Fragile X Syndrome (FXS) is the most common inherited cause of intellectual disabilities and intellectual impairment. It is caused by a single gene in the DNA not producing a protein crucial for neurological development and brain function. According to the CDC prevalence of FXS in males is approximately 1 in 7,000 and in females 1 in 11,000. There is currently no cure for Fragile X.

Fragile X can appear in both sexes, but it affects males and females much differently. The disparity in symptoms is caused by inheritance patterns and the biological differences between the sexes. Symptoms can range from mild to severe cognitive, behavioral, and physical disabilities and developmental delays, as well as difficulty communicating and engaging in social activities.

Fragile X features can include:


  • intellectual disabilities, ranging from mild learning disabilities to more severe intellectual impact
  • attention deficit and hyperactivity, particularly in young children
  • anxiety and unstable mood
  • autistic behaviors and is the most common known genetic (“single gene”) cause of autism
  • sensory integration problems, such as hypersensitivity to loud noises or bright lights
  • speech delay, with expressive language more severely affected than receptive language.
  • seizures (epilepsy) affect about 25% of people with Fragile X

Early diagnosis through genetic testing is a pillar of our foundation, because the sooner testing can be done, the sooner families can take the next steps toward finding support. Interventions such as speech therapy, occupational therapy, and special education can help kids with Fragile X syndrome reach their full potential while adding both joy and normalcy to their lives. Learn more about Fragile X here.


Fragile X in females is less common and less known by the public. Because girls have two X chromosomes, one of which can compensate for the mutated gene, Fragile X can result in milder symptoms or even the absence of apparent signs. Unless early testing is done, the condition can remain undiagnosed for years. 

Females with Fragile X might experience anything from mood disorders and anxiety to problems with infertility and hormonal health. In terms of cognitive and intellectual abilities, girls with Fragile X may have learning disabilities and difficulties in an academic setting. As young girls and teens, they may also struggle to relate to their peers, as the syndrome can impair social-emotional development. This can present as difficulty understanding social cues, communicating, and interacting socially. Fragile X can also result in a higher likelihood of experiencing primary ovarian insufficiency (POI). Often, women don’t find out they have Fragile X until they have trouble conceiving.

It's important to note that not all females with Fragile X will display the same set of symptoms, and the level of impairment can vary widely. Our experience underscores the challenges of identifying the less severe symptoms of Fragile X in females. That said, there are amazing resources that can help at all stages of life. Learn more about our Resources + Partners.