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Fragile X Syndrome Facts for Families

What to know

Fragile X syndrome (FXS) is caused by a change in the genetic material in each cell of the body. This change in genetic material makes it hard for cells to produce a protein that is necessary for normal brain development and normal brain function. As an inherited condition, FXS, or the risk for developing FXS, can be passed on to the next generation.

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5 Facts to Know About FXS

Graphic of a DNA sequence.
Fragile X syndrome is a genetic disorder caused by changes in a gene called FMR1.

Fact #1: Children are not usually tested for FXS when women are pregnant with them, or right after they are born.‎

FXS requires a special blood test that is not usually included in the genetic tests that a pregnant woman gets or in the tests done right after a baby is born. The only way to diagnose FXS is with a special blood test called the "FMR1 DNA Test for Fragile X."
Kids playing tug of war outside
Both girls and boys can have FXS.

Fact #2: Girls and boys can have FXS. However, boys with FXS are usually more severely affected.‎

Both boys and girls can have FXS. The symptoms are usually more severe in boys than in girls, but both boys and girls can have symptoms that range from mild to severe.
enlarged ear with magnifying glass
Individuals with FXS may have dysmorphic features.

Fact #3: Some people with FXS can have large ears or a long, narrow face.‎

Many people with FXS do not have certain physical traits that textbooks attribute to FXS. However, some people with FXS do have some of these physical features. These features can be seen in younger children, but some may not show up until puberty.
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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Fact #4: Even though there is no cure for FXS, a diagnosis can still be helpful.
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Even though there is no cure for FXS, there are educational, behavioral, and therapeutic services that can help. A diagnosis may also help families with family planning and connecting with support groups of other families affected by FXS.
Family tree animated with icons of people within the tree
All children with FXS do not have a family history of FXS.

Fact #5: A child can have FXS without having a family history of FXS.‎

FXS is caused by a change in genetic material that ranges in size and can become bigger from one generation to the next. Small size changes typically do not cause FXS, but large size changes often do cause FXS. Therefore, a person can have FXS without a family history if that person inherits a large change in the size of the genetic material while everyone else in the family has small size changes. Families that do not have FXS but have small size changes can have other signs that FXS could occur in future generations. These families have members who may have fragile X-associated disorder symptoms, such as tremors and early menopause, which could be identified through a more thorough evaluation of family history.

The FXS facts listed on this page are 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 to do if you think your child may have FXS

Currently, there is no cure for FXS, but an early diagnosis can help a family get treatment and services for their child sooner. Having a diagnosis may provide valuable information for other family members as well.

Talk to your child's healthcare provider.

  • Talk to your child's healthcare provider about genetic testing if your child is not sitting, walking, or talking at the same time as other children the same age; has trouble learning new skills; or has social and behavioral problems such as not making eye contact, anxiety, trouble paying attention, hand flapping, acting and speaking without thinking, and being very active.

Find out about your family history.

  • Talk to your family to see if anyone remembers a history of Parkinson-like tremors in older men on the mother's side of the family, or a history of early menopause or fertility problems in women on the mother's side of the family. These are symptoms of fragile X-associated disorders, which suggest that FXS could run in the family.

What to do if your child has been diagnosed with FXS

  • Early intervention services in each state help children from birth to 3 years old learn important skills. You can ask to have your child evaluated, and these services may improve your child's development. Even if your child has not been diagnosed with FXS, they may still be eligible for services.
  • Work with your child's pediatrician to get care and services for your child.
  • Contact the organizations that work with FXS families and become familiar with FXS resources.
  • Consider joining a local group of FXS families to share information and support each other.

Center for Parent Information and Resources‎

For information about services in your state, you can access your state's parent center.



Find Your Parent Center

Resources for Patients and Families Living with FXS

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Content Source:
National Center on Birth Defects and Developmental Disabilities