Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked recessive loss-of-function disorder of the DMD gene. The gene produces dystrophin, a structural protein that links the muscle cell’s internal contractile framework to the membrane and surrounding support structures. Dystrophin functions like a shock-absorbing tie: without it, repeated contraction—especially forceful lengthening or eccentric contraction—causes microscopic tears in the sarcolemma. Those tears allow calcium influx and leakage of muscle enzymes, including creatine kinase (CK). Repeated injury activates proteases, inflammation, and fibrosis; functioning muscle is gradually replaced by fat and scar tissue. The result is progressive proximal weakness, initially most visible in the hips and thighs. The same disease process affects cardiac muscle and the diaphragm. A child may therefore have significant myocardial fibrosis or declining ventilatory reserve before reporting palpitations, dyspnea, or exercise intolerance. DMD care must screen for these complications even when the child appears clinically stable. DMD usually affects boys because they have one X chromosome. Becker muscular dystrophy is the important genetic contrast: partially functional dystrophin usually produces a later-onset, slower, or less severe phenotype. The mutation’s reading-frame effect can help...