How can two unaffected people have a child who has Duchenne muscular dystrophy?

Although rare, this is possible if both parents are carriers of the genetic mutation that causes Duchenne muscular dystrophy (DMD). Carriers of DMD typically do not show symptoms of the disease, but they can pass the mutated gene on to their children.

When a carrier mother and a carrier father have a child, there is a 25% chance that the child will have DMD, a 25% chance that the child will be a carrier, a 25% chance that the child will be an unaffected female, and a 25% chance that the child will be an unaffected male.

It's important to note that the probability of having a child with DMD is the same for each pregnancy, regardless of whether the couple has had an affected child in the past.