Genetic and Metabolic MedicineTier 1Disease (DEADMAN)

Becker muscular dystrophy

Description

X-linked recessive dystrophinopathy - reduced/abnormal (not absent) dystrophin
Milder, later-onset, more variable course than Duchenne

Epidemiology

~1 in 18,000-30,000 male births - roughly 1/5 the frequency of DMD
Onset later - typically childhood to early adulthood, wide range

Aetiopathogenesis

DMD gene mutation in-frame -> truncated but partially functional dystrophin produced
- Contrast DMD: out-of-frame -> no dystrophin
Same gene, mutation-reading-frame determines phenotype severity

Diagnosis

CK elevated (usually less than DMD but still markedly raised)
Genetic testing (deletion/duplication analysis) - confirms, defines frame
Later walking difficulty, cramps with exertion, calf pseudohypertrophy
Can present purely as isolated dilated cardiomyopathy or asymptomatic hyperCKaemia - low threshold to test CK in young men with cardiomyopathy

Management

MDT as for DMD, tailored to slower course
Cardiac surveillance is the priority - echo/CMR periodically; cardiomyopathy may outstrip skeletal muscle severity
- ACEi/beta-blocker at first sign of LV dysfunction
Physiotherapy, orthotics, exercise as tolerated (avoid high-intensity eccentric exercise - theoretical risk of accelerated damage)
Corticosteroids - evidence far weaker than in DMD, not routine
Respiratory surveillance if advanced disease

Associations

Dilated cardiomyopathy - can be the dominant/presenting feature
Cognitive impairment less frequent/severe than DMD

Natural history & complications

Highly variable - some remain ambulant into middle age, others progress like a mild DMD
Life expectancy near-normal to moderately reduced, cardiomyopathy is the main determinant of mortality
Female carriers - as for DMD, minority develop cardiomyopathy/mild weakness -> warrants cardiac screening

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