Duchenne and Becker share which inheritance pattern?

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

Answer: (C)

Duchenne and Becker muscular dystrophy are inherited through an X-linked recessive pattern because the faulty gene, dystrophin (DMD), is on the X chromosome. A single mutated X is enough to cause disease in males, who have only one X, while females typically are carriers because they have a second, normal X to compensate. A carrier mother has about a 50% chance to pass the mutated X to her sons (who would be affected) and to her daughters (who would be carriers). An affected father would pass the mutated X to all daughters (making them carriers) but not to his sons. The difference in severity between Duchenne and Becker comes from the specific mutations: Duchenne usually results from mutations that abolish dystrophin, while Becker results from mutations that allow some dystrophin to be produced.