
  - Many patients ambulant
  - Course: Progressive
- Muscle size
  - Wasting: Most muscles
  - Hypertrophy: Posterior leg ± Tongue & other
- CNS
  - Normal in mildest patients
  - Reduced intelligence: Variable association with degree of weakness
- Skeletal
  - Spinal rigidity
  - Joint contractures
- Cardiomyopathy: Some patients
Laboratory
- Serum CK: Very high
- Muscle biopsy
  - Morphology: Dystrophic; Muscle fiber necrosis
  - Endomysial connective tissue: Increased
  - Glycosylated α-dystroglycan: Nearly absent
  - Laminin-α2, β1 & γ1: Mildly reduced
- MRI: May show cortical & posterior fossa pathology
  - Vermis hypoplasia
  - Polymicrogyria

Myopathy, Early-onset with Ophthalmoplegia ⁷⁸
● Myosin, heavy chain 2, skeletal muscle, adult (MYH2)

; Chromosome 17p13.1; Recessive

Epidemiology: 5 families from UK & Finland
Genetics
- Compound heterozygous
- Mutation type: Truncating
- Allelic disorders
MYH2 protein
- Myosin subtype
- Location: Type 2A muscle fibers
Clinical
- Onset age: Early childhood
- Weakness
  - Generalized
  - Mild
  - Proximal > Distal
  - Face & Neck
  - Extraocular muscles
    - Severe ophthalmoplegia
    - Ptosis 20%
  - Prognosis: Slow progression with age
- Muscle wasting
- Joints: Hypermobility
Laboratory
- Muscle pathology
  - Type 2A fibers: Absent
  - Fiber size: Varied
  - Internal nuclei
  - Endomysial connective tissue: Increased
- EMG: Myopathic
- Serum CK: Normal
- Muscle imaging: Selective nvolvement of
  - Leg: Medial gastrocnemius
  - Thigh: Semitendinosus, Gracilis & Vastus lateralis
Also see: Myopathies with Ophthalmoplegia

Early-onset Myopathy with External ophthalmoplegia ⁷⁸
● Myosin, heavy chain 2, skeletal muscle, adult (MYH2)

; Chromosome 17p13.1; Recessive

Nosology: Same as MYH2 mutations
Epidemiology: Israeli-Arab inbred families
Genetics
- MYH2 mutation: c.2400delG in exon 19
- Allelic disorders
- Variant syndrome: Juvenile-onset myopathy with PEO
Clinical
- Onset age: Early childhood
- Ocular: External ophthalmoplegia (100%)
  - Conjugate
  - Non-restrictive
  - Impairment greatest in upgaze
  - No ptosis or aberrant eye movements
- Weakness
  - Symmetric
  - Severity: 4/5
  - Face: Mild; Eyes > Mouth
  - Voice: Nasal
  - Neck: Flexors (100%)
  - Limbs
    - Proximal arms: Most common (75%)
    - Distal arms (50%)
    - Proximal legs (30%)
    - Distal legs: Normal
  - Associated with wasting
  - Progression: Slow
- Skeletal
  - Face: Dysmorphism
  - Scoliosis (73%)
Laboratory
- Orbital MRI: Fatty replacement of oculorotatory muscles
- EMG: Myopathic (50%)
- Serum CK: Usually normal; Occasional <2x normal in younger patients
Muscle biopsy
- Muscle fiber types
  - Type 1 muscle predominance
  - Type 2A absent
- Core-like changes

MYH2 variant syndrome: Juvenile-onset myopathy with PEO ⁹⁷
- Epidemiology: Australian patient
- Genetics
  - Mutation: c.5630T>C, p.(Leu1877Pro)
  - Inheritance: Sporadic
- Clinical
  - Onset age: 16 years
  - Weakness
    - Distal: Hands most severe; Feet
    - Proximal: Hip & knee flexion
    - Scapular winging
    - Bulbar: Hypophonia; Palatal movements reduced; Dysphagia
    - Face
    - Respiratory
  - Eyes
    - Ophthalmoplegia: Progressive to severe with some preserved downgaze
    - Ptosis
  - Atrophy: Upper extremities
  - Tendon reflexes: Absent proximally
  - Contractures: Ankles
- Laboratory
  - EMG: Myopathic
  - Serum CK: 153 to 806
  - Muscle MRI
    - Extensive fat replacement
    - Relative sparing: Deltoid & Anterior legs
  - Muscle
    - Fiber size: Varied; Small to Hypertrophy
    - Internal nuclei
    - Endomysial fibrosis. Dystrophic features were present, being
    - Lobulated fibers & Core-like structures
    - Fiber types: Most type 1, Few small type 2
    - Dystrophy related protein staining: Normal
    - No vacuoles

Myosclerosis (LGMD R22)

⁶⁹
● Collagen, type VI, subunit α2 (COL6A2)

; Chromosome 21q22.3; Recessive

Epidemiology: 1 family
Genetics
- Mutation: Q819X; Homozygous
- Allelic disorders
Clinical
- Onset
  - Age: Childhood; 2 to 4 years
  - Contractures
- Weakness
  - Distribution: Proximal + Distal
  - Severity: Mild to Moderate
  - Vital capacity: Reduced
- Contractures
  - All joints: Limbs; Jaws; Spine
  - Progressive
  - No hypermobility
Laboratory
- Serum CK: Mildly high (1.5x)
- Muscle biopsy
  - Endomysial connective dissue: Diffusely increased
  - Muscle fibers
    - Size: Varied
    - Internal nuclei
    - Laminin β1: Reduced on extrajunctional basal lamina
    - Collagen VI
      - Discontinuous on muscle basal lamina
      - Absent from capillaries
      - Reduced on Western blot
  - Ultrastructure
    - Basement membrane defects: Thickening & Duplication
    - Pericytes: Increased numbers

Limb Girdle Dystrophy with Mental Retardation (MDDGC9; LGMD R16)

⁷⁹
● Dystrophin-associated glycoprotein 1 (Dystroglycan 1; DAG1)

; Chromosome 3p21.31; Recessive

Nosology: LGMD 2P
Epidemiology: Turkish & British families
Genetics
- Mutation: Thr192Met; Homozygous
- Mutation in 1 patient of original series
- Allelic disorders
  - Asymptomatic high CK
  - Congenital muscular dystrophy MDDGA9
DAG 1 protein
- Mutation: Alters DAG1 glycosylation & interaction with LARGE
Clinical
- Onset
  - Age: 1st decade
  - Fatigue
  - Weakness: Stairs; Running
- Muscle
  - Weakness: Proximal > Distal
  - Size: Normal or Mild increase in thigh or calves
  - Progression: Slow: Patients remain ambulant
- Contractures: Ankles (50%)
- CNS
  - Mental retardation: Mild to severe
  - Head size: Small
Laboratory
- Serum CK: Very High
- Muscle
  - Fiber size: Varied
  - Regeneration & Occasional necrosis
  - Endomysial connective tissue: Increased
  - α-Dystroglycan: Reduced
- Brain MRI: Normal

DAG1 variant syndrome: High CK, Asymptomatic ⁹⁶
- Epidemiology: 1 patient
- Mutations: c.220G>A (Val74Ile) & c.331G>A (Asp111Asn)
- Clinical
  - Strength: Normal
  - Pseudohypertrophy: Calf
- Laboratory
  - Serum CK: 1,855 to 6,512
  - Muscle
    - Fiber size: Varied
    - Regenerating fibers: Few
    - Internal nuclei
    - Endomysial fibrosis: Mild
    - α-Dystroglycan: Reduced glycosylation
  - Muscle CT
    - Low intensity: Rectus femoris, Semimembranosus, Gastrocnemius
DAG1 variant syndrome: Congenital muscular dystrophy MDDGA9
- Epidemiology: 2 families, Israeli-Arab & Libyan
- Genetics
  - Inheritance: Recessive
  - Mutations: Homozygous; Cys669Phe, 1-BP del, 743C
- Clinical
  - Onset: Congenital
  - CNS: Developmental delay; Mental retardation
  - Eye: Cataract, Retinal dystrophy, Myopia, Buphthalmos
  - Motor: Hypotonia; Reduced movements; Respiratory failure
  - Death: Infancy; Respiratory failure
- Laboratory
  - Serum CK: High, 800 to 2,000
  - Muscle: Fiber size varied; α- & β-dystroglycan absent
  - Brain MRI: Brainstem kinking; Cerebellar vermis atrophy; White matter cysts;
    Hydrocephalus; Polymicrogyria; Corpus callosum thin; Calcifications

LGMD R18: Limb Girdle Dystrophy with Movement Disorder & Intellectual Disability

⁸⁹
● Transport (Trafficking) protein particle complex, Subunit 11 (TRAPPC11)

; Chromosome 4q35.1; Recessive

Nosology: LGMD 2S
Epidemiology: Syrian, Turkish, Han Chinese & Hutterite families
Genetics
- Mutations
  - Missense, Deletion or Splice site
  - Gly980Arg (Syrian); Ala372_Ser429del (Hutterite); c.661-1G>T, splice site
TRAPPC11 protein
- TRAPP multisubunit tethering complex
- Function: ER to Golgi vesicle trafficking (ERGIC)
- Expression: Ubiquitous
- Mutations
  - Disrupt Golgi apparatus architecture
  - Slow exit of proteins from Golgi to cell surface
  - LAMP1 & LAMP2: Abnormal; Increased glycosylation
Clinical
- Myopathy (60%)
  - Onset: Infant or Childhood
  - Proximal
  - Legs > Arms
  - Face: Mildly myopathic
  - Scapular winging: Mild
  - Discomfort: Myalgia; Cramps
  - Fatigue
  - Progressive: Reduced ambulation
- CNS
  - Intellectual disability: Moderate; Global or Motor delay
  - Variable features
    - Seizures
    - Ataxia: Truncal
    - Leg spasticity
    - Hyperkinetic movements
      - Infantile onset
      - Choreiform, Athetoid or Dystonia
    - Tendon reflexes: Reduced
- PNS: Variable
  - Tendon reflexes: Reduced
  - Autonomic: Alacrima; Achalasia
- Skeletal
  - Hip dysplasia
  - Scoliosis
- Systemic: Variable among families
  - Cardiac: Usually normal
  - Eye: Cataracts, infantile-onset; Strabismus
  - Hepatomegaly with steatosis
Laboratory
- Serum CK: High in 100%; 300 to 9000
- Brain MRI: Normal or Mild cerebral or cerebellar atrophy
- Muscle
  - Myopathic
    - Fiber size: Varied
    - Necrosis & Regeneration
    - Internal nuclei
    - Endomysial connective tissue: Increased
    - Lipid increased: 1 family
    - α-Dystroglycan: Normal or Reduced
  - Neuropathic: Fiber type grouping in 1 family
- Muscle MRI: Gluteal & Posterior leg muscle involvement

Other Dominant Myopathies

Bethlem myopathy

: Several loci
● Collagen, type VI, subunit α1 (COL6A1)

; Chromosome 21q22.3; Dominant
● Collagen, type VI, subunit α2 (COL6A2)

; Chromosome 21q22.3; Dominant or Recessive
● Collagen, type VI, subunit α3 (COL6A3)

; Chromosome 2q37; Dominant

Nosology: LGMD D5
Gene mutations: >50 identified
- Most mutations located between Exons 3 and 14
- Most are amino acid substitutions: Glycine most common (Gly-X-Y)
  - Usually in triple helix region
  - Some mutations in globular region
  - Disease pathogenesis: ? Dominant negative effect
- Inframe deletion in exon 14 of Collagen α1 (IVS14DS, G-A, +1): Common mutation
- Can also cause disease by stop codon : Produces haploinsufficiency
  - Lower incidence of contractures
- Other disease correlations
  - Most severe disease: COL6A1 multi-exon out-of-frame deletion; Mutations inside triple helix
  - Milder: Exon-skipping mutations; N-terminal globular region
  - Recessive COL6A2 mutations: Stop & Splicing (c.1770delG & R784H in cis) + Missense (R830W)
- Allelic disorders
  - Bethlem myopathy: Dominant
  - Ullrich Scleroatonic muscular dystrophy
    - Same 3 COL6A subunit genes mutated
    - Recessive
  - Myosclerosis: COL6A2 mutations
  - Ossification of posterior longitudinal ligament: Mutations in different part of COL6A1 gene
  - Early-Onset Isolated Dystonia 27 (DYT27) : COL6A3, Recessive
  - Landseer Dogs, Early-onset MD: COL6A1 mutations; Recessive ¹⁰⁰
- Also see: Bethlem myopathy, Collagen XII
Protein: Collagen VI
- Collagen
- Location
  - Extracellular matrix: In most connective tissues
  - Basement membrane
    - Abundant around fat cells, nerves & muscle
    - Normal: Co-localizes with perlecan & collagen IV
    - Mutant: Variable co-localization with perlecan & collagen IV
  - Synthesized by: Interstitial fibroblasts
  - Sources of other collagens
    - Collagens I, III & V: Skeletal muscle
    - Collagen IV & Laminin: Fibroblasts & Mononucleated myoblasts
- Collagen VI synthesis in muscle: By Interstitial fibroblasts
- Monomer: Contains 3 subunits α1 (140kD), α2 (140 kD) & α3 (260kD)
- Subunit domains
  - Short collagenous triple helix of repeating Gly-X-Y sequence
  - Large N- & C-terminal globular regions: Homology to von Willibrand factor type A
- Assembly of monomers: Intracellular
  - First, into antiparallel overlapping dimers
  - Then dimers align in parallel to form tetramers
  - Assembly stabilized by disulfide bridges
  - Forms microfibrillar network
- Possible functions of Collagen VI
  - Anchor basement membranes in extracellular matrix: Interacts with
    - Proteoglycans: Perlican; Decorin; Biglycan; Fibromodulin
    - Other extracellular matrix components: Fibrillar collagens I & II; Fibronectin
  - Bridges cells with the extracellular matrix: Mediated by
    - Integrins: α1β1, α2β1 & α3β1
    - Cell surface proteoglycan: NG2
  - Cell differentiation
  - Apoptosis: Suppression
- Disease mechanisms ¹⁵
  - Glycine mutations: May impair assembly pathway
    - Mildly affected patients (Bethlem): Normal amounts of collagen VI in fibroblast matrix
    - Severely affected patients (Ullrich): Reduced amounts of collagen VI in fibroblast matrix
  - Collagen VI point mutations (G1679E and G1679Q in α3): May produce
    - Lower protein levels
    - Misfolded protein
Clinical features
- Onset
  - Age: Variable within families
    - Prenatal: Fetal movements reduced
    - Neonatal: Hypotonia
    - Early childhood (< 2 years): Common with Weakness or Contractures
    - Adult: As late as 6th decade
  - Motor: Hypotonia
  - Joints: Laxity or Contractures
- Clinical
  - Weakness
    - Diffuse; Proximal > Distal
    - Progressive
      - Usually mild in childhood
      - May become severe & disabling in adulthood
    - Occasional respiratory muscle weakness: Severe cases
    - Falling common in children
    - Face: Spared
  - Muscle cramps or pain: Some patients
  - Muscle size
    - Wasting: Proximal muscles; Distal in legs
    - No muscle hypertrophy
  - Contractures
    - Distribution
      - Flexion: IP joints medial 4 fingers, wrists, elbows, ankles
      - Proximal: Pectorals, Knees, Shoulders, Hips
      - Truncal
        
        Congenital: Torticollis
        
        Disease progression: Restrictive lung disease correlates with weakness & contractures
        
        Spine
      - Dorsiflexion contractures at ankles in COL6A2 (G250S) mutation
    - Course
      - After birth: Often spontaneously improve
      - Joints: Some are initially hypermobile May develop contractures over time
      - Childhood & Adult: May progress independent of weakness
      - Some patients in families may never have contractures
    - No functional impairment
  - Skin
    - Follicular hyperkeratosis (Keratosis pilaris)
    - Keloid formation
    - 'Cigarette paper' scarring over knees
  - Course
    - Early: Benign
    - Improvement in function around puberty
    - Adult
      - Progression in weakness common between 25 & 40 years
      - Many wheelchair-bound in adulthood: Usually 6th or 7th decade
      - Others work into old age
      - Cramps in some patients
  - Cardiac disease
    - Conduction abnormalities described in 10% ³²
  - Differential diagnosis: Emery Dreifuss MD
Laboratory
- CK: Normal or Elevated to 1,750
- EMG: Myopathic; Sparse fibrillatons
- Cardiac: Normal
- MRI: T1W sequences ³¹
  - Vastus lateralis & hamstrings: Peripheral involvement, Central sparing ³⁷
  - Paravertebral involvement
- Muscle ultrasound: "Central cloud"
- Muscle biopsy
  - Non-specific myopathy
    - Fiber size variation
    - Fiber Splitting
    - Internal nuclei
    - Connective tissue increased
  - Lobulated type I muscle fibers
  - Collagen VI
    - Levels: Usually normal; May be reduced
    - Localization: Reduced co-localization with basal lamina (Collagen IV & Perlecan)
  - Laminin β1
    - Reduced in muscle fiber basal lamina but not vessels
    - May also be reduced in Lamin A/C mutations

Bethlem myopathy 2 (BTHLM2)

⁹⁰
● Collagen, type XII, subunit α-1 (COL12A1)

; Chromosome 6q13-q14; Dominant

Epidemiology: 4 families
Genetics
- Mutations: Gly2786Asp; Arg1965Cys; Gly2777Arg
- Allelic with: Ullrich CMD2
- Also see: Bethlem myopathy 1, Collagen 6
COL 12A1 protein
- FACIT collagen
- Interacts with: Collagen I; Decorin; Tenascin X
- Regulates fibrillar scaffolds
- Location: Perimysium
- Mutation: Collagen XII
  - Less abundant
  - Disorganized
  - Intracellular retention
Clinical
- Onset
  - Age: Congenital
  - Hypotonia
  - Distal laxity
- Weakness
  - Motor milestones: Delayed
  - Generalized: Proximal > Distal; Neck
  - Improves: During childhood & teenage years
  - May progress in later decades
- Scapular winging
- Skeletal
  - Joint hypermobility
  - Contractures: Long finger flexors; Proximal
  - Spine: Kyphosis or Scoliosis
  - Facial dysmorphism: Long face, Micrognathia, High-arched palate
- Skin: Atrophic scarring
- Progression: Mild or Improvement
- Heart: Normal
Laboratory
- Serum CK: Normal to 1300
- EMG: Normal or Myopathic
- MRI
  - Common: Rectus femoris atrophy
  - More severe disease: Quadriceps, Adductors & Medial gastrocnemius
  - Asymmetry: Some muscles
- Muscle
  - Collagen: XII reduced in muscle membranes; VI normal
  - Myopathic
  - Endomysial connective tisssue: Increased
  - Laminin B1 reduced
- EM skin fibroblast
  - Col XII retained intracellulary
  - Endoplasmic reticulum: Distorted
Collagen 12A1 variant syndrome: Ullrich congenital muscular dystrophy 2 (UCMD2)
- Epidemiology: 1 family
- Genetics
  - Inheritance: Recessive
  - Mutations: Homozygous; Frameshift
  - Allelic with: Bethlem myopathy 2
  - Also see: Ullrich 1
- Clinical
  - Onset age: Congenital
  - Hypotonia
  - Distal laxity
  - Facial weakness
  - Palate: High arched
  - Skin: Normal in childhood
- Laboratory
  - Muscle & Fibroblasts: Collagen 12 absent

Multiple epiphyseal dysplasia with mild myopathy (EDM3)

¹³
● Collagen, type IX, subunit α-3 (COL9A3)

; Chromosome 20q13.3; Dominant
● Collagen, type IX, subunit α-2 (COL9A2)

; Chromosome 1p34.2; Dominant
● Cartilage oligomeric matrix protein (COMP)

; Chromosome 19p13.1; Dominant

Genetics
- COL9A3
  - Mutation: Splice acceptor mutation in intron 2
  - Mutant collagen IX is poorly cross-linked
  - Allelic with: Intervertebral disk disease, tendency
- COL9A2 mutations
  - Splice donor site of exon 3: c.186G>A; c.186+2T>C
  - Cause skipping of exon 3 from COL9A2 mRNA
  - Allelic with: Intervertebral disk disease, tendency
- COMP mutations
  - C-terminal domain
- Myopathy present with some, but not all, mutations
Type IX collagen proteins
- Collagen
- Fibril-associated collagen with interrupted triple helices
- Chain structure: 4 Noncollagenous domains (NC1-4) separated by 3 triple helical collagenous domains (COL1-3)
- Location (Tissue-specific isoforms): Cartilage; Eye vitreous; Myotendinous junction
- Function: Organization & spacing of type II collagen fibrils
- Modifications: NC3 domain of 2(IX) chain can be modified by a single glycosaminoglycan
COMP protein
- Extracellular matrix protein
- Present at myotendinous junction
- Interacts with cell surface integrin receptors
- Suppresses apoptosis: Blocks activation of caspase-3
- Mutations produce: EDM1
Clinical
- General
  - Onset: Childhood; Knee pain
  - ? Males worse than females
- Weakness: Mild; Symmetric
  - Neck flexion
  - Arms
    - Shoulder abduction
    - Elbow extension
  - Legs
    - Proximal
    - Hamstrings weaker than Quadriceps
    - Waddling gait
- Joints
  - Early onset degenerative disease
  - Especially knees: Pain
  - Sparing: Hips; Distinguishes conditions from Ribbing & Fairbank types of MED
  - Osteoarthritis
    - Joint space narrowing; Femoral condylar bony flattening; Osteophytes & subchondral cysts
    - Onset: Mid-adulthood
- Skeletal: No short stature or brachydactyly
Laboratory
- Serum CK: Mildly elevated
- X-rays: Epiphyses
  - Delayed ossification
  - Small & Irregular
- Muscle biopsy
  - Mild myopathic changes: Varied muscle fiber size
  - Perimysial collagen: Normal
  - Immunostaining: Normal dystrophin, merosin & sarcoglycans
- Epiphyseal chondrocytes: Intracytoplasmic inclusions

Dominant Myopathy with Bone Fragility

⁵¹
● Methylthioadenosine phosphorylase (MTAP)

; Chromosome 9p21.3; Dominant

Nosology: Diaphyseal medullary stenosis with malignant fibrous histiocytoma (DMSMFH)
Clinical
- Weakness
  - Proximal
  - Onset: Mean 29 years
  - Progressive
- Skeletal
  - Fractures, easy
  - Poor healing of long bones
  - Onst: Mean 18 years
- Other
  - Skin: Thin
  - Hair: Premature gray
  - Hernias
Laboratory
- Clotting disorders
- EMG: Myopathic
- Bones: Coarse trabeculation, Patchy sclerosis, Cortical thickening, Narrowing of medullary cavities

Hereditary Inclusion Body Myopathy 4 (HIBM4) ⁸³
● Chromosome 7q22.1-31.1; Dominant

Epidemiology: Chinese Han family, 15 patients
Clinical
- Onset age
  - 4th to 6th decade
  - Earlier in males
- Weakness
  - Early: Proximal legs; Neck flexion; Axial
  - Proximal arms: With disease progression
  - Distal extremities: Occasional; Usually mild
  - ? More severe in males
- Course: Slowly progressive; Walking preserved
Laboratory
- Muscle
  - Necrosis & Regeneration
  - Fiber size: Varied; Some angular fibers
  - Rimmed vacuoles: In atrophic fibers
  - No inflammation
  - Congophilic inclusions: Few
  - Myofibfillar stains: Rare desmin & αB-crystallin aggregates
  - Ultrastructure: Cytoplasmic inclusions, 15�21 nm filaments
- Serum CK: Mildly high; 300 to 400
- EMG: Myopathic; Irritable
- NCV: Normal
- MRI: Medial & Lateral thigh atrophy

Dominant Myopathy with Cardiomyopathy ¹
● Autosomal dominant

Nosology: ? LGMD 1B
Clinical
- Onset: 4 to 38 years
- Weakness
  - Proximal; Symmetric
  - Lower > upper extremity
  - Biceps involved @ 40 years
- Contractures: Mild or absent
- Cardiac
  - Dysrhythmias & conduction disturbances
  - Sudden death
Laboratory
- Serum CK: Median 3x normal; Range - normal to 25x
- EMG & biopsy: Myopathic

Dominant myopathy with Ankle contractures & High CK ¹⁰
● Autosomal Dominant

Clinical
- Male predominance
- Onset: 2nd or 3rd decade
- Weakness: Proximal; Symmetric
- Joint contractures: Ankles
- Progression: Often disabled by 6th decade
- Cardiac: Normal
Laboratory
- Serum CK: Very high; 12x to 55x normal
- Muscle biopsy
  - Variation in muscle fiber size
  - Occasional necrotic muscle fibers

Barnes's Myopathy

Dominant; ? LGMD 1

Other Recessive Myopathies

Familial Limb-Girdle Myasthenia
● Dok-7 (C4ORF25)

; Chromosome 4; Recessive

Myopathy ± Dilated Cardiomyopathy

⁷⁵
● Dolichyl-phosphate mannosyltransferase 3 (DPM3)

; Chromosome 1q22; Recessive

Nosology: Congenital disorder of glycosylation, Type 1o (CDG1O)
Epidemiology: 2 patients
Genetics
- Mutation: Leu85Ser, Leu44Pro; Homozygous
DPM3 protein
- Binds DPM1
- Accessory protein DPM3 of Dol-P-Man synthase
  - Dol-P-Man: Glycosyl donor for all mannosylation reactions on luminal side of ER
Clinical
- Onset
  - Age: 11 to 42 years
  - Weakness: Proximal
  - Waddling gait
- Weakness
  - Proximal
  - Progression: Slow
- Pseudohypertrophy: Gastrocnemius
- Tendon reflexes: Reduced or Normal
- Contractures: Ankle
- Cardiomyopathy in 1 patient
  - Dilated
  - Stroke-like episodes
- Short stature
- CNS & Eye: Normal
Laboratory
- Serum CK: 1500 to 4300
- CDG type I: Defective N-glycosylation in Endoplasmic reticulum
  - Increased ratio of mono- versus diglycosylated transferrin
  - Partial absence of complete biantennary N-glycans
- EMG: Myopathic
- Muscle MRI, Thigh: Hamstring; Adductors; Rectus femoris
- Muscle: Myopathic
  - Fiber-size variation
  - Internal nuclei
  - Necrotic fibers
  - Rimmed vacuoles
  - Fiber splitting
  - Endomysial fibrosis
  - α-Dystroglycan: Reduced

LGMD 2W: Myopathy with Cardiomyopathy & Triangular Tongue

⁹¹
● Lim and senescent cell antigen-like domains 2 (LIMS2; PINCH2)

; Chromosome 2q14.3; Recessive

Epidemiology: 1 Canadian family
Genetics
- Mutations: Missense; L345P, P119L, N114K
LIMS2 protein
- Z-disk
- Functions: Adhesion; Integrin signalling
Clinical
- Onset age: Childhood
- Weakness
  - Severe
  - Arms & Legs
  - Face spared
- Tongue
  - Triangular
  - Macroglossia
- Muscle size: General atrophy; Calf hypertrophy
- Cardiomyopathy: LV dysfunction; Onset in 3rd decade
Laboratory
- Serum CK: Very high; Up to 5,000
- MRI: Muscle atrophy
- Muscle
  - Fiber size: Varied
  - Internal nucle
  - Endomysial connective tissue: Increased
  - PINCH2 staining: May be reduced

LGMD 2X: Myopathy with Arrhythmias

¹⁰³
● Popeye domain�containing 1 gene (POPDC1; BVES)

; Chromosome 6q21; Recessive

Epidemiology: 2 families, 6 patients
Genetics
- Mutations
  - Missense: c.602C>T, p.Ser201Phe; Homozygous; Pseudo-dominant
  - Splice site: intron 8 (c.816 + 2T>C).
POPDC1 protein
- Localization: Plasma membrane; T-tubule; Nuclear envelope
- cAMP-binding & effector protein
- Expressed in cardiac & skeletal muscle
- Cell adhesion molecule
- Formation & regulation of tight junction paracellular permeability barrier in epithelial cells
- VAMP3-mediated vesicular transport
- Interactions: Caveolin-3; TREK-1
- Nosology: Blood vessel epicardial substance (BVES)
Clinical
- Onset age: 3rd to 5th decade
- Weakness: Proximal legs; Symmetric
- Cardiac: Syncope; A-V block
Laboratory
- Serum CK: 700 to 8000
- EMG: Myopathic
- Muscle biopsy
  - Fiber size: Varied
  - Internal nuclei
  - Necrosis & Regeneration: Scattered

Myopathy with Contractures (LGMD 2Y)

● Torsin A-interacting protein 1 (TOR1AIP1; LAP1B)

; Chromosome 1q25.2; Recessive

Epidemiology: 1 Turkish family, 3 patients
Genetics
- Mutation: Frameshift; Homozygous c.186delG
LAP1B protein
- Location: Inner nuclear membrane
- Binds type A & B lamins
- ? Regulates TorsinA ATPase
Clinical
- Onset age: 1st decade
- Contractures
  - Rigid spine
  - Interphalangeal joints: Distal & Proximal
- Weakness: Limb-Girdle
- Cardiomyopathy, dilated: 1 patient
Laboratory
- Serum CK: 80 to 500
- Muscle
  - Muscle fibers: Varied size; Internal nuclei; Mild necrosis
  - Endomysial connective tissue: Increased
  - TOR1AIP1: Absent
  - Ultrastructure: Abnormal nuclear envelope

Myopathy with Satellite cell loss (LGMD R21)

¹⁰⁵
● Protein O-glucosyltransferase 1 (POGLUT1)

; Chromosome 3q13.33; Recessive

Nosology: LGMD 2Z
Epidemiology: Spanish family, 4 siblings
Genetics
- Mutation: Homozygous; Missense; D233E
- Allelic disorder: Galli-Galli/Dowling-Degos disease (DDD4)
POGLUT1 protein
- Notch posttranslational modification
  - Notch pathway: Maintains Satellite cell quiescence
- O-Glucosyltransferase activity on Notch
- Specifically adds O-glucose or O-xylose to properly folded EGF repeats containing CXSX(P/A)C consensus sequence
- Glycosyltransferase: Directly add sugar molecules to an amino acid & not to other sugars
- Mutation: Impairs muscle development
Clinical
- Onset age: 3rd decade
- Weakness
  - Proximal
  - Legs > Arms
  - Scapular winging
  - Respiratory: 4th decade
- Course: Slow progression; Some rrequire wheelchair
Laboratory
- Brain MRI: Normal
- Muscle MRI: Internal thigh muscle pathology
- Muscle
  - Fiber size: Varied
  - Endomysial connective tissue: Increased
  - Nuclei: Internal in some muscle fibers
  - α-Dystroglycan: Hypoglycosylation
  - Satellite cells: Reduced numbers
- Serum CK: Normal or Mildly high

Cardiomyopathy + Myopathy ¹¹⁵
● Tripartite motif-containing protein 63 (TRIM63; Murf1)

; Chromosome 1p36.11; Recessive

Epidemiology: 2 paatients
Genetics
- Mutation: p.Q247X, Homozygous
- Variant: Digenic syndrome
Trim63 protein
- Regulator of muscle atrophy
- Expression: Skeletal & Cardiac muscle
Clinical
- Onset age: 6th decade
- Strength: Normal
Laboratory
- Cardiac hypertrophy
- Serum CK: 700
- EMG: Myopathy, Mild
- Muscle MRI
  - Patchy asymmetric changes
  - Muacles involved: Gluteus minimus� Vastus lateralis, Semimembranosus, Medial gastrocnemius
- Muscle biopsy
  - Necrotic fibers: Few
  - Muscle fiber size: Varied
  - Internal nuclei
  - Internal capillaries: 5�10% of muscle fibers
TRIM63 variant syndrome: Cardiac & Skeletal Aggregate Myopathy with Combined MuRF1 & MuRF3 mutations ¹¹⁶
- Epidemiology: 1 patient
- Genetics: Digenic
  - Murf1 (TRIM63) mutations: p.Q247X, Homozygous
  - Murf3 (TRIM54) mutation: p.Asp106Asn, Heterozygous
- Clinical
  - Onset age: 15 years
  - Weakness
    - Distribution: Arms & Legs; Proximal; Symmetric
    - Gait: Waddling
    - Respiratory: Moderate reduction
    - Course: Slow progression
  - Muscle hypertrophy: Deltoids, Biceps, Calf
  - Scapular winging
  - Rigid spine, hypertrophy
- Laboratory
  - Echocardiogram: Hypertrophic cardiomyopathy
  - EKG: Atrial flutter & enlargement
  - Serum CK: 2x to 6x high
  - EMG: Myopathic
  - Muscle MRI
    - Subcutaneous tissue: Reduced
    - Fat replacement: Lumbar paraspinous; Glutei; Thigh, anterior & posterior
    - Hypertrophy: Rectus femoris, Sartorius, Gracilis
  - Muscle biopsy
    - Fiber sizes: Some small fibers
    - Fiber aggregates
      - Location: Sub-sarcolemmal
      - Type I fibers
      - Components: MyHC, MuRF3, M-protein, Myomesin
      - Ultrastructure: Aberrantly oriented sarcomere fragments
    - Nuclei: Large
    - Endomysial connective tissue: Mildly increased

Congenital disorder of glycosylation, Type Iu (CDG1U; DPM2-CDG): Myopathy with Epilepsy & Microcephaly

● Dolichyl-phosphate mannosyltransferase 2 (DPM2)

; Chromosome 9q34.13; Recessive

Epidemiology: 2 Sicilian families
Genetics
- Mutations: c.4-1G>C (Disrupts acceptor splice site of exon 2; Y23C
DPM2 protein
- Dolichol-phosphate-mannose (Dol-P-Man; DPM) synthase complex component
- Catalyzes synthesis of DPM at cytosolic face of ER membrane
Clinical
- Onset age: Congenital
- Microcephaly, progressive
- Visual defect, Severe
- Epilepsy
- Muscular dystrophy: Hypotonia
- Liver involvement
- Death: < 18 months
Laboratory
- Coagulation factors: Decreased
- Serum CK: High; 1,200 to 1,400
- EMG: Myopathic
- Muscle
  - Fiber-size variation
  - Internal nuclei
  - Endomysial fibrosis
  - Reduced: α-Dystroglycan; Laminin-α2
- Transferrin: Abnormal N-glycosylation
- Brain MRI: Cerebellar vermis hypoplasia

Myopathy with Lipodystrophy (Congenital generalized lipodystrophy, Type 4; CGL4)

⁷⁶
● Polymerase I and transcript release factor (PTRF; Cavin-1; FKSG13)

; Chromosome 17q21.31; Recessive

Epidemiology
- 5 unrelated Japanese families
- Omani & UK families
Genetics: Mutations
- Homozygous or Heterozygous
- c.525delG, c.696_697insC, c.160delG, c.362dupT
PTRF protein
- Termination of RNA polymerase I (Pol I)
- Release of both pre-rRNA & Pol I from template
- Required for caveola formation & sequestration of mobile caveolin into immobile caveolae
Clinical
- Onset
  - Age: Infancy or early childhood
  - Lipodystrophy
- Lipodystrophy
  - Generalized
  - Loss of adipose tissue in several regions including face
- Weakness
  - Mild
  - Distal dominant or Generalized
- Muscle
  - Muscle hypertrophy
  - Muscle activity
    - Muscle mounding
    - Rippling
    - Electrically silent
  - Myalgias: Occasional
- Cardiac
  - Tachycardias: Supraventricular & Ventricular
  - Bradycardia
  - Long-QT syndrome
  - Sudden cardiac death: Teens
- GI
  - Smooth muscle hypertrophy
  - Hypertrophic pyloric stenosis
  - Impaired gastrointestinal motility: Constipation
  - Chalasia
- Bone
  - Impaired bone formation
  - Osteopenia
  - Osteoporosis
  - Atlanto-axial instability
  - Skeletal: Lordosis or Scoliosis
- Other systems
  - Acromegaloid features
  - Umbilical prominence
- Immune: Some patients
  - Transient immunodeficiency (IgA)
  - Recurrent pneumonia
- Not present
  - Intellectual deficit
  - Acanthosis nigricans
Laboratory
- Serum CK: High; 500 to 2600
- Muscle
  - Chronic dystrophic changes
    - Variation in fiber size: Marked
    - Enlarged fibers
    - Internal nuclei
    - Endomysial fibrosis
    - Necrotic & Regenerating fibers: Few
  - Caveolin family members
    - Deficiency & Mislocalization of all 3
    - Caveolin-3: Reduced on sarcolemma: Increased in cytoplasm
    - Caveolin-1 & Caveolin-2: Reduced in blood vessels
    - Caveolae structure: Reduced
  - Dysferlin: Decreased in sarcolemma; Mislocalized into cytoplasm
  - PTRF: Absent from muscle by Western blot
  - Normal: Dystrophin, Sarcoglycans, Dystroglycans, Emerin, Merosin, Collagen VI

Ehlers-Danlos with Myopathy

⁸⁸
● Tenascin-XB (TNXB)

; Chromosome 6p21.33; Recessive

Epidemiology: 2 patients
Genetics
- Mutations
  - 30 kb deletion: Leads to fusion gene with pseudogene TNXA; Truncating
  - Arg4072Cys
- Allelic with: Ehlers-Danlos syndrome, autosomal dominant, hypermobility type
TNXB protein
- Extracellular matrix of muscle & Blood vessels
- Regulator of collagen deposition by dermal fibroblasts
Clinical
- Weakness
  - Onset age: 4th decade
  - Proximal & Axial
  - Symmetric
  - Weakest muscles: Abdominal; Knee extensors
  - Scapular winging
  - Functional: Difficulty running
  - Muscle bulk: Reduced
  - Course: Slowly progressive
- Tendon reflexes: Reduced
- Skin: Hyperextensible
- Hematomas: After minimal trauma
- Contractures: Fingers or None
Laboratory
- EMG: Myopathic; Pseudomyotonic discharge
- NCV: Normal
- Serum CK: High; Up to 5x normal
- CT: Rectus femoris most preserved in Thigh; Distal legs normal
- Cardiac echo: Systolic function mildly reduced
- Platelet aggregation: Mildly abnormal
- Muscle
  - Soft consistency
  - Fiber size: Varied
  - Internal nuclei
  - Fiber type groupisng
  - Myotendinous junctions: Increased
  - Endomysial connective tissue: Normal
  - Tenascin-X staining: Reduced in muscle & skin
  - Ultrastructure: Plasma membrane focally disrupted; Basal lamina abnormally folded

LGMD 4

● Autosomal Recessive

Northern Indiana Amish
Linked to LGMD 2E

Metabolic myopathies

Lipid Storage
- Carnitine Deficiency
- Riboflavin Responsive (multiple enzyme deficiencies)
Acid Maltase deficiency & other Glycogen storage syndromes

Infantile autophagic vacuolar myopathy ⁵⁶
● Autosomal Recessive

Epidemiology: 2 Japanese patients
Onset: Congenital Hyoptonia
Clinical
- Progression: Developmental delay
- Cardiomyopathy: Cardiomegaly
- Death: 2 to 30 months
Muscle: Vacuoles, autophagic
- LAMP-2 staining
- Contain glycogen granules

Childhood autophagic vacuolar myopathy ⁵⁷
● Autosomal Recessive or X-linked carrier

Epidemiology: 1 family; 2 British females
Onset: 12 years
Clinical
- Early developpment: Normal
- Weakness
  - Legs > Arms
  - Proximal > Distal
  - Neck flexor
- Contractures: Knee
Laboratory
- Serum CK: High, 500 to 700
- EMG: Myopathic
- MRI: Wasting of thigh muscles sparing adductors
- Muscle
  - Autophagic vacuoles
  - Endomysial connective tissue: Mildly increased

Adult-onset autophagic vacuolar myopathy with multiorgan involvement ⁵⁸
● Sporadic

Epidemiology: 1 Japanese male
Onset: Myopathy as adult
Clinical
- Ocular
  - Achromatopsia: From childhood
  - Retinal pigmentary degeneration: Blindness in 3rd decade
  - Optic atrophy
- Weakness
  - Proximal > Distal
  - Scapular winging
- Other muscle
  - Exertional pain
  - Dyspnea
- Cardiomyopathy
  - EKG: Bradycardia with transient sinus arrest & prolonged PQ interval
  - Echocardiography: Hypertrophy & partial dilatation of left ventricular wall; Decreased ejection fraction
- Lung: Fibrosis
Laboratory
- Serum CK: High, 500
- IgG & IgE: High
- ⁶⁷Ga uptake in skeletal muscles
- Muscle
  - Autophagic vacuoles
  - Fiber size: Moderate variation
- Liver: Vacuoles in hepatocytes
- Renal: Proteinuria

Cardiomyopathy, Retinal degeneration & Epilepsy ⁹³
● CLN3

; Chromosome 16p11.2; Recessive

Epidemiology: 4 families, 5 patients
Genetics
- Mutations: Missense (Gly165Glu), Splice & Stop; Common 1 kb deletion
- Allelic disorder: Neuronal ceroid lipofuscinosis, juvenile form
CLN3 protein
- Organs: Brain + other tissues
- Subcellular: Nucleus & Cytoplasm; Lysosomal
- Cellular: Astrocytes & Endothelium
Clinical
- Onset age: 6 to 9 years
- Eye
  - Early in disease course
  - Retinitis pigmentosa
  - Visual loss
- CNS
  - Epilepsy: Tonic-clonic
  - Cognitive: Mild impairment of verbal fluency & executive functions
- Cardiac
  - Hypertrophic cardiomyopathy
  - Sick sinus syndrome
  - Conduction defect
  - Onset: Later in disease course
- Motor function: Normal
- Course: Slow progression over decades
Laboratory
- Serum CK: Up to 600
- Muscle
  - AVSFs
  - Autophagic debris: Acid phosphatase +
  - Autofluorescent material
- EMG: Myopathy, mild
- EEG: Spikes & sharp waves
- Blood lymphocytes: Cytoplasmic vacuolization
- Brain MRI: Cerebral & Cerebellar atrophy

X-linked myopathies

Becker muscular dystrophy
● Dystrophin partial deficiency; Chromosome Xp21; Recessive
Emery-Dreifuss: Contractures & Cardiac
● Emerin; Chromosome Xq28; Recessive
McLeod Syndrome: Acanthocytosis & Chorea
Barth syndrome
X-linked myopathy with excessive autophagy

X-linked Myopathy with Excessive Autophagy (MEAX; XMEA)

^5, ¹⁶
● VMA21 vacuolar H+-ATPase homolog (VMA21; ATP6V0E1; LOC203547)

; Chromosome Xq28; Recessive

Epidemiology: Families in Europe & North America, ~14
Genetics
- VMA21 mutations ⁷¹
  - Single nucleotide substitutions
  - Locations: Intron; Splice site; 3' UTR
  - Mutation effects: Reduced VMA21 abundance
  - c.164-7T>G: Childhood & adult onset patients
  - Non-coding microdeletions (c.54-16_54-8del; c.*13_*104del): More severe, early-onset disease
- Allelic with: Congenital Autophagic Vacuolar Myopathy (CAVM): c.16426t>g mutation
VMA21 protein (Vacuolar H⁺-ATPase homolog)
- Assembly chaperone for: V-ATPase
  - Principal mammalian proton pump complex
  - May pump 2-3 H⁺ per ATP hydrolyzed
  - Acidify vesicles: Golgi-derived, Clathrin-coated, Synaptic
  - Inhibitor: Bafilomycin
- Decreased VMA21
  - Raises Lysosomal pH: Increased from 4.7 to 5.2
  - Lysosomal degradative ability: Reduced
  - Autophagy: Blocked
  - Cellular free amino acids: Reduced
  - mTOR pathway & mTOR-dependent macroautophagy: Down regulated
  - Proliferation of large & ineffective autolysosomes
    - Engulf sections of cytoplasm, merge & form vacuoles
- Disease mechanism
  - Macroautophagic overcompensation: Leads to cell vacuolation & tissue atrophy
Clinical: Similar patterns among families
- Onset
  - Age: Range Neonatal to 50 years; Typical 5 to 10 years
  - Weakness: Difficulty climbing stairs & running
  - Neonatal onset: Hypotonia; Rapid progression
- Weakness
  - Common: Limb-Girdle; Mild
    - Proximal
    - Symmetric
    - Legs > Arms
  - Distal: Ankles
  - Eyes: Up & Lateral movements limited in more severe patients
- No muscle hypertrophy or clinical myotonia
- Progression
  - Common: Very slow or Stable
  - Longevity: Not altered
  - Many patients in wheelchair by 6th decade
- Cardiac: Normal
- CNS
  - Intellect: Normal
  - Seizures: More severe patients
- Female carriers: Normal or Mildly affected
Laboratory
- Serum CK: 2x to 15x elevated; Higher in adolescence than childhood
- EMG
  - Myopathic
  - Motor units: High amplitude; Polyphasic; Normal duration
  - Spontaneous activity
    - Myotonic & High frequency discharges
    - May occur in clinically unaffected muscles
  - Most affected muscles: Psoas; Anterior thigh; Posterior leg
Muscle biopsy
- Muscle fibers
  - Variable fiber size
  - Necrosis: Little or None
  - Vacuoles: Autophagic with sarcolemmal features (AVSF)
    - Excessive autophagic activity
    - Location: Sarcoplasm; Internal or Near surface
    - Size: 2 to 10 μm
    - Basophilic granules
    - Contents
      - Lysosomal enzymes (Hydrolases)
      - Calcium
      - C_5b-9 complement components
      - Cellular debris
      - Acid phosphatase: Variably present
    - Immunostaining
      - Dystrophin: Vacuolar membrane staining
      - LAMP-2 & Sarcoglycans
      - Caveolin-3
      - α1-Antitrypsin: Within vacuoles
    - Vacuolated fibers express polysialylated isoform of NCAM
    - Unable to complete digestion of contents
      - Migrate to myofiber surface
      - Fuse with sarcolemma
      - Exocytosis of phagocytosed material: To extracellular space
    - Differential diagnosis
- Basal lamina
  - Affected fibers surrounded by multiple layers
  - Contains Granular material
- Complement deposits
  - Sarcolemma & vacuoles
  - Granular pattern

X-linked Vacuolar Cardiomyopathy and Myopathy (Danon's disease)

● Lysosome-associated membrane protein 2 (LAMP-2)

; Chromosome Xq24; Dominant, more severe in males

Genetics
- Mutations
  - Frameshift; Nonsense; Insertion
  - Cause protein truncation
  - Usually cause absent LAMP-2 in muscle: 1 family with some residual LAMP-2
  - May affect
    - LAMP-2B only: No mental retardation in males; Milder or no signs in females
    - Both LAMP-2 isoforms: Most common pattern; Typical disease manifestations
- Allelic disorder: Scapuloperoneal muscular dystrophy with mental retardation & lethal cardiomyopathy
LAMP-2 protein
- Type 1 membrane protein: 3 domains; Luminal, Transmembrane, Cytoplasmic
- Lysosomal: Coats inner side of membrane
- Highly glycosylated
- 3 Isoforms: Lysosomal
  - LAMP-2A: Ubiquitous
    - Chaperone-mediated autophagy
    - Oxidized proteins
    - Increased during starvation
  - LAMP-2B
    - Cardiac & Skeletal muscle
    - Macroautophagy
  - LAMP-2C: ?
- LAMP-2 deficiency: Affects
  - Chaperone-mediated autophagy
  - Lysosomal biogenesis
  - Lysosome-autophagosome fusion
  - Lysosomal movement along microtubules
Clinical ²⁹
- Onset
  - Age: Infantile to 2nd decade; Childhood most common; Mean onset 13 years
  - Cardiac
- Weakness
  - Often mild: All patients remain ambulatory
  - Distribution: Symmetric; Shoulder girdle & Neck; Proximal ± Distal
  - Frequency: Most patients; 85%
  - Fatigability without fixed weakness: 10%
  - Wasting: 15%
  - Monophasic severe post-operative weakness: 1 patient ⁸⁴
- Cardiomyopathy (Nearly 100%) ⁷²
  - Symptoms: Chest pain, Palpitations, Syncope, Cardiac arrest.
  - Hypertrophic: Concentric; Impaired LV function; Thick IV septum & posterior walls
  - Left ventricular systolic dysfunction, ejection fraction ~25%
  - Left ventricular cavity enlargement
  - Treatment: Pacemaker or Heart transplantation
  - EKG
    - Abnormal in 100%: Arrhythmia
    - Ventricular preexcitation
    - Wolff-Parkinson-White; Short PR intervals; High precordial voltage
  - Echocardiography: Concentric left ventricular hypertrophy
  - Prognosis: Poor
    - Progression to end stage heart failure in early adulthood
    - Sudden death
- Mental retardation: 80%; Mild or absent in 40%
- Hepatomegaly: 35%
- Foot deformities: 38% of males
- Retinopathy
  - Loss of pigment in retinal pigment epithelium
  - Reduced visual acuity: Mild
- Course
  - Some with death in 2nd to 5th decade
  - Cause of death: Cardiac failure
Laboratory
- Serum CK
  - High in most (4x to 35x normal; 300 to 3,000)
  - May be normal (10% to 20%)
  - Patients may present with asymptomatic high CK
- EMG: Myopathic (100%); Myotonia (30%); Spontaneous activity (30%)
- Nerve conduction tests: Normal
- EEG: Mild abnormalities in 28%
- Liver enzymes: High
- CNS: Normal brain MRI
Muscle pathology
- Vacuoles: Similar to XMEA
  - Autophagic: Contain lysosomal enzymes
  - Cytoplasmic: Small solid basophilic granules
  - Histochemistry: Acid phosphatase, Nonspecific-esterase & Acetylcholinesterase staining
  - Immunocytochemistry: Stain for Dystrophin; Laminin; limp-1
  - Ultrastructure: Vacuoles contain glycogen particles & cytoplasmic debris
  - Present in males & females
- Myopathy: Variation in muscle fiber size
- Glycogen: Increased or Normal amount; Free & membrane bound
- Lamp-2 protein staining: Absent with most mutations; Rarely residual LAMP-2A isoform
- Heart: Fibrosis; Intracytoplasmic vacuoles
Danon syndrome: Variant with early weakness but no retardation ⁵⁵
- Mutation: Gly384Arg
- Onset
  - Age: Childhood to 4th or 5th decade
  - Leg weakness
- Clinical
  - Weakness
    - Legs: Distal > Proximal
    - Arms
    - Face
    - Sleep apnea
  - Gynecomastia
  - Cardiac: Some patients
    - Sick sinus syndrome
    - Atrial fibrillation
  - No mental retardation
  - Female carriers
    - Cardiac disease: Arrhythmias
    - One with weakness
- Pathology: Muscle
  - Autophagic vacuoles
  - Glycogen: Increased
  - LAMP-2: Normal staining
Variant: Carrier females
- Frequency
  - > 70% of carriers
  - All eventually have abnormal EKG
- Clinical
  - Onset
    - Age: 12 to 53 years
    - Cardiac signs
  - Weakness: 33%; Proximal limb & Neck
  - Cardiomyopathy
    - Dilated > Hypertrophic
    - Arrhythmia: Pacemaker in 17%
  - Retinopathy
    - Pigmentary changes: Peripheral
    - Electroretinogram: Abnormal
    - Visual fields: May be abnormal central region
  - Course: Some with death in 4th & 5th decade
- Laboratory
  - Serum CK: 76 to 643
  - Muscle biopsy
    - Vacuoles
    - LAMP-2 staining: Absent or Reduced
- Treatment: Cardiac transplantation or Pacemaker
Danon syndrome: Variant
- Scapuloperoneal muscular dystrophy with mental retardation & lethal cardiomyopathy

Myofibrillar (Desmin -storage) Myopathies ³^,¹¹

MFM: Hereditary types
Congenital
Cap
TPM2: 9p13
TPM3: 1q22
ACTA1: 1q42
MD: SEPN1; 1p36
MD + JEB: Plectin; 8q24
Myopathy: CCDC78; 16p13
Childhood
MFM
1 (LGMD 1E): Desmin; 2q35
2: αB-crystallin; 11q22
3 (LGMD 1A): Myotilin; 5q31
4: ZASP; 10q23
5: Filamin C; 7q32
6: BAG3; 10q25
7: KY; 3q22
8: PYROXD1; 12p12
MFM: ACTA1; 1q42
Myopathy & Respiratory Δ
Type 1: Titin; 2q31
Type 2: 2q21
Other
Distal myopathy: HSPB8; 12q24
DMRV: SQSTM1 + TIA1
LGMD
1B; LMNA; 1q21
1D: DNAJB6; 7q36
2Q: Plectin; 8q24
Polyglugosan body: RBCK1; 20p13
Restrictive cardiomyopathy
Scapuloperoneal: FHL-1; Xq26

MFM
Clinical features
Pathological features

Also see
Contractures + Weakness: KY; 3q22
Desmin knock-out mouse
Inclusion body myositis
Intermediate filament disorders

Desmin aggregates

Myofibrillar myopathies: General ¹¹⁴

Clinical features
- Weakness
  - Proximal & Distal
  - May present with respiratory failure
- Cardiomyopathy (50%)
- EMG
  - Myopathy
  - Irritability: Fibrillations; Positive sharp waves
  - Myotonia
  - Complex repetitive discharges
- Serum CK: Normal, or Elevated < 5x
Pathological features
- Initial: Centered on Z-disc
- Degradation (focal) primarily affecting myofibrils
  - Lytic lesions depleted of actin, α-actinin ± titin, nebulin, or myosin
  - Inappropriate expression of
    - Cell division cycle (CDC) 2 kinase
    - Cyclin-dependent kinases (CDK) 2, 4 & 7
- Hyaline spheroid & granular structures: Staining patterns
  - Gomori trichrome: Amorphous, hyaline, or granular material
  - Contain compacted & degraded myofibrillar structures
  - NADH: Circumscribed reduced staining
  - React intensely for actin
  - Congo red positive
- Numerous proteins accumulate in lesions & muscle fibers
  - Desmin, lamin-B, gelsolin, ubiquitin, α₁-antichymotrypsin, NCAM, N-terminal β-AP, myotilin (90%)
  - Ectopic dystrophin & γ-sarcoglycan
  - Ectopic expression of lamin B & nuclear matrix protein in cytoplasm
  - Amyloid deposits

Myofibrillar myopathies: Specific syndromes

Myofibrillar myopathy 1 (MFM1)
● Desmin

; Chromosome 2q35; Dominant or Recessive

Nosology
- Myofibrillar myopathy with desmin mutations
- One family originally identified as: HIBM1
Gene mutations
- Location
  - Most mutations: Carboxy-terminal of rod domain (Helixes 1B & 2B)
  - Occasional mutations in head or tail domains
- Types
  - Usually: Missense
  - Occasional: Splice site with exon skipping; In-frame deletion; Small insertion
- Recessive mutations: 6%; Mean onset = 5 years
- Mutation Database: HGMD
- Allelic with
  - Dominant
    - Myopathies
    - Cardiomyopathies
      - Dilated: 1F, 1I
      - ARVD7
  - Recessive
Desmin protein features ⁴³

From C Weihl MD
- Vimentin-like intermediate filament
  - Appearance follows vimentin in development
  - 53 kDa monomer
  - Domains: Head; Rod; Tail
  - Assembles into 10nM diameter filaments
  - Non-polar filament
- Location
  - Cytoplasm: Subsarcolemmal; Z-band encircled
- Tissues: Muscle specific
  - Skeletal
    - 0.35% of total cell protein
    - Major intermediate filament in muscle
    - Increased amounts at: Myotendinous & Neuromuscular junctions
    - Development
      - Low in replicating myoblasts & satellite cells
      - High in differentiated myotubes
    - Mutations
      - Levels of mutant protein: Vary within regions of single fibers
  - Cardiac: 2% of total cell protein
  - Smooth: Especially resistance-sized mesenteric microarteries
- Functions
  - Overall: Links myofibrils to sarcolemma, nucleus & mitochondria
  - Contractile apparatus in muscle
    - Role in maintenance of structural & mechanical integrity
    - Force transmission
  - Mitochondrial function
    - Influences: Position, Movement & Respiratory activity
- Desmin interactions: Binding to
  - Ankyrin
  - Spectrin
  - Synemin : Interacts with α-dystrobrevin, vinculin & α-actinin
  - Desmuslin
  - Syncoilin
  - Plectin: Links cytoskeleton & intermediate filaments
  - Nebulin: C-terminus
- Inclusions
  - Cytoplasmic, Spheroid, Mallory, Lewy bodies
  - Associated with: Actin; Ubiquitin; Heat shock proteins (α-B crystallin); Amyloid proteins
- Mutant desmin
  - Abnormal assembly of intermediate filaments
  - Produces fragility of myofibrils
Myopathy + Cardiomyopathy (MFM1)
- Genetics
  - Inheritance: Dominant
  - Mutations: Heterozygous; Ala337Pro; Leu345Pro; L370P
  - Mechanism: ? Dominant negative effect on filament formation
- Clinical
  - General
    - Syndromes may involve skeletal muscle, heart or both
    - Smooth muscle involved in some syndromes
    - Inter- and intra-familial variability with same mutation
  - Skeletal myopathy
    - Onset: 20's & 30's
    - Early: Distal progressing to Proximal weakness
    - Patterns of weakness
      - Scapuloperoneal
      - Limb-Girdle
      - Distal
      - Distal + Proximal
      - Also see: R350P (Kaeser scapuloperoneal syndrome)
    - Progression of weakness
      - Limbs; Neck; Pectoral; Bulbar & Facial
      - Disability: Wheelchair, walker or braces in 75%
      - Respiratory failure in some families
  - Cardiac involvement (60%)
    - EKG: Right bundle branch block; ST segment elevation
    - Syncopal episodes: Pacemaker often required (40%)
- Laboratory
  - Serum CK: Mildly elevated in 50%
  - EMG: Myopathic; Fibrillations
  - Muscle pathology
    - Variable fiber size
    - Internal nuclei: Increased
    - Storage: Desmin, Vimentin & Nestin accumulate in muscle fibers
      - Location
        
        Cytoplasmic
        
        Subsarcolemmal & some sarcoplasmic aggregates
      - Accumulations also contain dystrophin
      - Aggregates may have different shapes in type 1 & 2 muscle fibers
      - Ultrastructure: Granulofilamentous material
    - Occasional: Rimmed vacuoles; Small rods
Desmin variant syndrome: Distal myopathy, Cardiomyopathy & Sarcolemmal Vacuoles ⁹⁸
- Epidemiology: 2 families
- Genetics
  - Inheritance: Dominant
  - Mutations: R454W (Tail domain); I402N
- Clinical
  - Onset age: 3rd to 5th decades
  - Myopathy
    - Weakness
      - Distal > Proximal
      - Respiratory
      - Symmetric
    - Atrophy: Distal
  - Cardiac
    - Conduction block
    - Cardiomyopathy: Dilated
- Laboratory
  - Serum CK: Mildly high; 280 to 810
  - EMG: Myopathic; Fibrillations, distal
  - NCV: Normal
  - Muscle
    - Fiber size: Varied; Clustered atrophy
    - Internal nuclei
    - Ensomysial connective tissue: Increased
    - Aggregates: Desmin
    - Cytoplasmic bodies
    - Vacuoles: Autophagic with Sarcoplasmic features (AVSF)
Desmin variant syndrome: LGMD 2R
- Genetics
  - Inheritance: Recessive
  - Mutations: Compound heterozygosity (Type 3); Ala360Pro & Asn393Ile
  - Heterozygote carriers: Not involved
- Clinical
  - Cardiac
    - A-V conduction block: Require pacemaker at ages 2 to 10
    - Cardiomyopathy onset: Childhood to 20's
  - Weakness
    - Proximal & Facial
    - Onset 20's
    - Respiratory involvement
  - Skeletal
    - High arched palate
    - Scoliosis
  - Pathology
    - Hyaline/desmin plaques (Mallory body-like)
    - Amorphous subsarcolemmal material
      - Desmin- & dystrophin-immunoreactive
Desmin variant syndrome: Scapular myopathy, Early onset ⁷³
- Genetics
  - Homozygous in-frame deletion
  - Mutation: p.R173_E179del
- Desmin: Mutated protein
  - No assembly of desmin filaments
  - Reduced ability to form intermediate filament network
- Clinical
  - Onset
    - Age: 6 months
    - Syncope
  - Cardiomyopathy
  - Weakness: Progressive
    - Face & Ptosis
    - Proximal & Distal
    - Scapular winging
  - Tendon reflexes: Reduced
  - Death: 20 years
- Laboratory
  - EMG: Complex repetitive discharges; Myotonic discharges; Fibrillations
  - EKG: Ventricular tachycardia, QT interval prolonged; 2nd degree AV block
  - Muscle: Desmin aggregates, subsarcolemmal (Cap-like); Small vacuoles
Desmin variant syndrome: Myopathy, Adult onset ⁸⁷
- Epidemiology: Turkish family
- Genetics
  - Inheritance: Recessive
  - Mutation: c.1289-2A>G (Tail domain; Lamin B interaction)
  - Homozygous splice site mutation
- Clinical
  - Onset age: 2nd or 3rd decade
  - Weakness
    - Distribution: Proximal; Symmetric; Face, mild
    - May be severe
    - Scapular winging
    - Course: Wheelchair in 2 decades
  - Contractures: Elbow
- Laboratory
  - Muscle pathology
    - Fiber size: Varied
    - Necrosis: Occasional
    - Endomysial connective tissue: Increased
    - Type 2 predominance
    - Desmin staining: Present; No aggregates
  - Serum CK: Normal
  - EKG: Right bundle branch block
  - Cardiac echo: Normal
Desmin variant syndromes: Cardiomyopathies
- Types
  - Familial hypertrophic
    - Desmin point mutation; Dominant
  - Dilated Cardiomyopathy 1I
  - Restrictive
- Other features
  - Atrioventricular conduction abnormalities: Require pacemaker
  - Sudden death
  - Heart disease eventually in > 60% of desminopathies
  - Earlier onset in cases without skeletal myopathy

Myofibrillar myopathy 2 (MFM2)

(Type 1) ³⁹
● αB-crystallin (CRYAB; HSPB5)

; Chromosome 11q23.1; Dominant or Recessive

Genetic: Autosomal dominant
- Mutations: Myopathy
  - Missense: Arg120Gly
  - Truncating: C-terminal; 464delCT & Gln151X
- Other mutations in same gene
  - Dominant Congenital Posterior Polar Cataract: 1-BP Del, 450A
  - Fatal infantile hypertonic myofibrillar myopathy, Recessive
  - CMD 1II: Cardiomyopathy, Familial dilated
CRYAB protein

From HPRD
αB-crystallin
- Type: Heat shock protein 20 (HSP20) family
- Location
  - Tissues: Muscle; Lens; Myocardium; Kidney epithelium
  - Subcellular: Cytosol
- Functions
  - Chaperone: Desmin& Actin
  - Lens: Forms aggregates with αA-crystallin; Maintains lens transparency
  - Cytoprotective: Target of p53
- Major component of Rosenthal fibers in Alexander's disease
- Mutant protein
  - Expressed
    - Even with truncation mutations
    - Lower levels than normal protein
  - Forms complexes with wild type protein
  - Probably exerts dominant negative effect
- External link: HPRD
Clinical: Variable
- General
  - Some families with only single system involved: Cataracts, Myopathy or Cardiomyopathy
  - Multisystem disease: D109H; R120G
- Onset: Early to middle adulthood
- Progression: Slow; Sudden cardiac death
- Weakness
  - Proximal: Most patients
  - Distal: Legs; Most patients
  - Cranial nerve: Face, Bulbar (Dysphagia; Dysarthria)
  - Respiratory: Later in disease course
- Chest pain
- Cardiac: Arrhythmia, Conduction block, Congestive failure
- Other systems
  - Lens opacities: Posterior polar cataracts
  - Intestinal malabsorption
- ± Neuropathy
Laboratory
- Serum CK: Normal to 7x normal
- EMG: Myopathic; Irritable
Muscle pathology
- Myopathic
  - Varied fiber size
  - Scattered degenerating & necrotic fibers
- Accumulations of granulofilamentous material in muscle & heart
  - Present in type 1 & 2 fibers
  - Subsarcolemmal & intermyofibrillar
  - Contain phosphorylated desmin
  - Molecular components: Desmin, aB-crystallin, Myotilin, Dystrophin, NCAM, CDC2 kinase
  - Molecules not present: Ubiquitin, Gelsolin, and α1-antichymotrypsin
  - Rubbing out of intermyfibrillar network in type I fibers
  - Trichrome: Regions of dark blue staining
  - Congo red: Some regions congophilic
- Autophagocytosis
- Nuclei: 7% to 8% show early apoptotic changes
- Denervation: Scattered esterase+ angular muscle fibers
- NOTE: αB-crystallin also accumulates in muscle fibers in inclusion body myositis
CRYAB Variant syndrome: Fatal infantile hypertonic myofibrillar myopathy, Recessive
- Epidemiology: Canadian aboriginals
- Genetics: 1 bp deletion; 60delC
- Clinical
  - Stiffness
    - Limb & Axial
    - Progressive
  - Respiratory insufficiency
  - Death: Infancy to 3 years
  - Cognition: Normal
- Laboratory
  - Serum CK: 15x to 25x high
  - Brain MRI: Normal
  - Heart: Usually normal
- Muscle
  - Fiber size: Varied
  - Endomysial connective tissue: Increased
  - Gomori trichrome: Dark-staining inclusions
  - Myofibrillar myopathy: Patchy cytoplasmic desmin staining
  - CRYAB: Reduced staining; Staining peresent for AA 1-10
- Heterozygous parents: Usually not affected
CRYAB Variant syndromes: Other recessive
- Mutations: R56W, S115fs129X, S21Afs24X
- Clinical
  - Cataracts
  - Myopathy: Early onset

Myofibrillar myopathy 4 (MFM4)

⁴⁴
● ZASP (Lim domain-binding 3 (LDB3))

; Chromosome 10q23.2; Dominant

Genetics
- 16 exons: Several tissue specific splice variants
- Mutations: Missense
  - A147T and A165V: Myopathy; Near or within motif important in linking ZASP to Z-disk
  - R268C: Exon 9; Oldest at myopathy disease onset
  - Cardiomyopathy: Mutations
    - Often in linker region between the PDZ and LIM domains
    - Exon 4: Isolated non-compaction of the left ventricular myocardium (INLVM)
    - Exon 6: INLVM or Dilated cardiomyopathy
    - Exon 10: Dilated cardiomyopathy
- Allelic disorders
  - Myofibrillar myopathy 4 (MFM4)
  - Markesbery distal myopathy
  - Dilated cardiomyopathy (CMD1C)
  - Isolated non-compaction of left ventricular myocardium
  - Hypertrophic cardiomyopathy 24 (CMH 24)
- ~16% of myofibrillar myopathies
ZASP protein (Z-band alternatively spliced PDZ motif-containing protein)
- Subcellular localization: Cytoplasm
- Tissue expression: Predominantly in cardiac & skeletal muscle.
- Binds to: α-actinin (Structural component of Z-filaments that cross-links thin filaments of adjacent sarcomeres)
- Structure
  - N-terminal PDZ domain: Important for protein�protein interactions
  - ZASP-like motif (ZM motif): In exons 4 and 6; 26-residues; Needed for interaction with α-actinin
  - Long isoforms: Contain LIM domains that interact with protein kinase C subtypes
- Splice variants
  - Skeletal muscle: 3 isoforms
    - Longest isoform: Lacks exons 4 and 9
    - 2nd long isoform: Lacks exons 4, 9, and 10
    - Short isoform: Lacks exon 4; Stop codon in exon 9
  - Cardiac muscle isoforms
    - Often contain exon 4 instead of exon 6
    - Mutations in exon 6 cause cardiomyopathy in humans
Clinical
- Onset
  - Age: Child to 73 years
  - Weakness: Most common early feature
- Weakness: May be proximal or distal
  - Proximal or Distal
    - Proximal > Distal (45%)
    - Proximal + Distal (27%)
    - Distal only (9%)
    - Proximal only (18%)
  - Legs: Posterior
  - Scapular, Selective: 1 patient
  - Respiratory: Not prominent
- Cardiac (27%)
- Polyneuropathy (45%)
Laboratory
- Serum CK: Normal to 6x elevated
- EMG: Myopathic; Irritable (Fibrillations & Myotonic discharges)
- Muscle pathology
  - Trichrome stain: Pleomorphic hyaline, granular & amorphous deposits
  - Congo red: Hyaline structures often Congophilic
  - Abnormal fiber regions wthout oxidative enzyme activity
  - Vacuoles: Small, Few fibers
  - Partial denervation & reinnervation: Some biopsies
  - Necrosis or Regeneration: Common
  - Chronic changes: Splitting; Internal nuclei
  - Immunocytochemistry: Aggregates may contain Myotilin, Desmin, αB-Crystallin, Dystrophin, NCAM
  - Ultrastructure: Z-disk streaming & disintegration; Disorganized sarcomeres & myofibrils
- MRI
Mouse variant: ZASP deletion (Cypher or Oracle)
- Causes skeletal & cardiac myopathy with fragmented Z-disks

Myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy (ARVD7)

¹⁴
● Desmin (DES)

; Chromosome 2q35; Dominant

Epidemiology: Swedish family
Genetics
- Previously localized to 10q22.3
- ARVD7
- Allelic with: Desmin myopathies
Clinical
- Onset: Adult; 20 to 60 years
- Intrafamilial variability inn severity
- Weakness
  - Mild: Axial
  - Moderate: Distal predominant
  - Severe: Generalized
  - May be asymmetric
- Cardiac
  - Episodes of chest pain or palpitations
  - Cardiomyopathy
    - Arrhythmia: Nonsustained ventricular tachycardia; Atrial flutter
    - Ventricular dilation: Especially Right
Serum CK: Mildly elevated in 50%
EMG
- Myopathic: Proximal & Distal
- Spontaneous activity: Fibrillations; Positive sharp waves
Muscle pathology
- Myopathic
  - Fiber size: Varied
  - Internal nuclei
  - Endomysial connective tissue: Increased
- Myofibrillar disorganization (NADH stain)
- Rimmed vacuoles
- Protein accumulation
  - Desmin storage
  - NCAM upregulation: All fibers in severe patients
- Ultrastructure
  - Intermyofibrillar accumulation of granulofilamentous material
  - Myofibrillar disorganization
  - Z-band streaming
  - Occasional: Cytoplasmic bodies; Autophagic vacuoles

Desmin-associated restrictive cardiomyopathy ²⁸
● Autosomal Dominant

Onset age
- Variable; 3 to 92 years
- Most with onset by 42 years
- Occasional asymptomatic carriers
Cardiomyopathy
- Restrictive (Reduced myocardial compliance)
- Dyspnea
- Edema: Pleural effusion; Anasarca
- Venous hypertension
- Hepatomegaly
- EKG: Atrial flutter/fibrillation; ST/T wave changes
- Echocardiogram: Atrial enlargement, left & right
- Cardiac biopsy: Interstitial fibrosis
Skeletal muscle: No myopathy
Cataracts: None
Desmin accumulation: Cardiac muscle; Demonstrated by immunocytochemistry

Cardioneuromyopathy with Hyaline masses and Nemaline rods

● Autosomal Recessive

Onset: Adult; 5th decade
Clinical
- Weakness: Distal > Proximal; Respiratory insufficiency
- Cardiomyopathy: Systolic dysfunction; A-V conduction block
- Course: Life span limited by respiratory function
Laboratory
- Serum CK: Normal or high
- Cervical spine: Vertebral fusion
Muscle pathology
- Fiber size: Varied; Small to Hypertrophic
- Hyaline masses
  - Location: Type I muscle fibers
  - Congophilic
  - Contain: Desmin; αB-Crystallin; Ubiquitin; α₁-Antichymotrypsin
- Nemaline rods: Usually in fibers with hyaline masses
- Vacuoles
- Lobulation: Some type I muscle fibers

Desmin myopathy (Type 2)
● Autosomal Dominant

Clinical
- Onset: Child - Adult
- Weakness: Distal & Proximal
- Fatigability
- Dysphagia
- Cardiac: Occasional
Pathology: Cytoplasmic or Spheroid bodies associated with desmin

Congenital muscular dystrophy with Desmin inclusions

● Selenoprotein N, 1 (SEPN1)

; Chromosome 1p36-p35; Recessive

Epidemiology: Northeastern Germany & Polish families
SEPN1 protein
- Description
- Other SEPN1 disorders
  - CM with rigid spine
  - Minicore syndromes
Onset
- Age: Birth or Early infancy
- Hypotonia
Clinical
- Weakness
  - Proximal
  - Axial
  - Face
- Muscle size: Small
  - Thin inner thighs
  - Straight calves
  - Flat feet
- Cardiac
  - Right ventricular hypertrophy
  - Cardiac failure in 1st 2 decades
  - Normal in some families
- Scoliosis
  - Dorsal lordosis
  - Trunk deviation: Lateral
  - Hips: Balanced
  - Spine rigidity
  - Onset: 8 to 14 years
- Joint contractures: Correlate with degree of weakness
- Course
  - Weakness: Progressive
  - Death: May occur in 1st or 2nd decade due to respiratory failure or pneumonia
Laboratory
- Serum CK: Normal or Mildly high
- Serum aldolase: Normal or Mildly high
Muscle pathology
- Desmin-containing inclusions
  - Present in 10% of muscle fibers
  - Mallory body-like
  - Immunoreactive for: Desmin; Dystrophin; Ubiquitin
  - Ultrastructure: Composed of helical filaments, 10 to 12 nm diameter
- Fiber size variability
- Internal nuclei
- Vacuoles: Occasional rimmed
- Connective tissue: Mildly increased
- Type I muscle fiber predominance

Myofibrillar myopathy 5 (MFM5)

⁴⁷
● Filamin C (Filamin 2; FLNC)

; Chromosome 7q32.1; Dominant

Epidemiology: German & Chinese families
Genetics: Truncation mutation
- Mutations
  - German: W2710X
  - Chinese: 2695�2712 del/GTTTGT ins (Exon 18; In-frame)
  - 12-nucleotide deletion in exon 18
  - Filamin C rod & dimerization domains
- Truncated protein: Abnormal folding; Unable to dimerize properly
- Allelic disorders
  - Distal myopathies
    - Distal myopathy with Spared anterior leg muscles (Williams myopathy)
    - Distal myopathy with Upper limb predominance
  - Cardiomyopathy, familial hypertrophic, 26 (CMH26)
  - Myofibrillar myopathy 5 (MFM5)
Filamin C protein
Clinical

Onset
- Age: 35 to 57 years
- Weakness: Usually proximal legs
- Back pain
Weakness
- Legs > Arms
- Usually: Proximal > Distal
- Respiratory: 50%
- Other: Hands; Calf weakness, Selective; Neck flexor
Polyneuropathy: 40%
Cardiac
- Some patients
- Often mild
- Bundle branch block; Reduced ejection fraction
GI: Chronic diarrhea in some patients

Laboratory
- Serum CK: Mildly elevated, 2x to 8x
- EMG: Myopathic; Myotonic discharges
- Muscle pathology: Myofibrillar myopathy
  - Internal nuclei
  - Fiber splitting
  - Necrosis: Isolated fibers
  - Gomori trichrome stain: Hyaline masses; Vacuoles; Rods
  - Aggregates
    - Contain: Filamin C, Desmin, Myotilin, Dystrophin, Sarcoglycans; Dysferlin; Not α-actinin
    - Cytoplasmic
    - Spheroid bodies

Myofibrillar myopathy 6 (MFM6)

⁶⁸
● BCL2-associated athanogene 3 (BAG3)

; Chromosome 10q25.2-q26.2; Dominant

Epidemiology: 2 families
Genetics
- Mutation: Pro209Leu in both families
- Allelic disorders
  - CMD 1HH, Cardiomyopathy, Familial dilated
  - Polyneuropathy, Demyelinating
  - CMT2
Protein: Family of Hsp70/Hsc70 molecular chaperone regulators
- Anti-apoptotic activity
  - Binds to Bcl-2 and PLC-γ
- Chaperones
  - Binds to the ATPase domain of HSP70 & HSC70 chaperones
  - Inhibits chaperone activity of HSP70 & HSC70: Promotes substrate release
- Muscle: Z-disk (Colocalizes with myotilin)
Clinical
- Onset: Childhood
- Weakness
  - Proximal > Distal
  - Limb & Axial
  - Respiratory
- Cardiomyopathy
  - Onset: Teens
  - Restrictive or Hypertrophic
- Skeletal
  - Rigid spine
  - Scoliosis
  - Contractures
- Polyneuropathy (1 patient)
  - Axonal & Demyelinating
  - Some Giant axons
Laboratory
- Serum CK: High, 3- to 15-fold
- EMG: Myopathic
- Muscle
  - Histology
    - Fiber size: Varied
    - Splitting
    - Necrosis & Regeneration
    - Abnormal staining: Bag3, αB-crystallin, Desmin, Gelsolin, NCAM, Myotilin, Ubiquitin, Dystrophin
    - Other immunoreactivity in muscle fibers: Hsp27, HspB8, Bcl-2
    - Congophilia
  - EM
    - Z-disk disintegration
    - Accumulation of granualar debris & larger inclusions
    - Apoptosis
  - BAG3: Abnormal aggregation
BAG3 Variant: Dilated cardiomyopathy
- Mutations: Frameshift, Deletion, Nonsense & Missense
- Adult onset
BAG3 Variant: CMT2 ¹⁰⁸
- Epidemiology: 2 families, 5 patients
- Genetics
  - Inheritance: Dominant
  - Mutation: c.625C>T; p.Pro209Ser
- Clinical
  - Onset ages: Adult; 3rdc to 5th decade
  - Weakness: Distal; Legs > Arms
  - Sensory loss: Pan-modal; Legs; Distal
  - Dyspnes: 5th decade
- Laboratory
  - Electrodiagnostic
    - NCV: Velocity nomal
    - Axon loss: Low amplitude CMAPs & SNAPs
  - Serum CK: Normal or Mildly high

Desmin disorders: Other

Desmin knockout mouse
- Exercise intolerance
- Cardiomyopathy: Dilated; Cardiomyocyte hypertrophy
- Skeletal myopathy
  - Location: Weight-bearing muscles & Diaphragm
  - Anatomy: Loss of anchorage of myofibrils to plasma membrane at costameres
- Vasculopathy: Lower passive & active tension in vessel walls
- Life span: Shortened
- Regeneration: Adipocytes tend to accumulate
Desmin-containing inclusions
- Scapuloperoneal muscular dystrophy
- Inclusion body myositis
- Enlinafide (Topoisomerase II inhibitor; Cancer chemotherapy) myopathy ¹²
- Emetine: Painful myopathy ± Rhabdomyolysis

Intermediate filaments & Disorders ²⁰

General features
Proteins & Mutations

Intermediate filaments: General features
- Family
  - ~ 65 functional genes
  - Most are unique to multicellular organisms
  - ? Ancestor protein in unicellular organism: Crescentin (In bacteria)
- Structure
  - Fibrous proteins
  - Central rod domain
    - Coiled coil α-helical
    - Similar structure in most IFs: Different 1° sequences
    - Heptad repeats: Contain Acidic residues
  - amino- & carboxy- termini: Various lengths and sequence
  - 10-nm diameter
  - Soluble unit: Tetramer with two antiparallel dimers
- Post-translational modifications
  - Farnesylation
  - Phosphorylation: Regulates
    - Filament organization & solubility
    - Association with interacting proteins
    - Susceptibility to degradation during apoptosis
  - Glycosylation
  - Transglutamination:
    - Formation of protective, cornified cell envelope contributing to skin barrier
- Interactions with other proteins
  - Actin microfilaments (7 nm)
  - Microtubules (24 nm)
- Locations
  - Most are cytoplasmic
  - Lamins in nucleus
  - Some are integral membrane proteins
- Functions: Mediate cell-type-specific features of cytoarchitecture
  - Interconnected: With same, or other accessory proteins
  - Form cytoskeletal scaffolding in eukaryotic cells
  - Dynamic: Some are motor proteins
  - No known enzymatic activity
- Mutation effects
  - Often disrupt aggregation of intermediate filament proteins
- Neurofilaments ¹⁰⁷
  - General
    - Major intermediate filament in neurons
    - Up to 85% of protein content
  - Composition: Usually 4 subunits
    - NF subunits have tripartite structure
      - Central α-helical rod region
        
        Conserved
        
        Shared with other IF family proteins
        
        Contain long stretches of hydrophobic heptad repeats
      - Head domain at amino-terminal
        
        Variable
        
        Rich in serine & threonine residues
        
        Contains consensus sites for O-linked glycosylation or phosphorylation
      - Tail domain at carboxy-terminal
        
        Repeats of Lys�Ser�Pro ("KSP") motif: 6 to 15 in NF-M; 40 to 51 in NF-H
        
        Longer in NF-H & NF-M than in other intermediate filaments
    - Proteins
      - NF light chain (61.5 kDa; 68 on SDS-PAGE): Forms backbone & initiates assembly of NF
      - NF medium chain (102.5 kDa; 160 on SDS-PAGE)
      - NF heavy chain (112.5 kDa; 200 on SDS-PAGE)
      - α-internexin: CNS neurons
      - Peripherin: PNS neurons
    - Subunits form heteropolymers to assemble into 10 nm filaments
  - Structure: Carboxy terminals of NFH & NFM form side arm projections
    - Allow interactions among neurofilaments
    - Underlie the "cross links" between adjacent filaments
    - KSP (Lys-Ser-Pro) repeat motif: Size is ALS risk factor
  - Location
    - Exlusively in neurons
      - Perikarya: Sparse & Tortuous
      - Dendrites: Sparse & Tortuous
      - Axons
        
        Numerous
        
        Straight & Unbranched
        
        Long (mean 118 mm)
        
        Peripheral axons: 2x more in proximal than distal axons
        
        Optic nerve axons: 3x more in distal than proximal axons
      - Large myelinated axons
        
        Organization: Parallel arrays
        
        Distance from each other: Determined by side arms projecting perpendicularly from filament core
        
        Increase in number proportionate to radial growth of axon
        More concentrated at: Nodes of Ranvier; Demyelinated regions of axons
  - Metabolism
    - Half-life: 55 days
    - Degradation: Multiple systems
    - NF assembly: Confers proteolytic resistance
  - Axon transport
    - Most NF network is stationary in axons
    - Small proportion of NF moves down axon by slow transport
    - Subunits required for NF transport: NF-M or α-internexin
    - Nonfilamentous heterooligomers assemble into filaments as they are transported
    - Motors
      - Anterograde transport: Kinesin-I
      - Retrograde transport: Dynein�Dynactin complex
    - Reduced NF transport
      - Toxin: IDPN
      - NF-H: Increased phosphorylation
  - IF association molecules
    - Plectin; BPAG1
    - Mediate the cross-linking of NF & microtubules
    - Produce the cytoskeletal lattice
    - Cross bridges associated with
      - Actin filaments
      - Microtubules
      - Cross bridge proteins: Spectrin; Bullous pemphigoid antigen; Plectin; tau; MAP1; MAP2
  - Post-translational modifications
    - Phosphorylation
      - Location
        
        40 to 70 Lys-Ser-Pro (KSP) repeats
        
        C-terminus domains
      - Mediated by
        
        Protein kinase A (PKA)
        
        Protein kinase C (PKC)
        
        Calcium/calmodulin-dependent protein kinase type II (CAMKII)
      - Probable roles
        
        NF assembly & disassembly
        NF transport from perikaryon to the axon through slow transport mechanisms
        
        NF incorporation into a cytoskeletal network
    - O-linked N-acetylglucosamine (O-GlcNAc)
  - NF functions
    - Determine axonal caliber & conduction velocity
      - Neurofilament numbers
      - Tail domains of NF-H & NF-M
    - Structural support & docking sites for reversible interactions with vesicular organelles & molecular motors
    - Synaptic plasticity
  - Neurofilament Disorders: NF-L; NF-M; NF-H
    - Genetic
      - ALS, Sporadic & Familial
        
        NF-H tail deletions
        
        Peripherin
      - CMT: NF-H
      - CMT: NF-L
        
        1F
        
        2E
        
        AR (2B5)
        
        Mutations may be in head, coil or tail domains
      - Mutations in associated proteins
        
        AR-CMT: TRIM2 - NFL are target of ubiquitination
        CMT 2F/dHMN: HSPB1
        CMT 2B: RAB7A
        Giant axonal neuropathy: Gigaxonin - Impaired NF degradation
        ALS: SOD1
        Dementia/Parkinsonism: PRKAR1B
      - Linkage to CNS disorders
        
        Parkinson disease: NF-M rod domain point mutations
        Alzheimer disease: NF-M & NF-H mutations; Hyperphosphorylation of KSP domains
    - Immune Polyneuropathy: Anti-Neurofilament Antibodies
    - Toxic polyneuropathies
      - β,β-Iminodipropionitrile: Rat models
      - 2,5-Hexaneidone (Glue-sniffing)
      - DMAPN
    - CSF NF levels: May be abnormal in ALS, Parkinson disease
    - Pathology: Accumulations in axons
Intermediate filament proteins & mutations
- α-Internexin : Neurons
- Keratin family: Epithelial cells; > 20 proteins
  - Protect from mechanical & nonmechanical forms of stress
  - Numerous Keratinopathies
    - Epidermolysis bullosa & hyperkeratosis syndromes
    - Corneal dystrophy: Keratins 3 & 12
    - Alopecia (Monilethrix): Hair keratins 1 & 6
    - Pachyonychia congenita: Keratins Keratins 6a, 16, 6b, 17
- Desmin (2q35): Dominant myopathy
  - Myopathy + Right ventricular cardiomyopathy
- Desmuslin : Muscle; Co-localizes with desmin
- Filensin : Lens; Cataracts
- FHL1: Scapuloperoneal muscular dystrophy
- Glial fibrillary acidic protein (GFAP) : Alexander disease
- α-Internexin : CNS
- Lamins: Nuclear
  - Lamin A/C: Emery-Dreifuss muscular dystrophy; Differentiated cells
  - Lamin B : All cell types
- Nestin : Neuroepithelial stem cells; Muscle cells (Z-band); Fibroblasts
- Neurofilaments: NF-L; NF-M; NF-H
- Paranemin : Muscle cells; Co-polymer with desmin
- Peripherins: Neuronal cells
  - Peripheral nerve : Sporadic ALS
  - Photoreceptor : Retinitis pigmentosa; Macular dystrophy
- Phakinin : Lens; Co-polymer with Filensin
  - Juvenile & Congenital cataract
- Syncoilin: Muscle, Cardiac & Skeletal
- Synemin : Muscle cells; Co-polymer with desmin
- Titin: Proximal & Respiratory muscle weakness
- Vimentin : Mesenchyme; Null mutation has no phenotype
Intermediate filament-associated proteins & mutations
- αB-crystallin (11q22): Dominant myopathy
- Bullous pemphigoid antigen 1
- Desmoplakin : Keratosis palmoplantaris striata II; Cardiomyopathies
- Emerin: Emery-Dreifuss muscular dystrophy
- Gigaxonin: Giant axonal neuropathy
- Plectin: Congenital Muscular Dystrophy with Familial Junctional Epidermolysis Bullosa
Neurofilament accumulations in acquired neuropathies
- Giant axonal neuropathy
- Hexacarbon intoxication
- Disulfiram
- Acrylamide
- β,β-iminodipropionitrile (Proximal initial axon segments; Animal model only)
- Dimethylaminopropionitrile (Distal intramuscular nerves)
- Carbon disulfide
- Diabetes (Distal intramuscular nerves)
- Non-specific: Chronic neuropathy
- Motor neuron disease (ALS): Cell body & Initial segment
Other
- α-Actin: Nemaline (Rod) Myopathy
- Dystrophin: Duchenne muscular dystrophy

CYTOPLASMIC BODY MYOPATHIES (Also see Distal myopathies)

Severe limb-girdle: ? Recessive
Mild limb-girdle: Dominant
Desmin myopathies
Myopathy + Respiratory weakness
Type 1: Titin; 2q31; Dominant
Type 2: 2q21; Dominant
Distal: Dominant
Gowers-Laing: MYH7; 14q12
Plectin deficiency
Congenital
ACTA1: 1q42

Pathology
Cytoplasmic bodies

Gomori trichrome

Phalloidin

Severe limb-girdle type
● ? Recessive
- Clinical features
  - Onset: Infancy or childhood
  - Hypotonia & proximal weakness; Skeletal abnormalities
  - Respiratory insufficiency
  - Death: Early adulthood
Mild limb-girdle type
● Autosomal Dominant
- Clinical features
  - Onset: Adolescence
  - Slowly or non-progressive limb-girdle weakness
Myopathy with Proximal Weakness, Early Respiratory Failure & Cytoplasmic aggregates (HMERF) ⁶
● Titin (TTN) ; Chromosome 2q31.2; Dominant
Myopathy with Proximal Weakness and Early Respiratory Muscle Involvement (Type 2) ⁹
● Chromosome 2q21; Dominant
- Epidemiology: French families
- Clinical
  - Onset: Adult; 18 to 40 years
  - Weakness
    - Proximal: Upper & lower extremities
    - Respiratory: Diaphragm; Early
- Laboratory
  - Serum CK: Normal
  - Pathology
    - Cytoplasmic bodies containing actin & desmin in type I muscle fibers
    - Ultrastructure: Thin filaments & Dense material related to Z-discs.
Cytoplasmic Body Myopathy: Distal types
● Autosomal Dominant
- Also see: Gowers-Laing, severe phenotype (MYH7)
- Clinical features
  - Weakness
    - Distal & Proximal weakness
    - Onset in hands
  - Onset: Late 40 to 50 years
  - Progression: To respiratory failure
  - Cardiomyopathy: Heart block; Arrhythmias; Congestive heart failure
- Laboratory
  - Serum CK: Nomal or slightly elevated
  - EMG: Myopathic; Complex repetitive discharges
  - Muscle pathology
    - Cytoplasmic bodies
    - Myofibrillary inclusions in cytoplasm of Type I muscle fibers
Cytoplasmic Bodies: Pathology

MYOPATHIES WITH TUBULAR AGGREGATES

General features
Pathology
Syndromes
Myopathy, Proximal
TAM1: STIM1; 11p15; Dominant
TAM2: ORAI1; 12q24; Dominant
TAM (VMCQA): CASQ1; 1q23; Dominant
Myasthenic disorders
Limb Girdle MG 1: GFPT1; 2p13; Recessive
Limb Girdle MG 2: DPAGT1; 11q23; Recessive
CMS 14: ALG2; 9q22
Slow channel MG: AChR mutations
Rhabdomyolysis & Cramps
PGAM2; 7p13; Recessive
Neuromuscular, Other
Gyrate atrophy: OAT; 10q26; Recessive
Periodic paralysis
Hypokalemic
Andersen
Paramyotonia congentia: Some patients
Occasional: Differential Diagnosis

Gomori trichrome

Tubular aggregates: General features

Serum CK: Normal or Mildly high
Muscle pathology ⁴⁹
- Histochemical staining
  - Positive: NADH-TR (blue); Gomori trichrome (Red); AMPDA; Esterase; Sudan black
  - Negative: SDH in most cases, especially small tubular aggregates
  - Fiber type association
    - Usually more frequent, or larger, in type 2 fibers
    - May occur only in type 2 fibers or in both types
    - STIM1: Type I & 2 fibers
    - ORAI1: Type I fibers
  - Locations
    - Subsarcolemmal: Most common
    - Internal regions of muscle fibers: Some TAs
  - Differential diagnosis: Cylindrical spirals
- Subgroups
  - Myopathies with large tubular aggregates (One ≥ 125 µm²)
    - Fiber type: 2 & some 1
    - Family history: 50%
    - Associated disorders: Uncommon
  - Myopathies with small tubular aggregates (All < 125 µm²)
    - Fiber type: 2
    - SDH negative
    - Family history: Unusual
    - Asscociated disorders: Common
- Clinical features: Associated
  - Similar onset age & disease duration in both subgroups
  - Limb weakness 50%
  - Myalgia 40%
  - Fatigability 30%
  - Cramps 20%
- Ultrastructure
  - Cytoplasmic aggregates of membranous tubules
  - Aggregates: Size = 50 to 70 nm tubules
  - Enclose smaller tubule or flocculent material
  - Derived from: Sarcoplasmic reticulum (Dilated terminal cisternae)
- Protein constituents
  - Common: Calsequestrin; SR Ca⁺⁺ ATPase (SERCA, usuallly same isoform as rest of fiber); Dihydropyridine receptor (DHPR);
    RYR1; Triadin; STIM1; Heat shock proteins; Dysferlin; Tau; Ubiquitin; Emerin (Rare)
  - Not present: Dystrophin; Sarcoglycans; Desmin

Tubular aggregates: Proximal myopathy syndromes

Proximal myopathy with Tubular Aggregates, Younger onset ± Ophthalmoplegia (TAM1) ⁸⁶
● Stromal interaction molecule (STIM1) ; Chromosome 11p15.4; Dominant
- Epidemiology: 13 families
- Genetics
  - STIM1 mutations
    - Heterozygous
    - Missense
    - His72Gln; Asn80Thr; Asp84Gly; Leu96Val; Phe108Ile; Phe108Leu; His109Asn; His109Arg
  - Mutation location: Calcium-binding EF hand domains
  - Mutation effect: Induces STIM1 oligomerization
  - Allelic with
    - Childhood immune deficiency: Recessive
    - Stormorken syndrome: Dominant
- STIM1 protein
  - Single transmembrane protein
  - Location: Endoplasmic reticulum (ER)
  - Function: ER Ca⁺⁺ sensor
    - EF hand motif: Senses & binds Ca⁺⁺
    - Ca⁺⁺ unbound: STIM1 unfolds & oligomerizes via SAM domains
    - Oligomerization
      - Activates Ca⁺⁺-release-activated Ca⁺⁺ channels (CRACs) by direct binding to subunit ORAI1
      - Triggers extracellular Ca⁺⁺ entry
  - Other ER Ca⁺⁺ sensor protein: STIM2
- Clinical
  - Onset
    - Age: Childhood to Early adult
    - Weakness: Falling, or Difficulty running or Climbing stairs
    - Some patients: Myalgias or Asymptomatic with high CK
  - Weakness
    - Proximal
    - Legs > Arms
    - Slowly progressive: Some patients use cane in 6th decade
    - Respiratory: Varied; VC 49% of predicted to Normal
    - Face: Usually normal
    - Strength normal in some patients
  - Muscle size
    - Atrophy: Quadriceps (50%)
    - Hypertrophy: Calf
  - Myalgias
  - EOM limitation: 50% of families
    - Up-gaze
    - No ptosis
  - Contractures: Ankle; Wrist; Fingers; Knees; Neck
  - Cardiac: Normal
- Laboratory
  - Serum CK: High; 4x to 27x normal
  - EMG : Myopathic
  - Muscle Pathology
    - Tubular aggregates
      - Stain with: Gomori trichrome; NADH; Not SDH
      - In both Type I & II muscle fibers
      - Vesicular membrane collection
      - Contents: Empty or moderately dense flocculent material
      - Protein constituents
        
        Aggregates: SERCA1; Triadin
        
        Periphery: RYR1; STIM1
      - Ultrastructure: Single- or double-walled membranes of different diameters
      - Differential diagnosis
    - Internal nuclei
    - Type 2 muscle fiber atrophy: Most patients
  - Hematology: Normal
- STIM1 variant syndrome: Childhood immunodeficiency 10 (IMD10)
  - STIM1 mutations: Recessive loss of function
  - Immune effects: T-cell inactivation
  - Other clinical: Hypotonia
  - Muscle: Type 2 fiber atrophy
- STIM1 variant syndrome: Stormorken syndrome (STRMK)
  - Epidemiology: 6 families
  - Genetics
    - Mutation: R304W (Cα2 helix); Gain of function
  - CRAC channel effect: Constitutive activation
  - Clinical
    - Weakness
    - Hematology: Bleeding diathesis
    - Miosis
  - Laboratory
    - Myopathy with tubular aggregates
    - Thrombocytopenia
    - Functional asplenia
    - Serum CK: High, 1600 to 3800
Myopathy with Tubular Aggregates & Miosis (TAM2) ⁸⁶
● Orai calcium release-activated calcium modulator 1 (ORAI1) ; Chromosome 12q24.31; Dominant
- Nosology: Stormorkin-like
- Epidemiology: 4 families, 9 patients
- Genetics
  - Mutation: P245L
- ORAI1 protein
  - Plasma membrane
  - Store-operated calcium entry
  - Calcium release-activated calcium (CRAC) channel
  - Interacts with: STIM1
- Clinical
  - Onset age: Childhood to Adult
  - Weakness: Proximal; Distal with disease progression
  - Tendon reflexes: Absent in legs
  - Contractures: Ankles
  - Eyes
    - Pupils: Miosis, Congenital
    - Night vision: Reduced
- Laboratory
  - Serum CK: 500 to 800
  - Muscle
    - Fiber size: Varied; Atrophy
    - Fiber types: May be type I predominance
    - Tubular aggregates
      - In type 1 fibers
      - Differential diagnosis
Proximal myopathy with Tubular Aggregates, Adult onset
● Autosomal Dominant ²⁴
- Onset: 5th & 6th decade
- Weakness: Proximal ± Distal
- Discomfort
  - Muscle pain, cramps
  - Siffness: Exertional
- Progression: Slow
- Serum CK: Normal or Mildly high
- Pathology
  - Tubular aggregates
    - In type II muscle fibers
    - Tubule types: Several
  - Type II atrophy
Proximal myopathy with Tubular Aggregates, Younger onset
● Sporadic or Recessive
- Male > Female
- Clinical
  - Onset: Teens
  - Weakness: Proximal
  - Progression: Slow
- Laboratory
  - Serum CK: Normal or Mildly high
  - Pathology: Tubular aggregates in II > Type I muscle fibers

Tubular aggregates: Other Neuromuscular Disorders

Congenital MG with Tubular Aggregates
- Familial Limb Girdle Myasthenia with Tubular Aggregates: GFPT1; 2p13; Recessive
- Familial Limb Girdle Myasthenia with Tubular Aggregates 2: DPAGT1; 11q23; Recessive
- CMS14: ALG2; 9q22; Recessive
- Slow AChR channel syndrome: AChR subunit mutations; Usually Dominant
Exercise induced muscle pain & stiffness
● Sporadic or Dominant
- Male > Female
- Clinical
  - Onset age: Childhood or Adult
  - Discomfort
    - Muscle pain: Aching & Stiffness
    - Cramps
    - Increased by exercise: may last up to 36 hours
    - Legs > Arms
  - Weakness: Minimal or None
- Laboratory
  - Serum CK: Mildly high, especially after exercise
  - EMG: Normal or Myopathic
Periodic paralysis: Hypokalemic
Gyrate atrophy of choroid and retina (GACR) ⁶¹
● Ornithine aminotransferase (OAT) ; Chromosome 10q26; Recessive
- Epidemiology
  - Common in Finnish families (Arg180Thr)
  - Many other cases
- Genetics
  - Mutations: Missense & few truncation
- Ornithine-amino-transferase protein
  - Mitochondrial enzyme: Mitochondrial matrix
  - L-ornithine + a 2-oxo acid = L-glutamate 5-semialdehyde + an L-amino acid
- Clinical
  - Visual loss
    - Onset: Late childhood; Night-blindness
    - Blindness by 5th decade
    - Gyrate atrophy of choroid & retina
  - Myopathy
    - Weakness: Proximal
    - Atrophy: Glutei
    - Scapular winging
    - Some patients: No muscle symptoms
    - Muscle pathology
      - Type 2 atrophy
      - Tubular aggregates
  - CNS: Mental retardation
- Laboratory
  - Serum: Hyperornithinemia
  - Brain MRI: Atrophy; White matter lesions
  - EEG: Slowing
- Treatment
  - Pyridoxine: 20 mg to 600 mg; No effect on visual loss
  - Reduced arginine in diet

Tubular aggregates: Other occasional associations

Myotonias
- Myotonia congenita
- Paramyotonia congenita: SCN4A
Malignant hyperthermia
Myositis
Alcoholic myopathy
Whipples disease
Porphyria cutanea tarda
Phosphoglycerate mutase M deficiency: Atypical ultrastructure
Serum CK high: Idiopathic

Tubular Aggregates: Mouse models

MRL +/+ males: Tubular aggregates
- Number & size increases with age
- Castration prevents formation
Creatine kinase knockout mice

Myopathy with Tubular Arrays ⁴⁸

Epidemiology: 3 patients: Father & Son + Sporadic
Clinical
- Onset: 1st to 7th decade
- Weakness
  - Legs > Arms
  - Proximal
- Muscle bulk: Reduced
- Discomfort: Myalgias
Laboratory
- Serum CK: Normal
- EMG: Myopathic
Muscle pathology: Inclusions
- Eosinophilic; Mildly refractile; Type 2 fibers; Gomori trichrome +
- Ultrastructure: Rounded hexagonal tubular arrays

Myopathy, vacuolar, with CASQ1 aggregates (VMCQA)

⁹⁴
● Calsequestrin 1 (CASQ1)

; Chromosome 1q23.2; Dominant

Nosology
- Calsequestrin Aggregate Myopathy
- Protein Surplus Myopathy
Epidemiology: 30 patients
Genetics
- Mutations: Asp244Gly (Most patients) Gly103Asp
Calsequestrin-1 protein
- Ca⁺⁺ binding protein: High capacity, Moderate-affinity
- Main Ca⁺⁺ buffer of sarcoplasmic reticulum (SR) of cardiac & skeletal muscle
- Part of multiprotein complex with
  - SR Ca⁺⁺ release channel (ATP2A1; SERCA1)
  - Ryanodine receptor 1
- Participates in excitation-contraction coupling
  - Links T-tubule membrane depolarization to activation of Ca⁺⁺ release from SR
  - Localization: Triads (Ca⁺⁺ release units)
  - Muscle relaxation
Clinical
- Onset age: 4th to 6th decade
- Discomfort
  - Myalgias
  - Cramps
  - Fatigue
  - Exercise intolerance
- Weakness
  - Mild or None
  - Legs > Arms
  - Proximal
- Cardiac: Subclinical changes
- Some patients: Asymptomatic
Laboratory
- Serum CK: High, 2x to 25x normal
- EMG: Myopathy
- Muscle MRI
  - Fibrofatty substitution
  - Asymmetry
  - Early: Vastus lateralis (Distal), Semitendinosus, Gluteus maximus
  - Thigh: Anterior > Posterior
  - Upper limbs: Mild changes
- Muscle
  - Vacuoles: Round; Clear; Type 2B fibers; Surrounded by desmin
  - Inclusions
    - Plastic sections: Quadrangular or Rectangular
    - Staining: SERCA1; Calsequestrin-1; RyR1
    - Ultrastructure: Electron dense inclusions in sarcoplasmic reticulum; Triads abnormal
  - Necrotic muscle fibers: Scattered
  - Tubular aggregates: 2 families & Gly103Asp mutation
    - Contain: Calsequestrin, STIM1, RyR1

Congenital Myopathy Syndromes: Late onset or progressive

Animal models with Myopathy

Type XV collagen (COL15A1) deficiency
- Myopathy: Skeletal & Cardiac
- Collapsed capillaries: Endothelial cell degeneration
Cypher : Congenital myopathy, severe
myd mouse
- Mutations in LARGE
  - Intragenic deletion of exons 4-7
  - Protein class: N-acetylglucosaminyltransferase
  - Also see: Congenital muscular dystrophy (MDC1D)
- Clinical
  - Abnormal gait & posture, elevated
  - Sensorineural deafness
  - Brain defects: Similar to Fukuyama & Muscle-Eye brain CMD; Type II lissencephalic
- Laboratory
  - Serum creatine kinase: High
  - Muscle pathology: Dystrophic; Reduced α-dystroglycan

Also see: Other Dystrophies

MUSCULAR DYSTROPHY SYNDROMES 2