The Carriers

A tiny mutation on the X chromosome can shape a family’s history. Passed down from a “carrier” parent to a child, fragile X syndrome is the most common inherited cause of intellectual disability and autism. Beyond that—and a rarity among genetic disorders—some fragile X carriers not only transmit the mutation but also experience related conditions themselves. In such cases, carriers can have tremors, infertility, and psychiatric disorders that complicate raising children with fragile X syndrome—