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Fragile X Syndrome

​​​​​​​​​​​​​​​​​​​​​​​​​Fragile X syndrome (FXS) is an identifiable genetic disorder that is one of the more common heritable forms of intellectual disability. FXS and other fragile X-associated disorders are caused by mutations in the Fragile X Mental Retardation 1 gene (FMRI). Any child with unexplained developmental delay, intellectual disability, and/or autism spectrum disorder should receive genetic testing for FXS. 

Support for Patients

Pediatricians can support early identification and evaluation, which empowers families to make informed decisions about FXS-specific services for their child, as well as family planning. A diagnosis also helps assess comorbidities and associated conditions. 

  • Ensure that all children with developmental delay, intellectual disability, and/or autism spectrum disorder are considered for a genetic evaluation.

  • Use a family history tool to evaluate for a family history of related problems that can be seen in fragile X-associated disorders:
    • A history of ataxia or "Parkinson-like" tremors in older males and some femailes on the maternal side.
    • A history of early menopause or fertility problems on the maternal side.
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​​Fragile X Myth Busters 

There are many myths associated with FXS that can contribute to a delayed or missed diagnosis. Here are some of the more common myths:

    Myth: There is no value in making a diagnosis of FXS if there is no cure.

    Fact: Although currently there is no cure for FXS, there are important support treatments that can be applied once the diagnosis is known. These include educational and therapeutic approaches tailored to individual strengths and weaknesses, screening for and treatment of medical issues, and behavioral treatment methods.  Having a diagnosis also enables families to receive counseling for family planning, and for them to connect with support groups of other families affected by FXS.

    Myth: All FXS patients can be recognized by their unusual physical features

    Fact​: Individuals with FXS may have dysmorphic features like prominent ears, a long, narrow face, and large testes after puberty, but many children do not have any characteristic features. Some physical features may not start to develop until puberty, if at all, but can sometimes be seen in younger children too.

    Myth: Girls cannot have FXS, and boys with FXS are always severely affected.

    Fact: ​Both girls and boys can have FXS. Symptoms are usually more severe in boys, but both boys and girls can exhibit symptoms ranging from normal functioning to severe intellectual disability.

    MYTH: FXS is diagnosed using a chromosome test or microarray.

    Fact: FXS cannot be detected with a standard chromosome test or microarray. A specific test called the "FMR1 DNA Test for Fragile X" must be ordered.

    Myth: There has to be a family history of FXS for a child to have the condition.

    ​Fact: Because the FXS mutation is an expanding mutation that can become bigger when passed on to the next generation, diagnosed individuals may lack a recognized family history of FXS. However, a family history of other fragile X-associated disorders, such as tremors and early menopause, can be an indication that a child with unexplained developmental delay, intellectual disability or autism has these features because of unrecognized FXS in the family.

Myth Busters for Providers, Fragile X Syndrome (PDF)​

Myth Busters for Patients and Families, Fragile X Syndrome (PDF)​​



The content on this page was supported by the Cooperative Agreement Number 5 U38 OT000167, funded by the Centers for Disease Control and Prevention. Its contents are solely the responsibility of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention or the Department of Health and Human Services.