Duchenne Muscular Dystrophy

DMD results from loss-of-function mutations (65% large deletions, 10% duplications, 25% point mutations/small indels) in the DMD gene at Xp21.2, the largest human gene spanning 2.4 megabases. The reading frame rule predicts severity: out-of-frame mutations cause DMD (no functional dystrophin), while in-frame mutations cause the milder Becker muscular dystrophy (truncated but partially functional dystrophin). Dystrophin anchors the subsarcolemmal cytoskeleton to the dystrophin-associated glycoprotein complex, protecting the membrane during eccentric contractions. Loss of dystrophin leads to sarcolemmal microinjury, calcium-mediated protease activation, mitochondrial dysfunction, and chronic inflammatory fibrosis. The clinician manages the complete spectrum of DMD care including prescribing corticosteroids, initiating cardioprotective therapy, managing respiratory decline, overseeing molecular therapies (exon-skipping, gene therapy), and coordinating multidisciplinary care through disease progression.