DMD is caused by the absence of which protein?

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

Answer: (B)

Dystrophin is the missing protein in Duchenne muscular dystrophy. It serves as a crucial link between the internal scaffolding of muscle fibers (the actin cytoskeleton) and the surrounding membrane via the dystrophin-glycoprotein complex. This connection stabilizes the sarcolemma during contraction. When dystrophin is absent, the membrane becomes fragile and tears during muscle use, allowing calcium to flood into cells and triggering damaging enzymatic processes that lead to muscle fiber death. Over time, this causes progressive weakness, especially in proximal muscles, and pseudohypertrophy of the calves. Other muscle proteins like actin, myosin, and titin are essential for contraction and structure, but their loss doesn’t produce the characteristic Duchenne pattern in the same way dystrophin deficiency does.