GPAtlas🧭 When to suspect
Suspect Duchenne muscular dystrophy (DMD) in any boy with delayed motor milestones – classically not walking by 18 months – together with:
• A waddling gait.
• Frequent falls.
• Difficulty running, jumping or climbing stairs.
• Enlarged calves (pseudohypertrophy).
A Gower’s sign (the child uses his hands to ‘climb up’ his own legs to stand) is the best clue: check creatine kinase (CK) immediately.
DMD is an X-linked recessive condition caused by mutations in the dystrophin gene, so it almost exclusively affects boys.
• Around 100 boys are born with DMD each year in the UK, with roughly 2,500 living with the condition at any time.
• About one-third of cases arise from a new (de novo) mutation, so a negative family history does not exclude it.
• There is no newborn screening for DMD in the UK, which makes alertness to the clinical pattern – and a low threshold for checking CK – the only route to early diagnosis.
Becker muscular dystrophy (BMD) sits on the same spectrum but is milder, with later onset and slower progression; many remain ambulant into adulthood. Both are dystrophinopathies, and the key distinction follows the ‘reading-frame rule’.
| Feature | Duchenne (DMD) | Becker (BMD) |
|---|---|---|
| Dystrophin | Absent (out-of-frame or nonsense mutation) | Reduced/truncated but partly functional (in-frame mutation) |
| Typical onset | Age 2–5 (often diagnosed ~5) | Teens or early adulthood |
| Ambulation | Wheelchair usually by early teens | Often ambulant into adulthood |
| Course | • Rapidly progressive • Life-limiting |
Slower, more variable |
| CK | Massively raised (often 10–100× normal) | Raised, though often less markedly |
Also consider the diagnosis in a boy with unexplained global developmental or speech/language delay, as DMD is associated with neurodevelopmental difficulties (learning, attention and autistic-spectrum traits) that may present before the motor signs are obvious.
Source: NICE NR1 (DMD Care UK) · UK National Screening Committee · Muscular Dystrophy UK
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