Duchenne muscular dystrophy is inherited in which pattern?

• A. Autosomal dominant
• B. X-linked recessive
• C. Autosomal recessive
• D. Mitochondrial

Answer: (B)

X-linked recessive inheritance explains Duchenne muscular dystrophy. The dystrophin gene is on the X chromosome, so males, with only one X, develop the disease if that X carries the mutation. Females have two X chromosomes, so one mutated copy usually makes them carriers and often asymptomatic due to protective effects from the second X. An affected male passes the mutated X to all daughters (who become carriers) and to none of his sons, while a carrier mother has a 50% chance with each pregnancy to have a son who is affected and a daughter who is a carrier. This pattern accounts for the strong male predominance and the absence of father-to-son transmission. The other inheritance patterns don’t fit this usual family pattern.