Healthcare Providers: Top 5 Things to Know About FXS

What to know

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 a gene called the fragile X messenger ribonucleoprotein 1 (FMR1) gene. Any child with unexplained developmental delay, intellectual disability, and/or autism spectrum disorder should receive genetic testing for FXS. Healthcare professionals 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 healthcare providers assess comorbidities and associated conditions.

Doctor in hallway standing in front of other doctors

Top 5 things to know about FXS

Fact #1: There does not have to be a family history of FXS for a child to have the condition.‎

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.
family of 6 people smiling and looking at the camera
All children with FXS do not have a family history of FXS.

Fact #2: FXS cannot be diagnosed using a chromosome test or microarray.‎

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.
image of chromosome with orange tips
Fragile X syndrome is a genetic disorder caused by changes in a gene called FMR1.

Fact #3: Girls can have FXS, and boys with FXS are usually more severely affected.‎

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.
Kids playing tug of war outside
Both girls and boys can have FXS.

Fact #4: Not all FXS patients can be recognized by unusual physical characteristics. ‎

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.
enlarged ear with magnifying glass
Individuals with FXS may have dysmorphic features.

Fact #5: There is value in making a diagnosis of FXS even if there is no cure.‎

Although currently there is no cure for FXS, there are important supportive 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.
Male doctor meeting with mother and her daughter
A diagnosis of FXS can be helpful to the family because it can provide a reason for a child’s intellectual disabilities and behavior problems.
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See Also: AAP Myth Busters for Providers

The material in this PDF was adopted from AAP News © July 2016 American Academy of Pediatrics. FXS Myth Busters was created under Cooperative Agreement Number U38OT000167, 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.

What you can do as a healthcare provider

Ensure that all children with developmental delay, intellectual disability and/or autism spectrum disorder are considered for a genetic evaluation.123

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 females on the maternal side.
  • A history of early menopause or fertility problems on the maternal side.

Resources for healthcare professionals

CDC works with partners to provide resources for healthcare professionals to support the diagnosis and evaluation of patients who have or may have fragile X syndrome:

National Fragile X Foundation

American Academy of Pediatrics

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Content Source:
National Center on Birth Defects and Developmental Disabilities
  1. Hersh JH, Saul RA; Committee on Genetics. Health supervision for children with fragile X syndrome. Pediatrics. 2011 May;127(5):994-1006.
  2. Moeschler JB, Shevell M; Committee on Genetics. Comprehensive evaluation of the child with intellectual disability or global developmental delays. Pediatrics. 2014 Sep;134(3):e903-18.
  3. Saul RA. Genetic and genomic literacy in pediatric primary care. Pediatrics. 2013 Dec;132(Suppl 3):S198-202.