Which protein is primarily implicated in the described muscular dystrophy etiology?

• A. Collagen
• B. Myoglobin
• C. Actin
• D. Dystrophin

Answer: (D)

The question tests understanding of what drives the most common muscular dystrophy form: the stability of the muscle cell membrane during contraction. Dystrophin serves as the crucial link between the internal cytoskeleton (actin) and the extracellular matrix, anchoring the sarcolemma to surrounding structures. When dystrophin is absent or defective, the membrane becomes fragile and tears with each muscle contraction. This leads to calcium influx, activation of degradative pathways, inflammation, and repeated cycles of muscle fiber necrosis with replacement by fibrous and fatty tissue. That membrane-stabilizing role is why dystrophin is the protein most closely implicated in classic dystrophy etiologies such as Duchenne/Becker.

Collagen is a matrix protein, not the membrane anchor responsible for this dystrophy mechanism; myoglobin is just an oxygen-binding protein; actin is a contractile filament but does not by itself stabilize the membrane to prevent dystrophy.