A 24-month-old boy has been diagnosed with Duchenne muscular dystrophy (DMD). The parents come to speak with the health care team about having other children. This is an X-linked recessive disorder, and the mother is a carrier. The nurse correctly explains
“There is a 50% chance a male child will have DMD.”
“There is a 100% chance a female child will have DMD.”
“There is a 25% chance a female child will be a carrier for DMD.”
“There is a 100% chance a male child will have DMD.”
Number 1 is correct.
DMD is carried by an X-linked recessive gene. It is transmitted by the mother: If the mother is a carrier, one of her X chromosomes has the mutation. Therefore, there is a 50% chance a female child will be a DMD carrier (females have two X chromosomes). There is a 50% chance a male child will inherit the disease and have DMD (males only have one X chromosome).
