Which protein stabilizes muscle fibers during contraction and is implicated in MD when deficient?

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

Answer: (D)

Dystrophin is the stabilizing protein implicated in muscular dystrophy when deficient. It sits inside the muscle cell membrane and anchors actin filaments to proteins in the extracellular matrix, forming a link that spreads the mechanical stress of contraction across the sarcolemma. This membrane-stabilizing connection protects muscle fibers from tears during contraction. When dystrophin is missing or defective, the membrane becomes fragile, calcium influx and enzymes damage the fibers, and muscle cells die, leading to progressive weakness and replacement by fat and fibrous tissue seen in Duchenne and Becker muscular dystrophy. Other sarcomere proteins like titin, actin, and myosin are essential for contraction themselves, but their deficiencies don’t produce the same membrane-stability defect that drives these muscular dystrophies.