Fragile X Syndrome

Fragile X Syndrome

As part of Autism Awareness Month, our Genetic Counsellors have been working hard to raise awareness about conditions associated with autism spectrum disorder. Fragile X Syndrome has a significant association with autism — it is the most common inherited cause of intellectual disability and the most common single-gene cause of autism.

What Is Fragile X Syndrome?

Fragile X Syndrome (FXS) is a genetic condition caused by a mutation in the FMR1 gene on the X chromosome. The mutation involves an expansion of a CGG repeat sequence in the FMR1 gene — when this repeat expands beyond a certain threshold (more than 200 repeats), the gene is silenced and the FMRP protein it produces is absent or reduced. FMRP is essential for normal brain development.

Who Is Affected?

Fragile X Syndrome affects approximately 1 in 4,000 males and 1 in 8,000 females. Because the FMR1 gene is on the X chromosome, males are typically more severely affected than females (who have a second X chromosome that can partially compensate). Females who carry a premutation (55–200 CGG repeats) may be at risk for Fragile X-associated primary ovarian insufficiency (FXPOI) and Fragile X-associated tremor/ataxia syndrome (FXTAS).

Associated Health Concerns

• Intellectual disability (mild to severe)

• Autism spectrum disorder or autistic-like behaviours

• Attention deficit hyperactivity disorder (ADHD)

• Anxiety and social difficulties

• Speech and language delays

• Seizures (in some individuals)

• Distinctive physical features (large ears, long face, flexible joints)

The Importance of Genetic Testing and Counselling

Genetic testing for Fragile X Syndrome can confirm a diagnosis, identify carriers in the family, and guide reproductive decision-making. Genetic counselling is essential for families — helping them understand the inheritance pattern, the implications for other family members, and the management and support options available.