Duchenne Muscular Dystrophy and Becker's Muscular Dystrophy

Muscular dystrophy (MD) refers to a group of nine genetic diseases that cause progressive weakness and degeneration of muscles used during voluntary movement; Duchenne Muscular Dystrophy is the most common form seen in children

Aetiology

  • X-linked recessive disorders involving genes responsible for dystrophin, though one-third of cases are spontaneous mutations

Pathophysiology

  • Dystrophin is essential for cell membrane stability
  • In DMD there is an absence of dystrophin
  • In Becker’s dystrophy, dystrophin is present but levels are low - progresses much more slowly (but is less common)

Clinical presentation

  • Delay in motor development, some have more global delay
  • Onset of weakness 3-4 years - pelvic and shoulder girdles
    • Gower's sign - arms used to compensate for weakness of pelvic girdle muscles getting up from the floor
    • Toe walking
    • Exaggerated lumbar lordosis
  • Calf hypertrophy
  • In DMD, severe disability is typical by age 10
  • Becker’s muscular dystrophy is less severe than Duchenne and weakness only becomes apparent in young adults

Investigations

  • Raised serum creatine kinase
  • Molecular genetic testing - screen for deletions and sequence gene (constitutional DNA from blood or saliva)
  • EMG
  • Muscle biopsy
  • Testing for mutation in female relatives wishing to know carrier status

Management

  • There is no curative treatment but new gene-editing therapies are in development
  • Steroids may delay progression
  • Physiotherapy helps prevent contractures in the later stages
  • Non-invasive respiratory support and multidisciplinary care improve life expectancy
  • Death in 20s typical in DMD - involvement of respiratory and cardiac muscles