Which gene mutation causes Duchenne and Becker muscular dystrophy, and what is the encoded protein?

• A. Mutations in the LMNA gene encoding lamins A/C
• B. Mutations in the DMD gene encoding dystrophin
• C. Mutations in the SMN1 gene encoding survival of motor neuron protein
• D. Mutations in the DMD gene encoding dystrobrevin

Answer: (B)

Mutations in the dystrophin gene (DMD) cause Duchenne and Becker muscular dystrophy. Dystrophin is a large cytoskeletal protein that links actin inside the muscle fiber to the dystrophin-glycoprotein complex in the sarcolemma, providing mechanical stability to the membrane during muscle contraction. When dystrophin is absent or defective, the membrane becomes fragile, muscles experience repeated injury and progressive weakness. Duchenne typically results from mutations that abolish dystrophin production, while Becker results from mutations that allow some truncated, partially functional dystrophin, leading to a milder course.

Other options refer to different proteins and diseases: LMNA encodes lamins A/C, SMN1 encodes the survival of motor neuron protein, and the DMD gene does not encode dystrobrevin (a different protein encoded by another gene).