• 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

• 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 (Myofibrillar myopathy 3 (MFM3) )

• 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
  • Muscle fiber degeneration
  • Muscle fiber size: Varied
  • Fiber splitting
  • Central nuclei
  • Z-line streaming
  • 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 -

• Genetics
  • Lamin A/C gene mutation types
    • Missense & Deletion of codon in rod domain
    • Splice donor site: Protein lacking half of the globular tail domain
  • Lamin A/C gene mutations: Other clinical syndomes
  • Mutation Database: HGMD
• Lamin A/C protein
• Clinical
  • Onset: < 20 years
  • Weakness
    • Common: Symmetric; Proximal; Lower limb
    • Variant: Quadriceps with Arg377His mutation
  • Progression: Slow; Upper limbs involved by 3rd or 4th decade
  • No contractures
  • Associated systemic feature: Cardiomyopathy (62%)
    • A-V conduction block
    • Occasional dilated cardiomyopathy: Onset before weakness with Arg377His mutation
• Laboratory features
  • Serum CK: Normal to mildly elevated
  • Muscle: 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

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

• Genetics
  • Caveolin-3 gene mutations
    • General: Most commonly located in scaffolding domain of protein
    • Specific mutations
      • Arg26Gln
        • Caveolin levels reduced 60% to 80%
        • Disease associations
          • Idiopathic hyperCKemia
          • Rippling muscle disease
          • Distal myopathy
      • Asp27Glu
        • Rippling muscle disease ± Weakness (Distal or Proximal)
        • Variable clinical features in family
      • Pro28Thr
        • Onset 35 years
        • Rippling muscle disease
        • Fatigue: Exercise induced muscle pain, Cramps
        • Serum CK: 1100
      • Ala45Val: Rippling muscle disease
      • Ala45Thr
        • N-terminal domain
        • Disease associations: LGMD1C; Rippling muscle disease
        • Caveolin levels reduced > 90%
      • A46V: Cardiomyopathy with Rippling muscles
      • Ser52Gly
        • Domain with role in homo-oligomerization
        • Rippling muscle disease
      • Gly55Ser
        • Caveolin scaffolding domain
        • Inheritance: Recessive
        • Caveolin levels: Normal
      • Val57Met: HyperCKemia
      • T63S: Cardiomyopathy
      • Cys71Trp: ? Disease association
        • Caveolin scaffolding domain
        • Caveolin levels: Normal
      • Homozygous: L86P or A92T
        • Rippling muscle disease: Severe, Recessive
      • Pro104 Leu
        • Missense mutation in membrane-spanning region
        • Disease associations: LGMD1C; Rippling muscle disease
        • Caveolin levels reduced > 90%
      • Arg125His: ? Disease association
        • C-terminal domain
        • Caveolin levels normal
      • 186Del9
        • Microdeletion in the scaffolding domain
        • Caveolin levels reduced > 90%
      • Splicing: IVS1+2T>C⁶⁴
        • Homozygous
        • Intronic
        • Recessive inheritance
  • External link: Leiden database
  • Mutations in Caveolin-3 also cause
    • Rippling muscle disease: Dominant or Recessive
    • Increased CK with normal strength
    • Distal myopathy
    • Cardiomyopathy, familial hypertrophic
    • Long QT syndrome 9
• 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 functions
      • Required for myoblast fusion/myotoube formation
      • Regulates myostatin signalling: Suppresses activation of type I myostatin receptor
  • 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 myopathy (MPDT)
    • Nosology: Tatayama myopathy
    • Genetics: Arg26Gln; N33K mutations
    • Clinical
      • Weakness
        • Onset age: 3rd to 5th decade
        • Isolated Hand & Foot muscles
        • Neck flexors: Mild
      • Rippling: Present in some patients
    • Laboratory
      • Serum CK: High
      • Muscle
        • Internal nuclei
        • Type I predominance
        • Caveolin-3 nearly absent
  • Hyper-CKemia⁶³
    • Mutations: Missense; Gly56Ser, Thr78Met
    • Frequency: 7% of Idiopathic Hyper-CKemia
    • Caveolin-3 staining of muscle: Normal
  • Cardiomyopathy: Varied types
    • Hypertrophic
    • Dilated
    • 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
      • LGMD1C
        • Reduced on muscle fiber sarcolemma & by Western blot
        • May be normal or high on small, regenerating muscle fibers
      • Reduced on sarcolemma in other hereditary disorders
        • VCP myopathy (IBMPFTD)
        • Cavin-1
    • Dysferlin
      • Reduced on muscle fiber sarcolemma
      • Normal by Western blot
    • Ultrastructure: Reduction in caveolae; Loss of myofibrils.
• Caveolin disorders: Mouse models
  • Overexpression of wild type caveolin-3
    • Myopathy
    • Reduced dystrophin
  • Overexpression of Pro104Leu mutant caveolin-3
    • Down regulation of wild type caveolin-3
    • Myopathy: Severe
  • Caveolin-null
    • T-tubule abnormalities
      • Mislocalized dihydropyridine receptor-1α & ryanodine receptor
      • Iregular orientation of T-tubules
    • Loss of caveolae at sarcolemmal membrane
    • Muscle fiber degeneration: Especially in soleus & diaphragm
    • No effect on dystrophin complex
• Links: Leiden

• Nosology: Confused terminology
  • LGMD 1D: HUGO
  • LGMD 1E: OMIM & Some authors ³⁵
• Epidemiology
  • DNAJB6 mutations in 5 families
  • US & Europe
• Mutations
  • Missense
  • Phe89Ile; Phe93Leu; Pro96Arg
  • Location: G/F domain
• DNAJB6 protein
  • HSP40/DNAJ family
  • Protects client proteins from irreversible aggregation
  • Expressed in muscle & other tissues
  • Interacts with BAG3
  • See: Other chaperone-related protein disorders
• Clinical
  • Onset: Mean 38 years; 3rd to 6th decade; 28 to 50 years
  • Weakness
    • Distribution: Variable
      • Proximal > Distal or Distal > Proximal
      • Legs > Arms
      • Hamstring > Quadriceps: Some patients
    • Progression: Slow; Wheelchair after 20 to 30 years
  • Dysphagia (20%)
  • No associated systemic features
• Laboratory
  • Serum CK: Normal to 5x elevated
  • EMG: Myopathic; Some with irritability
  • Muscle pathology
    • Myopathic
    • Small muscle fibers: Rounded & Angulated
    • Endomysial fibrosis
    • Rimmed vacuoles
    • Eosinophilic cytoplasmic bodies
    • Aggregates: Contain SMI-31, TDP-43 & DNAJB6
    • Small fibers express neonatal & fetal myosin

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

• Epidemiology 1 Spanish family
• Genetics
  • Mutation: c.2771del
• TNPO3 protein
  • Location: Nuclear
  • Transport of serine/arginine rich proteins into nucleus
  • HIV-import into nucleus
• Onset
  • Mean: 16 years
  • Range: 1 to 58 years
  • 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
    • Nuclei: Abnormal morphology
    • Rimmed vacuoles: Some patients
    • Ultrastructure: Autophagic vacuoles
  • EMG: Myopathic or Neurogenic
  • Serum CK
    • Normal in 40%
    • Range: 47 to 2,920
  • Cardiac: Normal EKG & Echocardiogram

• 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

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

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

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
          • Eosinophils in some assciated cellularity
          • 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
    • Inflammation
      • Some biopsies
      • May be perivascular or endomysial
    • 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
    • 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

Gene Protein Clinical Laboratory Pathology Variant syndromes Mouse models

From: C Angelini

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

  LGMD 2B No calf hypertrophy

  • Onset
    • Age
      • Mean 19 to 27 years
      • Range
        • General: 10 to 39 years
        • Congenital & 8th decade onsets reported
      • Heterogeneity in single family may occur
    • Leg weakness
      • Proximal
      • May be associated with period of exercise
  • Weakness
    • Mild
    • Asymmetry: Common
    • Legs
      • Distal: Posterior muscles
        • Especially gastrocnemius
        • Early inability to walk on toes
        • Differential diagnosis: Distal myopathy with anterior leg sparing
      • Proximal
        • Anterior & Posterior muscle groups
        • Especially quadriceps, also psoas
      • Lower limbs involved 9 years before upper limbs
    • Arms
      • Especially biceps
      • Deltoid: Often spared
    • Trunk: Glutei, Erector spinae, Shoulder girdle involved
    • Face: Generally normal
    • Loss of ambulation: > 30 years
    • Respiratory: More with longer disease duration; Overall 50% have VC < 80%
    • Wide inter- and intrafamilial variation
    • Progression: Slow; Most walk until > 33 years, some into 6th decade
  • Calf size
    • Hypertrophy: Some patients
      • Deltoid hypertrophy with biceps atrophy
      • Posterior leg (Calf): May be early in disease course
    • Occasional distal onset patients
      • Subacute, painful enlarged calves early in course⁶⁰
  • Cramps & muscle discomfort: Some patients
  • No cardiomyopathy: Clinically preserved; EF generally > 50%
  • Same mutations may also produce Miyoshi distal myopathy
    • ? Modifier genes determine phenotype
• Laboratory features
  • CK
    • Typical
      • Very high
      • Range: 10x to 72x normal; Up to 27,000
      • Lowest: Normal
    • Presymptomatic: 343 to 3,000
    • ? Age-dependent increase
  • EMG: Myopathic
    • Motor units: Small amplitude; Short duration
    • No spontaneous activity
  • Imaging
    • Early involvement on MRI or CT
      • Posterior leg: Gastrocnemius atrophy, especially medial heads; soleus
      • Thigh: Hamstrings
      • Erector spinae
    • Late or minimal involvement: Gracilis; Sartorius; Glutei
  • Muscle
    

    Dysferlin staining in normal muscle

    • Pathology: Dystrophic Muscle
      • Necrosis & degeneration of muscle fibers
      • Endomysial connective tissue: Increased in more involved muscles
      • Muscle fibers: Size variation, may appear bimodal; Splitting
      • No vacuoles
      • Inflammation: Some 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
      • Reduced dysferlin staining: Not specific for dysferlinopathy; 60% with no mutation
    • Dysferlin Western blot
      • Common & specific change in LGMD 2B: Dysferlin reduced to 0% to 20% of normal
      • Absent dysferlin on Western blot: Dysferlin gene mutations very common
      • Good correlation between skeletal muscle (234 kDa) & monocytes (doublet 224 to 234 kDa) using WB
      • 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
  • General
    • Late in disease course: Varying weakness phenotypes merge
  • Distal myopathy: Miyoshi
  • Distal myopathy: Distal anterior dysferlinopathy (DMAT;DACM)
    • Onset: Foot drop; Steppage gait
    • Weakness
      • Legs
        • Anterior: Ankle > Knee
        • Distal > Proximal
      • Arms: Proximal
  • Proximal + Distal myopathy
    • Onset: Proximal weakness; Calf atrophy
    • Weakness: More rapidly progressive
    • Muscle pathology: Inflammation more common
  • Later onset, Proximal, Arms > Legs ⁸⁵
    • Mutation: Trp999Cys; Homozygous
    • Onset
      • Age: Mean 38 years; 16 years later than others average
      • Arm symptoms
    • Weakness: Proximal
    • Serum CK: High but lower than average
  • Pain syndrome
    • Onset: Distal leg (calf) painful swelling without weakness or atrophy
      • Unilateral or Bilateral
    • No weakness or atrophy
  • Asymptomatic with elevated serum CK levels
    • Frequency: 5% of dysferlinopathies
    • Mutations: Missense or Stop
    • Age: 28 & 50 years
    • MRI: Mild gastrocnemius pathology
  • Congenital onset ⁷⁰
    • 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
  • Carriers ⁷⁴
    • May be symptomatic
    • Mutations: G519R; D625Y
    • Clinical
      • Weakness: Legs; Proximal or Distal; Progressive
      • Calf myalgias: 1 patient
    • Serum CK: High; 600 to 3000
    • Muscle
      • Myopathy
      • Dysferlin expression: Reduced & Patchy
• Mouse model: SJL
  • Mutation
    • Genomic: 141 bp intronic deletion involving tandem repeat
    • Effects of mutation
      • Alters 3' splicing site
      • Causes deletion of exon 45 in cDNA: 171-bp in-frame deletion
    • Protein results
      • Deletion of 57 amino acids
      • Reduced amount to 15% of normal
  • Pathology: Myopathy ± Inflammation
• Mouse model: A/J
  • Retrotransposon insertion in intron 4 (5' end) of dysferlin gene
  • Progressive myopathy: Proximal > Distal
  • Perivascular inflammation
  • Dysferlin: Absent by Western blot

• 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

• 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

• 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

• δ-Sarcoglycan gene
  • Promoters: 3; 1 predominantly in skeletal muscle
  • Mutations
    • Frameshift ® Premature truncation of protein: del656C: African-Brazilian ancestry
    • Missense: Glu262Lys (Near cysteine-rich region)
    • Nonsense ® Premature truncation of protein: E93Ter; Arg165Ter; Trp30Ter
    • Databases: HGMD; Leiden
  • Allelic with: Dilated cardiomyopathy 1L (CMD 1L)
• 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

• Epidemiology: Brazil (Italian ancestry) & Europe
• Genetics
  • Point mutations or small deletions
  • Mutations produce stop codons
  • Trp25X; Gln35X; g.637-640del2
• 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
• 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%
  • Cramps: Occasional patient
  • Cardiac involvement 55%
• Laboratory
  • Serum CK
    • Increased 3- to 30-fold
    • Lower with greater age
  • Muscle imaging
    • Preservation: Adductor longus
    • Hypertrophy: Sartorius
    • More involvement: Quadriceps; Anterior tibial
  • Muscle pathology
    • Myopathic: Degeneration & Regeneration
    • Rimmed vacuoles: Some patients
    • Lobulated muscle fibers
    • Telethonin absent from muscle
• Variant telethonin syndrome: Dilated cardiomyopathy 1N (DCM 1N)
• Variant telethonin syndrome: Congenital Muscular Dystrophy ⁸⁰
  • Epidemiology: French male
  • Mutation: Homozygous Gln58X
  • Clinical
    • Motor
      • Milestones: Delayed head control & sitting
      • Weakness
        • Proximal (Psoas; Adductors) > Distal
        • Anterior tibial
        • Neck flexion
        • Course: Minimal progression
      • Gait: Waddling; Falling
      • Muscle size: Glutei wasting; Calf hypertrophy, mild
    • Skeletal
      • Scapular winging
      • Scoliosis
      • Joint laxity: Distal arms
      • Contractures: Ankles
    • Heart: Normal
  • Laboratory
    • Pathology: Muscle
      • Fiber size: Varied
      • Internal nuclei
      • Necrosis & Regeneration: Some clusters
      • Type I fibers: Small
      • Telethonin: Absent
      • α-Dystroglycan: Normal
    • Serum CK: 600 to 1300

• 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

• 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

• Nosology: Muscular dystrophy-Dystroglycanopathy
• Epidemiology
  • > 40 familes
  • Carrier risk: ~ 1:400
  • Common in Denmark & parts of England
• Genetics
  • Point mutations most common: Missense
  • Common mutation in 1 allele (> 90%): Leu276Ileu (C826A)
  • Disease severity correlates with mutation in 2nd allele
  • Leu276Ileu homozygosity correlates with less severe phenotype
  • Allelic with
    • Congenital muscular dystrophy with muscle hypertrophy & Normal CNS (MDC1C)
    • Myopathy with abnormal merosin (Laminin-2)
    • Walker-Warburg syndrome: Homozygous FKRP mutations; Met1Val & Cys318Tyr
• FKRP protein
  • Ubiquitous
  • Highest levels: Skeletal muscle; Heart; Placenta
  • Subcellular
    • Golgi
    • Skeletal and cardiac muscle
      • Surrounds myonuclei
      • No change in location with disease mutations
      • Absent from the nuclei of interstitial cells
    • Targeted by N-terminus & tm domain
    • Not secreted
  • Glycosyltransferase
  • Colocalizes with α-Mannosidase II
  • Associated with dystroglycan processing
• 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
  • Proximal > Distal
  • Legs & Arms
  • Legs: Thigh adductors; Psoas; Quadriceps
  • Arms: Periscapular; Deltoid; Biceps; Triceps
  • Face: Mild weakness in some older patients
  • Respiratory failure (30%)
    • May occur while patient still ambulant
    • DMD-phenotype: Onset in later teens
  • Severity
    • Variable: DMD-like to Adult onset myopathy
    • Intrafamilial variability described
  • Asymmetry: Some patients
  • Progression
    • Early onset: Non-ambulant by teens
    • Later onset: Slow; Variable; Some (28%) non-ambulant by 4th to 6th decade
  • 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
  • Muscle fiber size: Variation
  • Necrotic & regenerating muscle fibers
  • Type 1 muscle fiber predominance
  • Connective tissue: Mildly increased
  • Reduced staining for
    • α-Dystroglycan: Especially in Severe disease
      • Selective loss of higher MW forms
      • Less severe loss than in MDC1C
      • Some patients have normal staining
      • DDx of reduced α-Dystroglycan
        • Fukuyama
        • MDC1C
        • MEB
    • α2-laminin (Moderate loss): May be absent on Western blot
  • Normal dystrophin, sarcoglycans & β-dystroglycan
  • Nerve conduction studies: Normal
  • EKG: Normal
  • MRI: Normal CNS or minimal atrophy

• 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

• 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
    • Myopathy with Early Respiratory failure: Dominant
    • Cytoplasmic body myopathy: Dominant
    • Multicore disease: Congenital myopathy + Fatal dilated cardiomyopathy (EOMFC): Recessive
    • Dilated cardiomyopathy 1G: Dominant
    • ? Hypertrophic myopathy (CMH 9)
• Titin protein
• Clinical
  • Usually occurs in families with other members having dominant distal weakness syndrome
  • Onset age
    • Usual: Childhood
    • Range: < 10 years to 3rd decade
  • Weakness
    • Proximal > Distal
    • More severe than in allelic distal myopathy
    • Face: Normal
  • Wasting: Anterior tibial
  • Progression
    • Usual: Wheelchair < 30 years, within 20 years of onset
    • Some patients ambulatory at 60 years
  • No cardiomyopathy
• Laboratory
  • Serum CK: High
  • Muscle biopsy
    • Myopathic
    • No vacuoles
    • Loss of calpain-3
• Mouse model: Homozygous knockout
  • Severe: Lethal
  • Weakness: Distal > Proximal

LGMD 2K (MDDGC1) : with Mental retardation and Reduced α-dystroglycan

• Nosology: Muscular dystrophy-Dystroglycanopathy
• 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

• Epidemiology
  • May be 10% to 20% of LGMD families
  • Females: Less commonly or less severely affected
• Genetics
  • Mutations: > 20 identified
    • Splice site (C1295G; Aberrant splicing of Exon 13)
    • Duplication (c.191 dupA in exon 5): Common in Northern Europe
    • Arg758Cys in exon 20: Common mutation
    • Missense: G231V in exon 8
    • Locations: Distributed all along gene
  • Allelic with
    • Gnathodiaphyseal dysplasia : Dominant
    • Distal myopathy (MMD3): Recessive
  • Genotype-Phenotype correlations
    • Variable phenotypes, mild & severe, with most mutations
• Anoctamin 5 protein
  • Member of family of proteins with 8 transmembrane domains
    • Anoctamins 1, 2 &3 are calcium-activated chloride channels (CaCC)
    • ANO3 mutatins cause: Dominant Craniocervical Dystonia (DYT23)
  • Integral membrane glycoprotein
  • Intracellular
  • Functions: Myogenesis; Osteogenesis
  • Mutations may cause: Defective membrane repair
• Clinical
  • Variability
    • Intrafamilial: Prominent
    • Variant syndromes
      • Distal myopathy
      • Normal strength with high CK
  • Onset
    • Age: Mean = 33 years; Range 11 to 51 years
    • Weakness: Quadriceps, Asymmetric
  • Muscle
    • Atrophy: Quadriceps; Biceps brachii; Lower leg
    • Asymmetric
    • Weakness
      • Legs > Arms
      • Scapular: Biceps
      • Pelvic: Psoas; Quadriceps
      • Posterior leg: See MMD3
      • Distal arms: Normal strength
      • Face: Few patients
      • Progression: Slow
    • Muscle pain: 86%; 50% with, or after, exercise
    • Fatigue: May occur before weakness
    • Calf hypertrophy: Some patients
    • Course: Progressive; Walking retained
    • Respiratory: Normal
  • Contractures: Unusual
  • Cardiac: Usually normal
• Laboratory
  • MRI: Early atrophy of medial quadriceps, hamstrings & adductor magnus
  • Serum CK: Normal to 35,000
  • EMG: Myopathic; Some with spontaneous activity
  • MRI: Asymmetric involvement
• Pathology: Muscle
  • Muscle fibers
    • Size: Varied
    • Necrosis & Regeneration
    • Internal nuclei
    • Splitting
    • Internal architecture: Irregular; Whorled
    • Vacuoles: 2 patients
    • Ultrastructure: Multifocal sarcolemmal lesions
  • Endomysial connective tissue: Increased
  • Inflammation: In severe cases; Endomysial
  • Amyloid: 1 patient; Peri-Vascular & Muscle fiber
  • Dystrophy proteins
    • Dystrophin reduced: 40%
    • Calpain-3 reduced: 45%
    • Dysferlin: Normal
• Variant syndrome: Distal Miyoshi-like myopathy 3 (MMD3)
  • Epidemiology: Dutch & Finnish families
  • Genetics
    • Inheritance: Recessive
    • ANO5 Mutations
      • Missense: Arg758Cys in exon 20
      • Duplication (c.191 dupA in exon 5)
    • Allelic with: LGMD 2L
  • Clinical
    • Onset
      • Age: 2nd & 3rd decade
      • Difficulty running & standing on toes
    • Weakness
      • Calf: Early; Difficulty running & walking on toes
      • Proximal: Ileopsoas; Hamstrings, Gluteus maximum, Hip adductors
    • Hypertrophy: Calf; Extensor digitorum brevis
    • Muscle discomfort: Calves
    • Asymmetry
  • Laboratory
    • Serum CK: 1,500 to 16,000
    • Muscle pathology
      • Cell membrane repair defect
    • Imaging: Medial gastrocnemius & soleus involvement
• Variant syndrome: Normal strength with high serum CK
  • Myalgias
  • Calf hypertrophy
  • Some patients asymptomatic

LGMD 2M (MDDGC4)

• Nosology: Muscular dystrophy-Dystroglycanopathy
• Epidemiology: 5 families; Portuguese, Turkish, French, Israeli Jewish & Indian
• Genetics
  • Mutations
    • Types: Stop & Missense
    • 1167dupA; 1363delG; Arg47X; Ala170Glu; Arg246Gly; Arg307Gln; Tyr371Cys
  • Allelic 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

• Epidemiology: 5 families from UK & Finland
• Genetics
  • Compound heterozygous
  • Mutation type: Truncating
  • Allelic with
    • IBM3, Dominant
    • Early onset myopathy with ophthalmoplegia, Recessive
• MYH2 protein
  • Myosin subtype
  • Location: Type 2A muscle fibers
• Clinical
  • Onset age: Early childhood
  • Weakness
    • Generalized
    • Mild
    • Proximal > Distal
    • Face & Neck
    • Extraocular muscles
      • Severe ophthalmoplegia
      • Ptosis 20%
    • Prognosis: Slow progression with age
  • Muscle wasting
  • Joints: Hypermobility
• Laboratory
  • Muscle pathology
    • Type 2A fibers: Absent
    • Fiber size: Varied
    • Internal nuclei
    • Endomysial connective tissue: Increased
  • EMG: Myopathic
  • Serum CK: Normal
  • Muscle imaging: Selective nvolvement of
    • Leg: Medial gastrocnemius
    • Thigh: Semitendinosus, Gracilis & Vastus lateralis
• Also see: Myopathies with Ophthalmoplegia

Early-onset Myopathy with External ophthalmoplegia ⁷⁸

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

Myosclerosis

• 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

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

Other Dominant Myopathies

• Gene mutations: >50 identified
  • Most mutations located between Exons 3 and 14
  • Most are amino acid substitutions: Glycine most common (Gly-X-Y)
    • Usually in triple helix region
    • Some mutations in globular region
    • Disease pathogenesis: ? Dominant negative effect
  • Inframe deletion in exon 14 of Collagen α1 (IVS14DS, G-A, +1): Common mutation
  • Can also cause disease by stop codon : Produces haploinsufficiency
    • Lower incidence of contractures
  • Other disease correlations
    • Most severe disease: COL6A1 multi-exon out-of-frame deletion; Mutations inside triple helix
    • Milder: Exon-skipping mutations; N-terminal globular region
    • Recessive COL6A2 mutations: Stop & Splicing (c.1770delG & R784H in cis) + Missense (R830W)
  • Allelic 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

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

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

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

• 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

• 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

• Dominant; ? LGMD 1

Other Recessive Myopathies

• Nosology: Congenital disorder of glycosylation, Type 1o (CDG1O)
• 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
    • Necrotic fibers
    • Rimmed vacuoles
    • Fiber splitting
    • Endomysial fibrosis
    • α-Dystroglycan: Reduced

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

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

• Northern Indiana Amish
• Linked to LGMD 2E

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

• 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

• 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

• 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
  

• Epidemiology: Families in Europe & North America, ~14
• Genetics: VMA21 mutations ⁷¹
  • Single nucleotide substitutions
  • Locations: Intron; Splice site; 3' UTR
  • Mutation effects: Reduced VMA21 abundance
• VMA21 protein (Vacuolar H⁺-ATPase homolog)
  • Assembly chaperone for: V-ATPase
    • Principal mammalian proton pump complex
    • May pump 2-3 H⁺ per ATP hydrolyzed
    • Acidify vesicles: Golgi-derived, Clathrin-coated, Synaptic
    • Inhibitor: Bafilomycin
  • Decreased VMA21
    • Raises Lysosomal pH: Increased from 4.7 to 5.2
    • Lysosomal degradative ability: Reduced
    • Autophagy: Blocked
    • Cellular free amino acids: Reduced
    • mTOR pathway & mTOR-dependent macroautophagy: Down regulated
    • Proliferation of large & ineffective autolysosomes
      • Engulf sections of cytoplasm, merge & form vacuoles
  • Disease mechanism
    • Macroautophagic overcompensation: Leads to cell vacuolation & tissue atrophy
• Clinical: Similar patterns among families
  • Onset age
    • 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 (AVSF)
      • Excessive autophagic activity
      • Location: Sarcoplasm; Internal or Near surface
      • Size: 2 to 10 μm
      • Basophilic granules
      • Contents
        • Lysosomal enzymes (Hydrolases)
        • Calcium
        • C5b-9 complement components
        • Cellular debris
        • Acid phosphatase: Variably present
      • Immunostaining
        • Dystrophin: Vacuolar membrane staining
        • LAMP-2 & Sarcoglycans
        • Caveolin-3
        • α1-Antitrypsin: Within vacuoles
      • Vacuolated fibers express polysialylated isoform of NCAM
      • Unable to complete digestion of contents
        • Migrate to myofiber surface
        • Fuse with sarcolemma
        • Exocytosis of phagocytosed material: To extracellular space
      • Differential diagnosis
        • X-linked myopathy with excessive autophagy
        • Danon disease
        • Infantile autophagic vacuolar myopathy
        • Childhood autophagic vacuolar myopathy
        • Adult-onset autophagic vacuolar myopathy with multiorgan involvement
        • LGMD 1A: With other aggregates
  • Basal lamina
    • Affected fibers surrounded by multiple layers
    • Contains Granular material
  • Complement deposits
    • Sarcolemma & vacuoles
    • Granular pattern

• 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%
    • Monophasic severe post-operative weakness: 1 patient ⁸⁴
  • Cardiomyopathy (Nearly 100%)⁷²
    • Symptoms: Chest pain, Palpitations, Syncope, Cardiac arrest.
    • Hypertrophic: Concentric; Impaired LV function; Thick IV septum & posterior walls
    • Left ventricular systolic dysfunction, ejection fraction ~25%
    • Left ventricular cavity enlargement
    • Treatment: Pacemaker or Heart transplantation
    • EKG
      • Abnormal in 100%: Arrhythmia
      • Ventricular preexcitation
      • Wolff-Parkinson-White; Short PR intervals; High precordial voltage
    • Echocardiography: Concentric left ventricular hypertrophy
    • Prognosis: Poor
      • Progression to end stage heart failure in early adulthood
      • Sudden death
  • Mental retardation: 80%; Mild or absent in 40%
  • Hepatomegaly: 35%
  • Foot deformities: 38% of males
  • Retinopathy
    • Loss of pigment in retinal pigment epithelium
    • Reduced visual acuity: Mild
  • Course
    • Some with death in 2nd to 5th decade
    • Cause of death: Cardiac failure
• Laboratory
  • Serum CK
    • High in most (4x to 35x normal; 300 to 3,000)
    • May be normal (10% to 20%)
    • Patients may present with asymptomatic high CK
  • EMG: Myopathic (100%); Myotonia (30%); Spontaneous activity (30%)
  • Nerve conduction tests: Normal
  • EEG: Mild abnormalities in 28%
  • Liver enzymes: High
  • CNS: Normal brain MRI
• Muscle pathology
  • Vacuoles: Similar to XMEA
    • Autophagic: Contain lysosomal enzymes
    • Cytoplasmic: Small solid basophilic granules
    • Histochemistry: Acid phosphatase, Nonspecific-esterase & Acetylcholinesterase staining
    • Immunocytochemistry: Stain for Dystrophin; Laminin; limp-1
    • Ultrastructure: Vacuoles contain glycogen particles & cytoplasmic debris
    • Present in males & females
  • Myopathy: Variation in muscle fiber size
  • Glycogen: Increased or Normal amount; Free & membrane bound
  • Lamp-2 protein staining: Absent with most mutations; Rarely residual LAMP-2A isoform
  • Heart: Fibrosis; Intracytoplasmic vacuoles
• Danon syndrome: Variant with early weakness but no 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
• Variant: Carrier females
  • Frequency
    • > 70% of carriers
    • All eventually have abnormal EKG
  • Clinical
    • Onset
      • Age: 12 to 53 years
      • Cardiac signs
    • Weakness: 33%; Proximal limb & Neck
    • Cardiomyopathy
      • Dilated > Hypertrophic
      • Arrhythmia: Pacemaker in 17%
    • Retinopathy
      • Pigmentary changes: Peripheral
      • Electroretinogram: Abnormal
      • Visual fields: May be abnormal central region
    • Course: Some with death in 4th & 5th decade
  • Laboratory
    • Serum CK: 76 to 643
    • Muscle biopsy
      • Vacuoles
      • LAMP-2 staining: Absent or Reduced
  • Treatment: Cardiac transplantation or Pacemaker
• Danon syndrome: Variant
  • Scapuloperoneal muscular dystrophy with mental retardation & lethal cardiomyopathy

Myofibrillar (Desmin -storage) Myopathies^3,11

Clinical features Pathological features Hereditary types   Congenital     Cap       TPM2: 9p13       TPM3: 1q22       ACTA1: 1q42     MD: SEPN1; 1p36     MD + JEB: Plectin; 8q24     Myopathy: CCDC78; 16p13   MFM1 (LGMD 1E): Desmin; 2q35   MFM2: αB-crystallin; 11q22   MFM3 (LGMD 1A): Myotilin; 5q31   MFM4: ZASP; 10q23   MFM5: Filamin C; 7q32   MFM6: BAG3; 10q25   Myopathy & Respiratory Δ     Type 1: Titin; 2q31     Type 2: 2q21   Restrictive cardiomyopathy   Scapuloperoneal MD: FHL-1; Xq26 Desmin knock-out mouse Also see   Inclusion body myositis   Intermediate filament disorders

Desmin aggregates

Myofibrillar myopathies: General

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

Myofibrillar myopathies: Specific syndromes

Myofibrillar myopathy 1 (MFM1)

• 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
    • Dilated cardiomyopathies: 1F, 1I
    • LGMD 1E
    • ARVD7
    • Recessive disorders
• 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

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

  From HPRD αB-crystallin

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

• 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 (CMD1C)
    • Isolated non-compaction of left ventricular myocardium
  • ~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: Child 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

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

• 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

• 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

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

• 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

• Epidemiology: German & Chinese families
• Genetics: Truncation mutation
  • Mutations
    • German: W2710X
    • Chinese: 2695–2712 del/GTTTGT ins (Exon 18; In-frame)
    • 12-nucleotide deletion in exon 18
    • Filamin C rod & dimerization domains
  • Truncated protein: Abnormal folding; Unable to dimerize properly
  • Allelic with: Distal myopathies
    • Spared anterior leg muscles
    • Upper limb predominance
• Filamin C protein
• Clinical
• Onset
  • Age: 35 to 57 years
  • Weakness: Usually proximal legs
  • Back pain
• Weakness
  • Legs > Arms
  • Usually: Proximal > Distal
  • Respiratory: 50%
  • Other: Hands; Calf weakness, Selective; Neck flexor
• Polyneuropathy: 40%
• Cardiac
  • Some patients
  • Often mild
  • Bundle branch block; Reduced ejection fraction
• GI: Chronic diarrhea in some patients
• Laboratory
  • Serum CK: Mildly elevated, 2x to 8x
  • EMG: Myopathic; Myotonic discharges
  • Muscle pathology: Myofibrillar myopathy
    • Internal nuclei
    • Fiber splitting
    • Necrosis: Isolated fibers
    • Gomori trichrome stain: Hyaline masses; Vacuoles; Rods
    • Aggregates
      • Contain: Filamin C, Desmin, Myotilin, Dystrophin, Sarcoglycans; Dysferlin; Not α-actinin
      • Cytoplasmic
      • Spheroid bodies

• Epidemiology: 2 families
• Genetics
  • Mutation: Pro209Leu in both families
  • Allelic with: CMD 1HH, Cardiomyopathy, Familial dilated
• Protein: Family of Hsp70/Hsc70 molecular chaperone regulators
  • Anti-apoptotic activity
    • Binds to Bcl-2 and PLC-γ
  • Chaperones
    • Binds to the ATPase domain of HSP70 & HSC70 chaperones
    • Inhibits chaperone activity of HSP70 & HSC70: Promotes substrate release
  • Muscle: Z-disk (Colocalizes with myotilin)
• Clinical
  • Onset: Childhood
  • Weakness
    • Proximal > Distal
    • Limb & Axial
    • Respiratory
  • Cardiomyopathy
    • Onset: Teens
    • Restrictive or Hypertrophic
  • Skeletal
    • Rigid spine
    • Scoliosis
    • Contractures
  • Polyneuropathy (1 patient): Axonal & Demyelinating
• 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
• Variant: Dilated cardiomyopathy
  • Mutations: Frameshift, Deletion, Nonsense & Missense
  • Adult onset

• 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 & Disorders ²⁰

• Intermediate filaments: General features
  • Family
    • ~ 65 functional genes
    • Most are unique to multicellular organisms
    • ? Ancestor protein in unicellular organism: Crescentin (In bacteria)
  • Structure
    • Fibrous proteins
    • Central rod domain
      • Coiled coil α-helical
      • Similar structure in most IFs: Different 1° sequences
      • Heptad repeats: Contain Acidic residues
    • amino- & carboxy- termini: Various lengths and sequence
    • 10-nm diameter
    • Soluble unit: Tetramer with two antiparallel dimers
  • Post-translational modifications
    • Farnesylation
    • Phosphorylation: Regulates
      • Filament organization & solubility
      • Association with interacting proteins
      • Susceptibility to degradation during apoptosis
    • Glycosylation
    • Transglutamination:
      • Formation of protective, cornified cell envelope contributing to skin barrier
  • Interactions with other proteins
    • Actin microfilaments (7 nm)
    • Microtubules (24 nm)
  • Locations
    • Most are cytoplasmic
    • Lamins in nucleus
    • Some are integral membrane proteins
  • Functions: Mediate cell-type-specific features of cytoarchitecture
    • Interconnected: With same, or other accessory proteins
    • Form cytoskeletal scaffolding in eukaryotic cells
    • Dynamic: Some are motor proteins
    • No known enzymatic activity
  • 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
    • Myopathy + Right ventricular cardiomyopathy
  • Desmuslin : Muscle; Co-localizes with desmin
  • Filensin : Lens; Cataracts
  • FHL1: Scapuloperoneal muscular dystrophy
  • Glial fibrillary acidic protein (GFAP) : Alexander disease
  • α-Internexin : CNS
  • Lamins: Nuclear
    • Lamin A/C: Emery-Dreifuss muscular dystrophy; Differentiated cells
    • Lamin B : All cell types
  • Nestin : Neuroepithelial stem cells; Muscle cells (Z-band); Fibroblasts
  • Neurofilaments: NF-L; NF-M; NF-H
    • ALS, Sporadic & Familial NF-H tail deletions
    • CMT: NFL
      • 1F
      • 2E
      • AR (2B5)
      • AR-CMT: TRIM2 - NFL are target of ubiquitination
    • 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
  • Titin: Proximal & Respiratory muscle weakness
  • Vimentin : Mesenchyme; Null mutation has no phenotype
• Intermediate filament-associated proteins & mutations
  • αB-crystallin (11q22): Dominant myopathy
  • Bullous pemphigoid antigen 1
  • Desmoplakin : Keratosis palmoplantaris striata II; Dilated cardiomyopathy
  • Emerin: Emery-Dreifuss muscular dystrophy
  • Gigaxonin: Giant axonal neuropathy
  • Plectin: Congenital Muscular Dystrophy with Familial Junctional Epidermolysis Bullosa
• Neurofilament accumulations in acquired neuropathies
  • Giant axonal neuropathy
  • Hexacarbon intoxication
  • Disulfiram
  • Acrylamide
  • β,β-iminodipropionitrile (Proximal initial axon segments; Animal model only)
  • Dimethylaminopropionitrile (Distal intramuscular nerves)
  • Carbon disulfide
  • Diabetes (Distal intramuscular nerves)
  • Non-specific: Chronic neuropathy
  • Motor neuron disease (ALS): Cell body & Initial segment

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

Gomori trichrome

Phalloidin

• 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 Titin (TTN) ; Chromosome 2q31.2; Dominant
  • Epidemiology: Swedish families
  • Genetics
    • Mutation: Missense: Cys30071Arg
    • See: Allelic disorders
  • Titin protein
  • 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.
  
  
• CBM: Distal types
  l Autosomal Dominant
  • Also see: Gowers-Laing, severe phenotype (MYH7)
  • Clinical features
    • Weakness
      • Distal & Proximal weakness
      • Onset in hands
    • Onset: Late 40 to 50 years
    • Progression: To respiratory failure
    • Cardiomyopathy: Heart block; Arrhythmias; Congestive heart failure
  • Laboratory
    • Serum CK: Nomal or slightly elevated
    • EMG: Myopathic; Complex repetitive discharges
    • Muscle pathology
      • Cytoplasmic bodies
      • Myofibrillary inclusions in cytoplasm of Type I muscle fibers
  
  
• Cytoplasmic Bodies: Pathology

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

• Proximal myopathy with Tubular Aggregates, Younger onset ± Ophthalmoplegia ⁸⁶
  l Stromal interaction molecule (STIM1) ; Chromosome 11p15.4; Dominant
  • Epidemiology: 4 families
  • Genetics
    • STIM1 mutations: His72Gln; Asp84Gly; His109Asn; His109Arg
    • Mutation location: EF hand moiety
    • Mutation effect: Induces STIM1 oligomerization
    • Allelic with: Childhood immune deficiency
      • STIM1 mutations: Recessive loss of function
      • Immune effects: T-cell inactivation
      • Other clinical: Hypotonia
      • Muscle: Type 2 fiber atrophy
  • STIM1 protein
    • Single transmembrane protein
    • Location: Endoplasmic reticulum (ER)
    • Function: ER Ca⁺⁺ sensor
      • EF hand motif: Senses & binds Ca⁺⁺
      • Ca⁺⁺ unbound: STIM1 unfolds & oligomerizes via SAM domains
      • Oligomerization
        • Activates Ca⁺⁺-release-activated Ca⁺⁺ channels (CRACs) by direct binding to subunit ORAI1
        • Triggers extracellular Ca⁺⁺ entry
    • Other ER Ca⁺⁺ sensor protein: STIM2
  • Clinical
    • Onset
      • Age: Childhood to Early adult
      • Weakness: Falling, or Difficulty running or Climbing stairs
      • Some patients: Asymptomatic with high CK
    • Weakness
      • Proximal
      • Legs > Arms
      • Slowly progressive: Some patients use cane in 6th decade
      • Respiratory: Varied; VC 49% of predicted to Normal
      • Face: Usually normal
    • Muscle atrophy: Quadriceps (50%)
    • EOM limitation: 50% of families
      • Up-gaze
      • No ptosis
    • Contractures: Ankle; Wrist; Fingers; Knees; Neck
    • Cardiac: Normal
  • Laboratory
    • Serum CK: High; 4x to 27x normal
    • EMG : Myopathic
    • Muscle Pathology
      • Tubular aggregates
        • In Type I & II muscle fibers
        • Vesicular membrane collection
        • Contents: Empty or moderately dense flocculent material
        • Protein constituents
          • Aggregates: SERCA1; Triadin
          • Periphery: RYR1; STIM1
        • Ultrastructure: Single- or double-walled membranes of different diameters
      • Type 2 muscle fiber atrophy: Most patients
    • Hematology: Normal
  
  
• Proximal myopathy with Tubular Aggregates, Adult onset
  l Autosomal Dominant ²⁴
  • Onset: 5th & 6th decade
  • Weakness: Proximal ± Distal
  • Discomfort
    • Muscle pain, cramps
    • Siffness: Exertional
  • Progression: Slow
  • Serum CK: Normal or Mildly high
  • Pathology
    • Tubular aggregates
      • In type II muscle fibers
      • Tubule types: Several
    • Type II atrophy
  
  
• Proximal myopathy with Tubular Aggregates, Younger onset
  l Sporadic or Recessive
  • Male > Female
  • Clinical
    • Onset: Teens
    • Weakness: Proximal
    • Progression: Slow
  • Laboratory
    • Serum CK: Normal or Mildly high
    • Pathology: Tubular aggregates in II > Type I muscle fibers

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

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

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

• 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

• Central Core
• Nemaline (rod) myopathy
• Centronuclear myopathy
• Congenital Muscular Dystrophy with Junctional Epidermolysis Bullosa

• 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