Muscular Dystrophies

Muscular Dystrophies is a topic covered in the 5-Minute Pediatric Consult.

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Basics

Description

  • Muscular dystrophies (MDs) are a heterogeneous group of disorders characterized by a slow degeneration of muscle with consequent weakness and contracture deformity. Cardiac muscle can be involved in some forms.
  • MDs with childhood onset can be divided into five groups:
    • Dystrophinopathies (i.e., Duchenne MD [DMD], Becker MD [BMD])
    • Limb-girdle MD (LGMD)
    • Congenital MD (CMD)
    • Facioscapulohumeral MD (FSH-MD)
    • Emery-Dreifuss MD (EDMD)
  • Types of MDs can be differentiated by their clinical features (i.e., pattern of muscle weakness, joint contractures), age of onset, genetic test results, and/or muscle biopsy.

Epidemiology

  • Dystrophinopathies
    • DMD: 1 per 3,500 boys (most common)
    • BMD: 1 per 30,000 boys
  • LGMD (childhood onset): 5 to 10 per million
  • CMD (all types): 1 to 10 per 100,000
  • FSH-MD: 1 per 20,000
  • EDMD: 1 per 300,000

Risk Factors

Genetics

Genetic testing is clinically available for most MDs:

  • Dystrophinopathies (DMD/BMD): X linked
    • DMD exon duplication/deletion in 70% cases
    • DMD point mutation in almost 30% cases
    • New mutations of the dystrophin gene are common, and hence, most cases have no affected relatives despite X-linked recessive inheritance. New mutations in the dystrophin gene are found frequently in the mothers of affected boys.
  • LGMD: Most childhood-onset LGMDs are autosomal recessive.
    • Sarcoglycanopathies (LGMD2C–F) make up roughly 70% of childhood-onset LGMD.
    • LGMD2I (FKRP): 5% childhood-onset LGMD
  • CMD: most autosomal recessive (12 genes)
    • Nonsyndromic (LAMA2, COL6A1 to COL6A3)
    • Syndromic (e.g., POMT1, POMGT1, FKRP)
  • FSH-MD: autosomal dominant (D4Z4 deletion)
  • EDMD: X linked (EMD or FHL1 mutations) or autosomal dominant (LMNA mutation)

Pathophysiology

  • Deficient or defective muscle fiber proteins causing fiber dysfunction and/or increased membrane fragility
  • Muscle biopsy: increased variability in muscle fiber size (i.e., degenerating, regenerating, and necrotic fibers), split muscle fibers and increased internal nuclei, fibrosis. Immunohistochemistry may note decreased/absent sarcolemmal proteins (e.g., DMD, LGMD, CMD).

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Citation

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TY - ELEC T1 - Muscular Dystrophies ID - 617456 ED - Cabana,Michael D, BT - 5-Minute Pediatric Consult UR - https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617456/all/Muscular_Dystrophies PB - Wolters Kluwer ET - 8 DB - Pediatrics Central DP - Unbound Medicine ER -