What type of muscular dystrophy is caused by a defective gene affecting proteins in the sarcolemma?

Duchenne muscular dystrophy (DMD) is the correct answer because it is specifically caused by a mutation in the dystrophin gene, which is responsible for producing the dystrophin protein. This protein is crucial for maintaining the integrity of the sarcolemma, the membrane surrounding muscle fibers. When dystrophin is absent or defective, muscle cells become susceptible to damage during contraction, leading to progressive muscle weakness and degeneration, which are characteristic features of DMD.

In contrast, while other types of muscular dystrophy, such as Limb-girdle and Becker, also involve genetic mutations that affect muscle structure or function, they do not specifically involve the sarcolemma in the same direct manner as Duchenne muscular dystrophy does. Limb-girdle muscular dystrophies can involve a variety of proteins, and Becker muscular dystrophy is a milder form related to DMD but generally involves a partially functional dystrophin. Emery-Dreyfuss muscular dystrophy has distinct genetic causes and involves different proteins altogether, particularly those related to the nuclear envelope rather than the sarcolemma.

Therefore, Duchenne muscular dystrophy stands out as the condition directly linked to the defective gene affecting the sarcolemma proteins.