Duchenne muscular dystrophy is caused by absence of which protein?

• A. Dystrophin
• B. Myosin
• C. Collagen
• D. Elastin

Answer: (A)

Muscle membrane stability during contraction hinges on dystrophin, which acts as a critical link between the cytoskeleton inside the muscle fiber and the surrounding extracellular matrix. When dystrophin is missing, as in Duchenne muscular dystrophy, this link is lost and the sarcolemma becomes fragile. Repeated muscle contractions cause tears in the membrane, calcium floods the cell, proteases activate, and muscle fibers undergo necrosis. Over time, these fibers are replaced with fibrofatty tissue, leading to progressive proximal weakness that begins in early childhood and is more evident in boys.

The other proteins listed have different roles: myosin is the motor protein that powers contraction inside the cell, while collagen and elastin are components of connective tissue in the extracellular matrix. They do not provide the membrane-stabilizing connection that dystrophin normally supplies, so their absence does not produce the same Duchenne phenotype.