Becker Muscular Dystrophy — SCE Neurology MCQ

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ModerateNeurogeneticsBecker Muscular DystrophySCE Neurology

A 25-year-old man presents with progressive proximal leg weakness, calf pseudohypertrophy, and dilated cardiomyopathy. CK is 12,000 IU/L. Genetic testing shows an in-frame deletion in the dystrophin gene. He is ambulant. What is the most likely diagnosis?

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Correct answer: D — Becker muscular dystrophy

Becker muscular dystrophy (BMD) is an X-linked recessive dystrophinopathy caused by in-frame mutations in the dystrophin gene, resulting in a partially functional but truncated dystrophin protein. It is milder than Duchenne (which has out-of-frame mutations producing no functional dystrophin). BMD presents later (adolescence/adulthood), with slower progression, preserved ambulation into adulthood, and calf pseudohypertrophy. Dilated cardiomyopathy is common and may be the presenting feature. A: DMD has out-of-frame mutations and earlier, more severe presentation (non-ambulant by ~12 years). C: LGMD2I has different genetic basis (FKRP mutations). D: EDMD has contractures and cardiac conduction defects. E: DM1 has myotonia.

Reference: GeneReviews: Dystrophinopathies. https://www.ncbi.nlm.nih.gov/books/NBK1119/