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LIMB-GIRDLE MUSCULAR DYSTROPHY (LGMD) SYNDROMES^²

Limb girdle dystrophies: Dominant
1A: Myotilin; 5q31; Dysarthria
1B: Lamin A/C; 1q21; + Cardiac
1C: Caveolin-3; 3p25; Child onset
1D: 7q
Dilated Cardiomyopathy (?1E): 6q23
1F: 7q32
1G: 4q21
Ankle contractures & High CK
Bethlem: Collagen VI; 21q22 & 2q37
Central core: Ryanodine receptor (19q13)
Cytoplasmic body: 2q24; 2q21 + Other
Distal myopathies
MPD2: 5q31; ? Same locus as LGMD1A
Emery-Dreifuss
Lamin A/C; 1q21
SYNE1; 6q25
SYNE2; 14q23
Facioscapulohumeral: 4q35
Myofibrillar (Desmin storage)
Desmin: 2q35; AD or AR
αB-crystallin: 11q22
Filamin C: 7q32
LGMD 1A: Myotilin; 5q31
Congenital: SEPN1; 1p36
ZASP myopathy: 10q22
BAG3: 10q25
Other
Myotonic (DM1): DMPK; 19q13
Myotonic (DM2): ZNF9; 3q21
Oculopharyngeal: PABP2; 14q11
Skeletal + Myopathy
Bone fragility: 9p21
Paget disease: VCP; 9p13

Limb girdle dystrophies: Recessive
2A: Calpain-3 ;15q15
2B: Dysferlin; 2p13.1
2C: γ-Sarcoglycan; 13q12
2D: α-Sarcoglycan; 17q21
2E: β-Sarcoglycan; 4q12
2F: δ-Sarcoglycan; 5q33
2G: Telethonin; 17q11-12
2H: TRIM32; 9q31-q33
2I: FKRP; 19q13.3
2J: Titin; 2q24
2K: POMT1; 9q34
2L: 11p13
2M: Fukutin; 9q31
2N: POMT2; 14q24
Merosin (Laminin α2)
Absent: 6q22
Reduced: 6q22
Abnormal: LGMD 2I
Caveolin-3 mutations
Myosclerosis: COL6A2; 21q22.3
Myopathy +
Cardiomyopathy: DPM3; 1q12
Lipodystrophy: PTRF; 17q21

Limb girdle dystrophies: X-linked
Barth: G4.5 (Tafazzins); Xp28
Becker: Dystrophin; Xp21
Duchenne: Dystrophin; Xp21
Emery-Dreifuss: Emerin; Xq28
Manifesting carriers
Dystrophinopathy
Myotubularin
McLeod Syndrome: XK; Xp21.1;
Vacuolar
Danon's disease: LAMP-2; Xq24
Excessive Autophagy: VMA21; Xq28
Mental retardation & Cardiomyopathy

Other inherited myopathy syndromes
Barnes's myopathy
Cardiac + Myopathy
Cardiomyopathy-associated myopathy
Cardiomyopathy (?LGMD1B)
Dilated Cardiomyopathy: 6q23
Congenital
Myopathies: Late-onset
Muscular dystrophies
Cytoplasmic body myopathies
Distal myopathies
Excessive autophagy: Xq28
Familial myasthenia gravis
FSH dystrophy: 4q35
Hereditary IBM syndromes
IBM1: Desmin; 2q35; Dominant
IBM2: GNE; 9p12; Recessive
IBM3: MyHC-IIa; 17p13; Dominant
IBM + Paget disease: 9p13; Dominant
Metabolic myopathies
Glycogen
Lipid
Mitochondrial
Myopathy + PEO: 17p13; Recessive
Myotonic dystrophy
Other dystrophies
Reducing body
Respiratory failure
Scapuloperoneal syndromes
Skeletal + Myopathy
Diaphyseal dysplasia: TGFB1; 19q13
Epiphyseal dysplasia: COL9A3; 20q13
Spheroid body (Myotilin)
Tubular aggregates
Tubular arrays

LGMD: General features

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

DAG complex +

LGMD: General features

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

From Bramwell:
Atlas of Clinical Medicine

MD: Toe walking

Myopathies: General features
Inheritance
- LGMD1: Dominant
- 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
- Muscle hypertrophy
- Cardiomyopathy
- High serum CK: Especially DMD, Sarcoglycanopthies, LGMD 2B
- Rippling muscles: LGMD 1C
- Vacuoles
Subcellular localization of myopathy-related proteins
- Nucleus
- Cytosol
- Golgi
  - FKRP: LGMD2I; Congenital Muscular Dystrophy (MDC1C)
- Myofibrillar
- 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
- Disordered glycosylation of α-dystroglycan³³
  - Fukutin: Congenital muscular dystrophy; LGMD 2L; Cardiomyopathy
  - POMGnT1: Muscle-Eye-Brain disease (Santavuori)
  - POMT1: Walker-Warburg; LGMD 2K
  - POMT2: Walker-Warburg
  - FKRP
    - MDC1C
    - LGMD2I
  - LARGE
    - Congenital muscular dystrophy MDC1D
    - myd mouse
  - DPM3: Myopathy + Cardiomyopathy
  - GNE: Hereditary inclusion body myopathy type 2 (HIBM 2; Nonaka)
- Also see: Metabolic disorders
Prevalence of recessive muscular dystrophies
- LGMD 2D: Most prevalent in US, Europe & Brazil
- LGMD 2C: Most prevalent in Tunisia
- Brazil has relatively high frequencies of LGMD 2E (8%) & 2F (6%)
- LGMD 2A: Common on Réunion Island, Guipuzcoa, Northern Indiana, Russia
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

LGMD 1: Dominant inheritance

LGMD 1A

l Myotilin (Titin immunoglobulin domain protein (TTID))

¹⁹; Chromosome 5q31; Dominant or Sporadic

Epidemiology
- > 15 families described
- Female = Male
- 10% of myofibrillar myopathies
Genetics
- Mutations
  - Missense; Lys36Glu; Ser55Phe; Thr57Ile; Ser60Cys; Ser60Ile; Gln74Lys; Ser95Ile; Ala115Thr
  - Most common in serine rich region of myotilin
- ~50% of families have no family history: Not related to specific mutation
- Similar locus to: Distal myopathy with vocal cord & pharyngeal weakness (VCPMD; MPD2))⁸
- 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 features⁴⁰
- 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
- Contractures: Ankles in some patients
- Progression: Slow; Late loss of ambulation (10 years)
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
l Myotilin ; Chromosome 5q31; Dominant
- Genetics: Missense; S39F in myotilin gene exon 2
- Indiana & Oregon families
- 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 -

LGMD 1B¹⁷

l Lamin A/C

; Chromosome 1q21.2; Dominant

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
- Mutations in same Lamin A/C gene produce many different clinical syndromes
  - Cardiomyopathy
    - Autosomal dominant dilated cardiomyopathy with A-V block (CMD1A): Rod domain
    - Atrial fibrillation: Early onset; Missense (E161K) mutation¹⁰
  - Myopathy
    - Emery-Dreifuss MD 2: Hydrophobic C-terminal region & Rod domain
    - LGMD 1B
    - Congenital muscular dystrophy with rigid spine
    - Quadriceps myopathy with dilated cardiomyopathy: Missense (R377H) mutation
  - Neuropathy: AR-CMT2A
  - Familial partial lipodystrophy (Köbberling-Dunnigan Syndrome): Globular C-terminal domain
  - Mandibuloacral dysplasia :
    - Mutation: R527H (C-terminal domain), Recessive
    - May be associated with partial lipodystrophy
  - Premature aging
    - Hutchinson�Gilford progeria : Recessive; Abnormal nuclear architecture
    - Werner�s syndrome, atypical : Dominant; More severe
  - Lethal phenotype: Homozygous LMNA nonsense mutation
- Mutation Database: HGMD
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: Mild myopathic changes
- 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
l Caveolin-3

; Chromosome 3p25; Dominant, Also Recessive

Caveolin protein LGMD 1C Clinical Genetics 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
    - Ala45Val: Rippling muscle disease
    - Ala45Thr
      - N-terminal domain
      - Disease associations: LGMD1C; Rippling muscle disease
      - Caveolin levels reduced > 90%
    - Ser52Gly
      - Domain with role in homo-oligomerization
      - Rippling muscle disease
    - Gly55Ser
      - Caveolin scaffolding domain
      - Inheritance: Recessive
      - Caveolin levels: Normal
    - Val57Met: HyperCKemia
    - 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>C⁶⁴
      - Homozygous
      - Intronic
      - Recessive inheritance
- External link: Leiden database
- Mutations in Caveolin-3 also cause
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)
  - 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 function: Required for myoblast fusion/myotoube formation
- Caveolin gene mutations & other MD: 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
LGMD 1C: Clinical features
- Onset
  - 5 years to Adulthood
  - 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
- Cramps: After exercise
- Variable clinical manifestations may occur in single family
Caveolin-3 mutations: Variant syndromes
- Recessive muscular dystrophy syndromes⁶⁴
  - 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 weakness
  - Isolated Hand & Foot muscle weakness: Arg26Gln mutation
- Hyper-CKemia⁶³
  - Mutations: Missense; Gly56Ser, Thr78Met
  - Frequency: 7% of Idiopathic Hyper-CKemia
  - Caveolin-3 staining of muscle: Normal
- Long QT syndrome⁶⁵
  - 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
- Pathology⁶⁶
  - 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
    - Reduced on muscle fiber sarcolemma & by Western blot
    - May be normal or high on small, regenerating muscle fibers
  - 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

LGMD 1D:

l Chromosome 7q; Dominant

Nosology: Confused terminology
- LGMD 1D: OMIM & HUGO
- LGMD 1E: Some authors³⁵
General: 2 families described
Clinical
- Onset: Mean 38 years
- Weakness: Proximal > Distal; Legs > Arms
- Dysphagia (20%)
- No associated systemic features
Laboratory
- Serum CK: Normal to 3x elevated
- Muscle pathology
  - Myopathic
  - Small muscle fibers rounded & angulated
  - Endomysial fibrosis

Familial Dilated Cardiomyopathy with Conduction Defect & Muscular Dystrophy (?LGMD 1E)

l Chromosome 6q23; Dominant

Nosology: Confused terminology
- LGMD 1E: OMIM & HUGO
- LGMD 1D: Some authors³⁵
1 Large family described: French-Canadian descent
Clinical
- Weakness
  - Onset: 2nd decade & later
  - Distribution: Proximal; Face normal
  - Calf hypertrophy: Occasional
  - 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
- Serum CK
  - Usually increased 2x to 4x control
  - More likely high in males than females

LGMD 1F³⁵

l Chromosome 7q32.1-32.2; Dominant

1 Large family described: Spanish
Onset
- Mean: 16 years
- Range: 1 to 58 years
- ? Anticipation
- Proximal leg weakness
Weakness
- Distribution
  - Proximal: Early in disease course;
  - Distal: Late; Extensor digitorum, Tibialis anterior, Toe extensors
  - Scapular winging: Some patients
  - Legs > Arms
  - Face: Normal in most; Some with earlier onset disease
  - Respiratory: Younger onset patients
  - Symmetric
  - Progression: Linear rate
    - More rapid in younger onset patients
    - Wheelchair in 2nd or 3rd decade in younger onset patients
- Muscle hypertrophy: Absent
- Contractures: Occasional late; Ankles
- Spinal deformity: Some younger onset patients
Laboratory
- Muscle pathology
  - Variable fiber size
  - Occasional degeneration
  - Increased connective tissue
  - Desmin: Mildly increased expression in some fibers
  - Rimmed vacuoles: Some patients
  - Ultrastructure: Autophagic vacuoles
- EMG: Myopathic
- Serum CK
  - Normal in 40%
  - Range: 47 to 2,920
- Cardiac: Normal EKG & Echocardiogram

LGMD 1G

l Chromosome 4q21; Dominant

Epidemiology: Brazilian-Caucasian family
Onset
- Age: 30 to 47 years
- Leg weakness
- Leg cramps
Clinical
- Homogeneous phenotype
- Weakness
  - Proximal
  - Legs 100%; Arms 90%
- Muscle atrophy
- Contractures: Limited flexion of fingers & toes
- Progression: Slow; 50% walking at 10 years after onset
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
  - Rimmed vacuoles: Stain with dystrophin & sarcoglycans
  - Small atrophic angulated fibers: Scattered groups

LGMD2: Recessive Inheritance

General
- Carriers: Have increased Serum CK in < 5% of cases
- Geographic foci
  - Brazil: LGD 2G
  - Manitoba Hutterites of Canada: LGD 2H
  - Denmark & England: LGD 2I
  - Finland: LGD 2J
  - French-Canadian: LGD 2L

LGMD 2A

l Calpain-3 (p94 protein)

; Chromosome 15q15.1-q21.1; Recessive

Genetics
Calpain-3 protein
Clinical
Laboratory

From: C Angelini MD

Genotype & Phenotype
- Mutations: > 150 identified⁷
  - 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 mutation⁵⁴
      - 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
  - Mutation Databases
    - HGMD
    - Leiden: Sequence variants
- Calpain-3 (p94) protein
  - Function
    - 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
    - Can bind & cleave titin
    - Role in cytoskeletal remodeling
    - 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
    - Subcellular: Nucleus ± Cytosol; Not membrane related
  - Halflife
    - Short (< 10 minutes)
    - Rapid turnover related to insertion sequences (IS) not present in other calpains
- 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
- 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 features²¹

LGD 2A: Erb phenotype

From: C Angelini
- 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
- Severity of weakness
  - Heterogeneous: Mild to Early onset severe
  - Mild phenotype in majority
  - Male = Female
- 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
- Weakness
  - General
    - Symmetrical
    - Proximal + Milder Distal
    - Legs > Arms at onset: Most patients
    - Progressive
  - Rectus abdominus
  - Peri-Scapular
    - Latissimus dorsi; Serratus magnus
    - Scapular winging (83%): Symmetric
  - Legs: Gluteus maximus; Adductors; Knee flexion; Ankle dorsiflexion
  - Arms: Shoulder adduction; Elbow flexion; Wrist extension
  - Respiratory
    - Vital capacity: Declines over time; Rarely < 80%
    - No nocturnal hypoventilation
  - Quadriceps: May be selectively spared
  - Normal: Face; Ocular & Bulbar
- Gait
  - Inability to walk on heels
  - Lumbar lordosis
  - Loss of walking: Mean late 2nd or 3rd decade
- 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
- CNS
  - Normal, or
  - Mild mental retardation: Average IQ = 77
- Cardiac: No involvement
- Some patients are asymptomatic with elevated serum CK levels
- 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 & Good function: 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
        Myopathic groups: May involve clusters or whole fascicles early in disease³⁴
      - 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
  - Dystrophy-related proteins
    - Calpain-3: Western blot patterns
      - Loss of all calpain-3 bands
        
        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 artefactual protein degradation
      - 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
  - Inflammation: Some biopsies with eosinophils
  - Ultrastructure: Patchy damage to myofibrillar Z, I & A bands
Diagnosis⁴¹
- 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
- Western blot
- Calpain-3 enzyme activity: Reduced
Mouse model: Calpain-3 knockout⁴²
- Misaligned A-bands
- Abnormal sarcomere formation

LGMD 2B

l Dysferlin

; Chromosome 2p13.3-p13.1; Recessive

Gene
Protein
Clinical
Laboratory
Pathology
Variant syndromes
Mouse models

From: C Angelini

Gene
- 55 exons
- Allelic with Miyoshi distal myopathy: Similar features
  - Onset age: Late childhood to early adult
  - Progression: Slow
  - Serum CK: Very high
- Locus near, but different from, Welander distal myopathy
Gene mutations²⁵
- > 300 different mutations described
  - 18% of patients with dysferlin deficiency have only 1 (heterozygous) mutation 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
    - G3370T: Mild disease phenotype; Later onset
    - G3510A: More severe disease; Earlier onset; High CK
    - Other common mutations: 3746delG; 4870delT
  - Sueca, Spain: Arg1905X⁵⁰
- Mutation Database
  - HGMD
  - Leiden: Sequence variants
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
- 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 to⁶²
  - 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
  - ? Role in membrane fusion or membrane repair
  - Ca⁺⁺-mediated muscle membrane
    - Homeostasis processes
    - Signal transduction events
- 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
Clinical: Mild phenotype

LGMD 2B
No calf hypertrophy
- Onset
  - Age
    - Mean 19 ± 3 years
    - Range
      - General: 10 to 39 years
      - Congenital onset 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 quadriceps, also psoas
    - Lower limb 9 years before upper limb
  - Arms: Especially biceps
  - Trunk: Glutei, Erector spinae, Shoulder girdle involved
  - Loss of ambulation > 30 years
  - 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 course⁶⁰
- Cramps & muscle discomfort: Some patients
- No cardiomyopathy
- 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
- CT: Gastrocnemius atrophy
- 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 mutations²²
      - 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 vesicles²³
  - Dysferlin tissue staining³⁰: Absent or Reduced
    - Absent staining more specific for LGMD 2B than reduced, but present, staining
    - Staining may be patchy among muscle fibers
    - Retained staining may be related to splice site mutations in dysferlin gene
    - No correlation between level of staining and clinical severity
  - Dysferlin Western blot
    - Common change in LGMD 2B: Dysferlin reduced to 0% to 15% of normal
    - Absent dysferlin on Western blot: Dysferlin gene mutations very common
    - Increased 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
- Distal myopathy
  - Miyoshi
  - Distal anterior dysferlinopathy
    - Onset: Foot drop; Steppage gait
    - Weakness
      - Legs
        
        Anterior: Ankle > Knee
        
        Distal > Proximal
      - Arms: Proximal
- Proximal + Distal
  - Onset: Proximal weakness; Calf atrophy
  - Weakness: More rapidly progressive
  - Muscle pathology: Inflammation more common
- 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
- Congenital onset⁷⁰
  - Weakness
    - Birth: Legs & Neck flexor
    - Walking at 19 to 21 months
  - Serum CK: Normal early; High after age 5
  - MRI: Pathology (STIR) in hamstring & gastrocnemius
  - Muscle: Dysferlin absent; α-dystroglycan normal
  - Mutation: p.Ala927LeufsX21 frameshift
- Carriers⁷⁴
  - 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 2C; Severe Childhood Autosomal Recessive (SCARMD)

l γ Sarcoglycan

; Chromosome 13q12; Recessive

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 mutation³⁶
  - 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 2D

l α-Sarcoglycan (Adhalin)

; Chromosome 17q21; Recessive

α-Sarcoglycan gene
- Promoters: 2
- Mutations
  - Most mutations are missense in extracellular domain of protein
  - Arg77Cys most common mutation, independent of ethnicity
  - Mutation Databases: HGMD; Leiden
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 phenotype³⁸
- Myalgias
- Scapular winging: 60%
- Calf hypertrophy: 15%
- Serum CK: Normal
- Muscle biopsy: Fiber-size variability; Atrophic fibers; Normal α-sarcoglycan by IHC

LGMD 2E

l β-Sarcoglycan

; Chromosome 4q12; Recessive

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 2F

l δ-Sarcoglycan

; Chromosome 5q33-34; Recessive

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
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
Clinical variant: Mild LGMD phenotype described
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

LGMD 2G

l Telethonin (Titin-Cap; TCAP)

; Chromosome 17q11-12; Recessive

Genetics
- Point mutations or small deletions
- Mutations produce stop codons
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
- Cellular localization: Sarcomeric Z-disc
Epidemiology: Brazil
Clinical features
- Onset: Mean age 12.5 years; Range 9 to 15 years
- Weakness:
  - Arms: Proximal
  - Legs: Proximal & Distal (Foot drop)
  - Face & Neck: Normal
  - Progression: 40% non-ambulatory in 3rd or 4th decade
- Muscle size
  - Calf hypertrophy 50%
  - Calf atrophy 50%
- Cardiac involvement 55%
Laboratory
- Serum CK
  - Increased 3- to 30-fold
  - Lower with greater age
- Muscle pathology
  - Myopathic: Degeneration & Regeneration
  - Rimmed vacuoles
  - Telethonin absent from muscle
Also see: Dilated cardiomyopathy 1N (DCM 1N)

LGMD 2H: Manitoba Hutterite Dystrophy

l Tripartite-motif containing gene 32 (TRIM32)

; Chromosome 9q31-q33; Recessive

Genetics: Mutations
- Homozygous for D487N point mutation: All patients
- Mutation localized in NHL domain
- 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: 8 to 27 years; Some asymptomatic in 3rd decade
- Onset: Proximal weakness; Back pain; Fatigue; Gait change
- Weakness
  - Proximal: Quadriceps & Pelvic girdle
  - Mild
- Progression: Slow; Ambulatory > 50 years of age
Laboratory
- Serum CK: High; 250 to 4,500 U/L
- EMG: Myopathic
Muscle biopsy: Mild dystrophic changes
- Fiber size variation
- Muscle fiber degeneration & regeneration
- Other: Fiber splitting; Internal nuclei
- Endomysial fibrosis

Sarcotubular myopathy⁴⁶
l 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 2I¹⁸

l Fukutin-related protein gene (FKRP)

; Chromosome 19q13.3; Recessive

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)
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
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
Clinical
- 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

l 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 2J

l Titin

; Chromosome 2q31; Recessive

Genetics
- Mutations
  - Homozygous for titin mutations
  - Mutation types
    - Missense: Leu293,356Pro (French)
    - 11 bp deletion (Finnish): Final exon (363)
- Allelic with
  - Finnish distal myopathy: Dominant inheritance
  - Dilated cardiomyopathy 1G: Dominant inheritance
  - Congenital myopathy + Fatal dilated cardiomyopathy : Recessive inheritance
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
- Wasting: Anterior tibial
- Progression
  - Usual: Wheelchair < 30 years, within 20 years of onset
  - Some patients ambulatory at 60 years
- No cardiomyopathy
Serum CK: High
Muscle biopsy
- Myopathic
- No vacuoles
- Loss of calpain-3
Mouse model: Homozygous knockout
- Severe: Lethal
- Weakness: Distal > Proximal

LGMD 2K : with Mental retardation and Reduced α-dystroglycan⁴⁵
l POMT1

; Chromosome 9q34.1; Recessive

Epidemiology: Turkish families
Genetics
- Mutation: Missense Ala200Pro; Homozygous
- Allelic with: Walker-Warburg syndrome
Onset
- Age: 1st decade
- Motor: Fatigue; Difficulty climbing stairs & running; Early milestones normal
Clinical
- Muscle
  - Size: Mild pseudohypertrophy
  - Weakness: Proximal
  - Course: Slow progression
- Joint contractures (50%): Ankles
- CNS: Mental retardation, IQ 50 to 76
Laboratory
- Serum CK: Very high (9x to 40x elevated)
- Muscle
  - Fiber size: Varied
  - α-Dystroglycan: Reduced glycosylation
- MRI: Normal CNS

LGMD 2L

⁶⁷
l Chromosome 11p13-p12; Recessive

Epidemiology
- French-Canadian families
- Intra-familial variability
Clinical
- Onset age: Mean = 33 years; Range 11 to 50 years
- Muscle atrophy: Quadriceps; Biceps brachii
- Asymmetric
- Face weakness: Few patients
- Muscle pain: 86%; 50% with, or after, exercise
- Calf hypertrophy: Some patients
- Contractures: Unusual
- Cardiac: Usually normal
Laboratory
- MRI: Early atrophy of medial quadriceps, hamstrings & adductor magnus
- Serum CK: Normal to 6000
- EMG: Myopathic; Some with spontaneous activity
Pathology: Muscle
- Fiber size: Varied
- Necrosis & Regeneration
- Internal nuclei
- Increased endomysial connective tissue
- Fiber splitting
- Inflammation: In severe case

LGMD 2M ⁵⁹
l Fukutin (FCMD)

; Chromosome 9q31; Recessive

Epidemiology: 5 families; Portuguese, Turkish, French, Israeli Jewish & Indian
Genetics
- Mutations
  - Types: Stop & Missense
  - 1167dupA; 1363delG; Arg47X; Ala170Glu; Arg246Gly; Arg307Gln; Tyr371Cys
- Allelic with
  - Fukuyama congenital muscular dystrophy
  - Cardiomyopathy
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

Myosclerosis ⁶⁹
l Collagen, type VI, subunit α2 (COL6A2)

; Chromosome 21q22.3; Recessive

Epidemiology: 1 family
Genetics
- Mutation: Q819X; Homozygous
- Allelic with
  - Bethlem myopathy
  - Ossification of posterior longitudinal ligament: Mutations in different part of COL6A1 gene
  - Ullrich congenital muscular dystrophy
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

Other Dominant Myopathies

Bethlem myopathy

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

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

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

; Chromosome 2q37; Dominant

Gene mutations: >10 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 with
  - Ullrich Scleroatonic muscular dystrophy: Same 3 COL6A subunit genes mutated
  - Myosclerosis: COL6A2 mutations
  - Ossification of posterior longitudinal ligament: Mutations in different part of COL6A1 gene
Protein: Collagen VI
- 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 mechanisms¹⁵
  - 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 sequences³¹
  - Vastus lateralis & hamstrings: Peripheral involvement, Central sparing³⁷
  - 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

Multiple epiphyseal dysplasia with mild myopathy¹³ (EDM3)

l Collagen, type IX, subunit α-3 (COL9A3)

; Chromosome 20q13.3; Dominant

Genetics
- Splice acceptor mutation in intron 2
- Causes skipping of exon 3
- Mutant collagen IX is poorly cross-linked
Type IX collagen proteins
- 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
- Function: Organization & spacing of type II collagen fibrils
- Modifications: NC3 domain of 2(IX) chain can be modified by a single glycosaminoglycan
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
- Joints
  - Early onset degenerative disease
  - Especially knees: knee 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: Epiphyseal changes
- Muscle biopsy
  - Mild myopathic changes with variability in fiber size
  - Perimysial collagen: Normal
  - Immunostaining: Normal dystrophin, merosin & sarcoglycans
- Epiphyseal chondrocytes: Intracytoplasmic inclusions

Dominant Myopathy with Bone Fragility

⁵¹
l Chromosome 9p21-p22; Dominant

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

Dominant Myopathy with Cardiomyopathy¹
l 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 CK¹⁰
l 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
l Dok-7 (C4ORF25)

; Chromosome 4; Recessive

Myopathy with Dilated Cardiomyopathy⁷⁵
l Dolichyl-phosphate mannosyltransferase 3 (DPM3)

; Chromosome 1q12-q21; Recessive

Epidemiology: Single Greek patient
Genetics
- Mutation: Leu85Ser; 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 years
  - Weakness: Proximal
  - Waddling gait
- Weakness
  - Proximal
  - Progression: Slow
- Pseudohypertrophy: Gastrocnemius
- Tendon reflexes: Reduced
- Contractures: Ankle
- Cardiomyopathy
  - Dilated
  - Stroke-like episodes
- Short stature
- CNS & Eye: Normal
Laboratory
- Serum CK: 1500 to 3000
- CDG type I: Defective N-glycosylation in Endoplasmic reticulum
  - Increased ratio of mono- versus diglycosylated transferrin
  - Partial absence of complete biantennary N-glycans
- Muscle: Myopathic
  - Fiber-size variation
  - Internal nuclei
  - Necrosis fibers
  - Rimmed vacuoles,
  - Fiber splitting
  - Endomysial fibrosis
  - α-Dystroglycan: Reduced

Myopathy with Lipodystrophy⁷⁶
l Polymerase I and transcript release factor (PTRF; Cavin-1; FKSG13)

; Chromosome 17q21.31; Recessive

Epidemiology: 5 unrelated Japanese
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
- LipodystrophyL Loss of adipose tissue in several regions including face
- Weakness
  - Mild
  - Distal dominant or Generalized
- Muscle hypertrophy
- Muscle mounding: Electrically silent
- Other systems
  - Hepatosplenomegaly
  - Acromegaloid features
  - Umbilical prominence
- Some patients
  - Myaslgias
  - Cardiac arrhythmia
  - Transient immunodeficiency (IgA)
  - Recurrent pneumonia
  - Constipation
  - Chalasia
  - Skeletal: Lordosis or Scoliosis
- 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

LGMD 4

l 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 myopathy⁵⁶
l 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 myopathy⁵⁷
l 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 involvement⁵⁸
l 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

X-linked myopathies

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

X-linked Myopathy with Excessive Autophagy^5,16

l VMA21 (ATP6V0E1)

; Chromosome Xq28; Recessive

Epidemiology: Families in Europe & North America, ~14
Genetics: Mutations⁷¹
- Single nucleotide substitutions
- Locations: Intron; Splice site; 3' UTR
- Mutation effects: Reduced VMA21 abundance
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: Upregulated
  - Proliferation of large & ineffective autolysosomes
    - Engulf sections of cytoplasm, merge & form vacuoles
Clinical: Similar patterns among families
- Onset age
  - Age: Range Neonatal to 20 years; Typical 5 to 10 years
  - Weakness: Difficulty climbing stairs & running
- Weakness: Limb-Girdle; Mild
  - Proximal
  - Symmetric
  - Legs > Arms
  - Distal: Ankles
- No muscle hypertrophy or clinical myotonia
- Progression
  - Very slow or Stable
  - Longevity not altered
  - Many patients in wheelchair in 6th decade
- Cardiac: Normal
- CNS: Intellect normal
- 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
    - Excessive autophagic activity
    - Location: Sarcoplasm; Internal or Near surface
    - Basophilic granules
    - Contents
      - Lysosomal enzymes
      - Calcium
      - C5b-9 complement components
      - Cellular debris
    - Immunostaining
      - Dystrophin: Vacuolar membrane staining
      - LAMP-2 & Sarcoglycan
      - α1-Antitrypsin: Within vacuoles
    - Acid phosphatase: Variably present
    - Vacuolated fibers express polysialylated isoform of NCAM
    - Differential diagnosis
  - Exocytosis of the phagocytosed material
- 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)

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

; Chromosome Xq24; Dominant, more severe in males

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
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
Clinical²⁹
- 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%
- 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
Carrier females
- Frequency: > 70% of carriers; All eventually have abnormal EKG
- Onset
  - Age: 12 to 53 years
  - Cardiac signs
- Weakness: 33%; Proximal limb & Neck
- Cardiomyopathy: Dilated > Hypertrophic
- Some with death in 4th & 5th decade; Pacemaker in 17%
- Retinopathy
  - Pigmentary changes: Peripheral
  - Electroretinogram: Abnormal
  - Visual fields: May be abnormal central region
- Serum CK: 76 to 643
- Treatment: Cardiac transplantation or Pacemaker
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
- 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 retardation⁵⁵
- 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
Danon syndrome: Variant
- Scapuloperoneal muscular dystrophy with mental retardation & lethal cardiomyopathy

Myofibrillar (Desmin -storage) Myopathies^3,11

Clinical features
Pathological features
Hereditary types
αB-crystallin: 11q22
Cap: TPM2; 9p13
Congenital with desmin inclusions: SEPN1; 1p36
Desmin: 2q35
Filamin C: 7q32
LGMD 1A: Myotilin; 5q31
ZASP: 10q22
Myopathy + Right ventricular cardiomyopathy: 10q22
Congenital MD + JEB: Plectin; 8q24
BAG3: 10q25
Proximal & Respiratory muscle weakness
Type 1: 2q24
Type 2: 2q21
Restrictive cardiomyopathy
Scapuloperoneal muscular dystrophy: FHL-1; Xq26

Desmin knock-out mouse

Also see
Inclusion body myositis
Intermediate filament disorders

From: HPRD

Desmin

Myofibrillar myopathies: General

Clinical features
- Weakness
  - Proximal & Distal
  - May present with respiratory failure
- Cardiomyopathy (50%)
- EMG: Myopathy ± Denervation changes
- Serum CK: Normal, or Elevated < 5x
Pathological features
- 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 : Desmin

mutations
l 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: Kaeser scapuloperoneal syndrome
Desmin protein features⁴³

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
Clinical features
- General
  - Syndromes may involve skeletal muscle, heart or both
  - Smooth muscle involved in some syndromes
  - Inter- and intra-familial variability with same mutation
  - Patterns of weakness
    - Scapuloperoneal
    - Limb-Girdle
    - Distal
    - Distal + Proximal
- Heterozygous:
  - Mutations: Ala337Pro; Leu345Pro; L370P
  - Inheritance: Dominant
  - Mechanism: ? Dominant negative effect on filament formation
  - Clinical
    - Skeletal myopathy
      - Onset: 20's & 30's
      - Early: Distal progressing to Proximal weakness
      - 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
  - Also see: R350P (Kaeser scapuloperoneal syndrome)
Recessive variants
- Compound heterozygosity (Type 3): Ala360Pro & Asn393Ile
  - Recessive: Heterozygote carriers not involved
  - 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
- Homozygous in-frame deletion⁷³
  - Mutation: p.R173_E179del
  - Mutated protein
    - No assembly of desmin filaments
    - Reduced ability to form intermediate filament network
  - Onset
    - Age: 6 months
    - Syncope
  - Clinical
    - 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
Cardiomyopathy: Desmin
- 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: αB-crystallin

(Type 1)³⁹
l αB-crystallin (CRYAB)

; Chromosome 11q22.3-q23.1

Genetic: Autosomal dominant
- Mutations: Myopathy
  - Missense: Arg120Gly
  - Truncating: C-terminal; 464delCT & Gln151X
- Other mutations in same gene (1-BP Del, 450A) cause: Dominant Congenital Posterior Polar Cataract
Protein

From HPRD
αB-crystallin
- Type: Heat shock protein 20 (HSP20) family
- Location
  - Tissues: Muscle; Lens; Myocardium; Kidney epithelium
  - Subcellular: Cytosol
- Functions
  - Chaperone
  - Lens: Forms aggregates with αA-crystallin; Maintains lens transparency
- 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
- Onset: Early to middle adulthood
- Progression: Slow; Sudden cardiac death
- Weakness
  - Proximal: Most patients
  - Distal: Legs; Some patients
  - Cranial nerve: Face, Bulbar (velopharyngeal)
  - Respiratory: 1 patient
- Chest pain
- Cardiac: Arrhythmia, conduction block, congestive failure
- Other systems: Lens opacities; 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
  - Subsarcolemmal & intermyofibrillar
  - Contain phosphorylated desmin
  - Molecular components: Desmin, aB-crystallin, 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

Myofibrillar myopathy with ZASP mutations⁴⁴

l ZASP (LDB3)

; Chromosome 10q22.3-q23.2; 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 with
  - Markesbery distal myopathy
  - Dilated cardiomyopathy ± Isolated non-compaction of left ventricular myocardium
- Locus near: Myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy
- ~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
Onset
- Age: 44 to 73 years
- Weakness: Most common early feature
Clinical
- Weakness: May be proximal or distal
  - Proximal > Distal (45%)
  - Proximal + Distal (27%)
  - Distal only (9%)
  - Proximal only (18%)
  - Selective scapular: 1 patient
  - Respiratory: Not prominent
- Cardiac (27%)
- Polyneuropathy (45%)
Laboratory
- Serum CK: Normal to 6x elevated
- EMG: Myopathic; Irritable (Fibrillations & Myotonic discharges)
Muscle pathology: Myofibrillar myopathy
- 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: Strong staining for myotilin, desmin, αB-crystallin, dystrophin & NCAM
- Ultrastructure: Z-disk streaming & disintegration; Disorganized sarcomeres & myofibrils
Mouse variant: ZASP deletion (Cypher or Oracle)
- Causes skeletal & cardiac myopathy with fragmented Z-disks

Myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy (ARVD7)¹⁴

l Dominant; Chromosome 10q22.3

Epidemiology: Swedish family
Similar locus to: ZASP myopathy
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 cardiomyopathy²⁸
l 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

l 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)
l Autosomal Dominant

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

Congenital muscular dystrophy with desmin inclusions

l 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 myopathy⁴⁷

l Filamin C (Filamin 2; FLNC)

; Chromosome 7q32.1; Dominant

Epidemiology: German family
Genetics: Truncation mutation
- Mutation: W2710X
- Truncated protein: Abnormal folding; Unable to dimerize properly
Filamin C protein
Clinical

Onset
- Age: 37 to 57 years
- Weakness: Usually proximal
- Back pain
Weakness
- Legs > Arms
- Usually proximal > distal
- 1 patient with selective calf weakness
- Respiratory: 50%
Polyneuropathy: 40%
Cardiac: 1 patient; Bundle branch block; Reduced ejection fraction

Laboratory
- Serum CK: Mildly elevated, 2x to 8x
- Muscle pathology: Myofibrillar myopathy
  - Internal nuclei
  - Fiber splitting
  - Necrosis: Isolated fibers
  - Gomori trichrome stain: Hyaline masses; Vacuoles
  - Cytoplasmic aggregates: Contain filamin C, desmin, myotilin, dystrophin, sarcoglycans

Myofibrillar myopathy

⁶⁸
l BCL2-associated athanogene 3 (BAG3)

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

Epidemiology: 1 family
Genetics (Mutation): Pro209Leu
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
- Skeletal
  - Rigid spine
  - Scoliosis
  - Contractures
- Polyneuropathy (1 patient): Axonal & Demyelinating
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

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) myopathy¹²
- Emetine: Painful myopathy ± Rhabdomyolysis

Intermediate filaments & Disorders²⁰

General features of intermediate filaments
- 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
- Mutations: Often disrupt aggregation of intermediate filament proteins
- Neurofilaments
  - Major IF in neurons: Up to 85% of protein content
  - Composed of 3 subunits
    - NF light chain (68 kDa): Forms backbone & initiates assembly of NF
    - NF medium chain (160kDa)
    - NF heavy chain (200 kDa)
  - Structure: Carboxy terminals of NFH & NFM form side arm projections
    - Allow interactions among neurofilaments
    - Underlie the "cross links" between adjacent filaments
  - IF association molecules
    - Plectin; BPAG1
    - Mediate the cross-linking of NF & microtubules
    - Produce the cytoskeletal lattice
  - Phosphorylation
    - Location
      - 40 to 70 Lys-Ser-Pro (KSP) repeats
      - C-terminus domains
    - Probable roles
      - NF assembly
      - NF transport from perikaryon to the axon through slow transport mechanisms
      - NF incorporation into a cytoskeletal network
  - NF function: Determine axonal caliber & conduction velocity
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
- Desmuslin : Muscle; Co-localizes with desmin
- Filensin : Lens; Cataracts
- 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
  - ALS, Sporadic & Familial NF-H tail deletions
  - CMT 2E: NF-L
  - Immune Polyneuropathy: Anti-NF Antibodies
  - Toxic polyneuropathy: β,β-Iminodipropionitrile; 2,5-Hexaneidone (Glue-sniffing); DMAPN
- 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
- Vimentin : Mesenchyme; Null mutation has no phenotype
Myofibrillar myopathies: Molecular basis not defined

Myopathy + Right ventricular cardiomyopathy (10q22)
Proximal & Respiratory muscle weakness (2q24)
Scapuloperoneal muscular dystrophy (12q13)

Intermediate filament-associated proteins & mutations
- αB-crystallin (11q22): Dominant myopathy
- Bullous pemphigoid antigen 1
- Desmoplakin : Keratosis palmoplantaris striata II; Dilated cardiomyopathy
- Emerin: Emery-Dreifuss muscular dystrophy
- Gigaxonin: Giant axonal neuropathy
- Plectin: Congenital Muscular Dystrophy with Familial Junctional Epidermolysis Bullosa
Neurofilament accumulations in neuropathy
- 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
External link: Cytoskeleton

CYTOPLASMIC BODY MYOPATHIES (also see Distal myopathies)

Severe limb-girdle: ? Recessive
Mild limb-girdle: Dominant
Proximal & Respiratory weakness (Type 1): 2q24-q31; Dominant
Proximal & Respiratory weakness (Type 2): 2q21; Dominant
Distal: Dominant
Plectin deficiency

Pathology
Cytoplasmic body myopathies
Denervation

Severe limb-girdle type
l ? Recessive
- Clinical features
  - Onset: Infancy or childhood
  - Hypotonia & proximal weakness; Skeletal abnormalities
  - Respiratory insufficiency
  - Death: Early adulthood
Mild limb-girdle type
l Autosomal Dominant
- Clinical features
  - Onset: Adolescence
  - Slowly or non-progressive limb-girdle weakness
Myopathy with Proximal Weakness and Early Respiratory Muscle Involvement (Type 1)⁶
l Chromosome 2q24-q31; Dominant
- Locus similar to tibial muscular dystrophy
- Epidemiology: Swedish families
- Clinical
  - Onset: Adult; 2nd to 5th decades; Average ~35 years
  - Weakness
    - Proximal: Upper & lower extremities
    - Respiratory: Diaphragm; Early
    - Neck flexors
    - Other occasional: Foot extensor
- Laboratory
  - Serum CK: Normal or slightly elevated
  - Pathology
    - Cytoplasmic bodies containing actin in type I muscle fibers
    - Ultrastructure: Thin filaments & Dense material related to Z-discs.
Myopathy with Proximal Weakness and Early Respiratory Muscle Involvement (Type 2)⁹
l 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.
Distal type
l Autosomal Dominant
- 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
  - Pathology: Myofibrillary inclusions in cytoplasm of Type I muscle fibers
Pathology
- Aggregates of Z-disk filaments
- Histochemical properties
  - Stain strongly with Gomori trichrome & Myoadenylate deaminase
  - Stain poorly with myofibrillary ATPase & NADH
  - Type I fibers in distal type; Type I or II fibers in limb-girdle syndromes
  - PAS +
  - Contain actin ± desmin, dystrophin, β-amyloid precursor, N-CAM
- Ultrastructure
  - Foci of myofibrillary destruction: Z-disk derived bodies & streaming
  - Cytoplasmic or spheroid bodies: Thick & thin filament remnants

MYOPATHIES WITH TUBULAR AGGREGATES

General features
- Serum CK: Normal or Mildly high
- Muscle pathology⁴⁹
  - Cytoplasmic aggregates of membranous tubules
  - Histochemical staining
    - Positive: NADH-TR (blue); Gomori trichrome (Red); AMPDA; Esterase
    - Negative: SDH
  - Most often, but not always exclusively, in type II fibers
  - Derived from: Sarcoplasmic reticulum (Dilated terminal cisternae)
  - Ultrastructure: Aggregates of 50 to 70 nm tubules, Enclose smaller tubule or flocculent material
  - Protein constituents
    - Common: Calsequestrin; SR Ca⁺⁺ ATPase; Dihydropyridine receptor (DHPR); Heat shock proteins; Dysferlin; Tau; Ubiquitin; Emerin (Rare)
    - Not present: Dystrophin; Sarcoglycans; Desmin
Proximal myopathy syndromes
l Autosomal Dominant (or recessive)
- Weakness
  - Proximal
  - Onset: Childhood or early adult
  - Slowly progressive
- Other: Some families with EOM weakness, ankle contractures
- Serum CK: Normal or Mildly high
l Autosomal Dominant²⁴
- 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
l Sporadic
- Onset: Teens
- Weakness: Proximal
- Progression: Slow
- Serum CK: Normal or Mildly high
- Pathology: Tubular aggregates in Type I & II muscle fibers
Familial Limb Girdle Myasthenia
l Autosomal Recessive
- Onset: Childhood or Adult
- Clinical features
  - Fatigability
  - Proximal Weakness
  - Childhood onset
  - Some with cardiomyopathy
- Laboratory
  - Serum CK: Normal
  - EMG: Myopathic
- Treatment: Some response to anti-cholinesterase
- Other congenital MG with tubular aggregates: Slow channel syndrome
Exercise induced muscle pain & stiffness
l Sporadic or Dominant
- Male > Female
- Onset: Childhood or Adult
- Discomfort
  - Muscle pain: Aching & Stiffness
  - Cramps
  - Increased by exercise: may last up to 36 hours
  - Legs > Arms
- Weakness: Minimal or None
- Serum CK: Mildly high, especially after exercise
- EMG: Normal or Myopathic
Periodic paralysis: Hypokalemic
Ornithine aminotransferase deficiency ⁶¹
l Chromosome 10q26; Recessive
- Epidemiology: Common in Finnish families
- 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
- Myotonia congenita
- Malignant hyperthermia
- Myositis
- Alcoholic myopathy
- Whipples disease
- Porphyria cutanea tarda
- Phosphoglycerate mutase M deficiency: Atypical ultrastructure
Mouse models
- MRL +/+ males: Tubular aggregates
  - Number & size increases with age
  - Castration prevents formation
- Creatine kinase knockout mice

Myopathy with tubular arrays⁴⁸

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

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

LIMB-GIRDLE MUSCULAR DYSTROPHY (LGMD) SYNDROMES2