Duchenne and Becker muscular dystrophy
- Lesion
Boys missing the protein dystrophin have muscle fibres that tear with every contraction; weakness starts in early childhood and the heart fails later.
What it is
Duchenne and Becker muscular dystrophy are X-linked diseases of the dystrophin gene, one of the largest human genes. Dystrophin links the actin cytoskeleton to the dystroglycan complex and the basement membrane, stabilizing the sarcolemma during contraction. Frameshift or nonsense mutations abolish it (Duchenne, onset in early childhood, loss of walking around the early teens), while in-frame deletions leave a shorter, partly working protein (Becker, milder and later). Fibres tear, necrose and regenerate until satellite cells are exhausted and muscle is replaced by fat and fibrous tissue. Gene-directed treatments include exon skipping, micro-dystrophin gene therapy and, in spinal muscular atrophy, antisense and AAV gene replacement.
Structure
- Early: scattered necrotic fibres with macrophages and clusters of basophilic regenerating fibres.
- Hypercontracted, large, rounded opaque fibres from calcium influx.
- Later: marked variation in fibre size, central nuclei, endomysial fibrosis and fatty replacement; calf enlargement from fat (pseudohypertrophy).
- Heart: interstitial fibrosis of the left ventricle, dilated cardiomyopathy.
- Dystrophin immunostaining: absent in Duchenne (except rare revertant fibres), patchy and weak in Becker.
Step by step
- Mutation in the DMD gene on Xp21 removes or truncates dystrophin.
- Without dystrophin, the dystrophin-glycoprotein complex is lost and the sarcolemma becomes fragile.
- Contraction tears the membrane; calcium enters and activates proteases, and fibres necrose.
- Satellite cells regenerate fibres many times until they are exhausted.
- Muscle is replaced by fat and fibrous tissue; respiratory and heart muscle fail.
Duchenne vs Becker
| Feature | Duchenne | Becker |
|---|---|---|
| Mutation | Frameshift or nonsense (out of frame) | In-frame deletion |
| Dystrophin | Absent | Reduced or shortened |
| Onset | Age 2 to 5 | Late childhood to adulthood |
| Walking | Lost around the early teens | Kept into adulthood |
| Heart | Cardiomyopathy in adolescence | Cardiomyopathy, sometimes the main problem |
Clinical notes
- Gowers sign: the child climbs up his thighs with his hands to stand, from hip and thigh weakness.
- Glucocorticoids slow progression; heart and lung care has extended survival.
- Mild intellectual impairment occurs in some, because brain isoforms of dystrophin are also lost.
Test yourself
Think of the answer, then tap the question to see it.
What does dystrophin do?
It links the actin cytoskeleton to the dystroglycan complex and basement membrane, stabilizing the sarcolemma.
Why is Becker dystrophy milder than Duchenne?
In-frame deletions leave a shorter but partly functional dystrophin, whereas Duchenne mutations abolish it.
What is pseudohypertrophy of the calves?
Calf enlargement from replacement of muscle by fat and fibrous tissue, not from bigger muscle.
How does exon skipping work?
Antisense oligonucleotides make the splicing machinery skip an exon, restoring the reading frame so a shorter dystrophin is made.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Duchenne and Becker muscular dystrophy: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2025); Muscular Dystrophy | MD | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025); Spinal muscular atrophy: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.