The absence or deficiency of which protein underlies Duchenne muscular dystrophy?

• A. Dystrophin
• B. Myosin
• C. Actin
• D. Titin

Answer: (A)

Duchenne muscular dystrophy is caused by the absence of dystrophin, a protein that links the muscle cell’s internal cytoskeleton to the surrounding extracellular matrix through the dystrophin-glycoprotein complex. This connection acts as a shock absorber during muscle contraction. Without dystrophin, the muscle cell membrane becomes fragile, allowing tears to form; calcium leaks into the cells and activates enzymes that break down proteins, leading to muscle fiber death. Over time, damaged fibers are replaced with fat and fibrous tissue, producing the characteristic progressive weakness and early loss of ambulation seen in Duchenne.

The other proteins listed—myosin, actin, and titin—are essential structural components of muscle, but Duchenne specifically results from the lack of dystrophin. (Becker muscular dystrophy involves some dystrophin present but reduced or abnormal, which explains its typically milder course.)