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For further information, see CMDT Part 24-36: Myopathic Disorders

Key Features

  • Inherited myopathic disorders are subdivided by

    • Mode of inheritance

    • Age at onset

    • Clinical features (Table 24–10)

  • Duchenne muscular dystrophy

    • Due to a genetic defect on the short arm of the X chromosome

    • Affected gene codes for the protein dystrophin, which is almost absent from diseased muscles

    • Genetic defect is detectable in pregnancy

  • Becker muscular dystrophy

    • Dystrophin levels are generally normal

    • Protein is qualitatively altered

Table 24–10.Selected muscular dystrophies (listed in order of anatomic location and physiologic underpinning).1

Clinical Findings

  • Muscle weakness, often in a characteristic distribution

  • Age at onset and inheritance pattern depend on specific dystrophy

  • Duchenne dystrophy

    • Pseudohypertrophy of muscles

    • Intellectual disability

    • Skeletal deformities, muscle contractures, and cardiac involvement

Diagnosis

  • Genetic testing

  • Muscle biopsy occasionally needed

Treatment

  • Antisense oligonucleotides

    • Three agents are approved by the FDA for treatment of Duchenne muscular dystrophy

      • Eteplirsen appears to benefit those patients with a dystrophin mutation amenable to exon 51 skipping

      • Golodirsen and viltolarsen benefit those with a mutation amenable to exon 53 skipping

    • Treated patients had more functional dystrophin on muscle biopsy than controls and a slower rate of disease progression than matched historical controls

  • Prednisone (0.75 mg/kg orally daily or 10 mg/kg orally given weekly over 2 days) or deflazocort (0.9 mg/kg orally daily) compared to placebo

    • Improves muscle strength and function in boys with Duchenne dystrophy

    • However, side effects need ...

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