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Last updated: 04 January 2025 Print

Duchenne Muscular Dystrophy

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Becker muscular dystrophyDuchenne Muscular DystrophyDystrophinopathies

Duchenne muscular dystrophy (DMD), followed by Becker muscular dystrophy (BMD) and the relatively new phenotype DMD associated dilated cardiomyopathy (DCM) are among the most recognized of a group of X-linked muscle disorders called dystropinopathies. They also include other conditions caused by dystrophin mutations, such as X-linked cardiomyopathy and isolated quadriceps myopathy.

Duchenne Muscular Dystrophy (DMD)

  • Epidemiology: Most common muscular dystrophy of childhood, affecting 1 in 5000 boys.
  • Cause: Mutations in the dystrophin gene.
  • Age of Onset: Symptoms typically present between 3-5 years.
  • Clinical Features:
    • Common: Motor delay, gait abnormalities, frequent falls, difficulty rising from the ground.
    • Less Common: Language/global developmental delay, raised serum creatine kinase, or hepatic transaminases.
    • Typical Signs: Proximal lower limb and trunk weakness, waddling gait, prominent calves, positive Gowers’ sign, and neck flexor weakness.

    Becker Muscular Dystrophy (BMD)

    • Initial increase in motor skills until age 6, followed by progressive weakness.
    • Loss of independent ambulation by age 13.

    Key Complications in DMD

    1. Respiratory:
      • Chronic restrictive lung disease from around 12 years of age.
      • Sleep-disordered breathing progressing to nocturnal and diurnal hypercapnia.
      • Exacerbated by scoliosis.
    2. Cardiac:
      • Dilated cardiomyopathy (affects all patients over 18).
      • Asymptomatic in DMD due to low physical activity.
      • More symptomatic and severe in BMD.
    3. Cognitive:
      • Lower verbal IQ compared to performance IQ.
      • Associated neurodevelopmental conditions such as ADHD and autism spectrum disorders.
    4. Orthopedic Complications in DMD
    • Respiratory: Chronic restrictive lung disease, sleep-disordered breathing, nocturnal and diurnal hypercapnia.
    • Cardiac: Dilated cardiomyopathy, arrhythmias, with early signs such as resting tachycardia.
    • Cognitive: Lower average IQ (verbal IQ more affected), ADHD, autism spectrum disorders.

    Female Carriers of Dystrophin Mutations

    • Epidemiology: Less common and milder than DMD.
    • Cause: Mutations in the dystrophin gene, similar to DMD.
    • Clinical Features:
      • Independent ambulation typically persists beyond age 16.
      • Variable onset of weakness; some individuals remain ambulant throughout life.

      Genetic Basis of DMD

      • Higher incidence of symptomatic cardiomyopathy compared to DMD.
        • Contractures:
          • Commonly affect ankles, knees, iliotibial bands, and hips.
          • Lead to characteristic lumbar lordosis and toe-walking while ambulant.

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