Fragile X syndrome (FXS) is an inherited condition that causes varying degrees of intellectual disability, autism, and developmental and behavioral problems.
FXS is caused by pathogenic (disease-causing) variants in the FMR1 gene on the X chromosome and exhibits X-linked dominant inheritance. This means that one pathogenic variant is enough to cause the disease in both males (who have one X chromosome and one Y chromosome) and females (who have two X chromosomes).
Typically, males with a pathogenic variant can experience more severe symptoms compared to females with a pathogenic variant. The risk of being a carrier is based on a person’s ancestry or ethnic background. For example, individuals of Ashkenazi Jewish descent have a 1 in 58 chance to be a carrier.
Carriers may be at an increased risk for fragile X-associated tremor/ataxia syndrome (FXTAS), premature ovarian insufficiency (FXPOI), and fragile X-associated neuropsychiatric disorders (FXAND). If you are found to be a carrier, a genetic counselor can talk to you in more detail about these risks and what it means.
Another name for this condition is FMR1-related conditions.
Revised June 2022