Book excerpt: 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—and all too often, they suffer in silence. The Carriers investigates this common but still little-known genetic condition and its life-altering consequences. Anne Skomorowsky reveals how this disorder afflicts families across generations, telling the stories of the mothers and grandparents of fragile X patients and considering how genes interact with family dynamics. She interweaves the personal narratives and family histories of the people affected by fragile X disorders with clear and accessible explanations of the science behind them. Skomorowsky unpacks the latest research on the fragile X mutation and explores the history of its discovery. She highlights the roles of women as carriers, caregivers, and researchers who have made astonishing scientific breakthroughs over the last three decades. The Carriers is an essential book for fragile X families, including those just learning they are carriers, and for all readers interested in the complexities of heredity, the ethical dilemmas of genetic medicine, and the relationship between genes and personality.