Introduction to fragile X syndrome

Fragile X syndrome (FXS) is the most common known inherited cause of developmental disability. It occurs in approximately one in 3600 to 4000 people in the general population. Fragile X syndrome is an X-chromosome–linked condition that affects both males and females.

Fragile X syndrome is associated with a varying range of developmental, physical, behavioural and emotional characteristics (see Clinical characteristics of fragile X syndrome). The clinical presentation of fragile X syndrome persists across a normal lifespan.