Five Things You May Not Know About Fragile X Syndrome

Fragile X syndrome (FXS) is a genetic disorder. Because of changes in their genetic material (specifically the FMR1 gene), people who have FXS do not make a protein called FMRP, which is needed for normal brain development. People who have other fragile X-associated disorders also have changes in the FMR1 gene, but usually make some of the FMRP protein.

Watch a video about the causes of fragile X syndromeexternal icon

Signs and symptoms of FXS include:

  • Developmental delays (not sitting, walking, or talking at the same time as other children the same age);
  • Learning disabilities (trouble learning new skills); and
  • Social and behavior problems (such as not making eye contact, anxiety (fear, worry), trouble paying attention, hand flapping, acting and speaking without thinking, and being very active).

Having FXS is associated with an increased chance of intellectual disability, particularly in males, and of having autism spectrum disorder (ASD).

As part of CDC’s work to educate people about the condition and to celebrate fragile X awareness month, here are five things you may not know about FXS.

#1 FXS is genetic but there isn’t always a family history.

X genes

FXS means that a particular part of person’s FMR1 gene is much larger than usual. This part of the FMR1 gene ranges in size from person to person and can become bigger from one generation to the next. Therefore, many people with FXS have no family members with FXS symptoms. In some people who do not have FXS, this part of the FMR1 gene is a little larger than usual. These people are said to have a “premutation” in the FMR1 gene. FMR1 premutations run in families, and women with a premutation may give birth to children with FXS. Some people with a premutation have symptoms of fragile X-associated disorders, such as tremors and, in women, early menopause, although these symptoms are most commonly due to other causes.

#2 Babies aren’t routinely tested for FXS so families might not find out about FXS for a few years.

FXS requires a special blood test that is not usually included in the genetic tests that a pregnant woman gets or in the tests that are routinely 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.” The American Academy of Pediatrics recommendspdf iconexternal icon that children diagnosed with general developmental delays, intellectual disability, or autism spectrum disorder receive a genetic test for FXS.

#3 Not everyone who has FXS has the same symptoms, and FXS doesn’t just affect boys.

Both boys and girls can have FXS. FXS is more common in boys, and the symptoms are usually more severe in boys than in girls. Boys with FXS usually have some degree of intellectual disability, whereas girls range from normal intelligence to having an intellectual disability. But both boys and girls can have symptoms that range from mild to severe.

#4 There is no cure for FXS, but an early diagnosis can still help.

Even though there is no cure for FXS, there are educational, behavioral, and therapeutic services which can help. A diagnosis may also help families with family planning and connecting with support groups of other families affected by FXS. Learn more.

#5 CDC works with researchers and the fragile X community to improve the lives of people with the condition and their families.

To help individuals and families affected by FXS, we need to learn more about other conditions that commonly occur with FXS, the day-to-day lives of people living with FXS and their families, and the types of intervention and support that are most effective for individuals with FXS and their families.

Kids sitting on a haystack

CDC activities include:

  • Supporting the National Fragile X Foundation to develop the Fragile X Online Registry With Accessible Research Database (FORWARDexternal icon). Because FXS is a rare disorder—meaning that there are fewer than 200,000 newly identified cases per year in the United States—researchers who want to learn more may have difficulty finding enough affected individuals to get answers to scientific questions. The FORWARD database now includes carefully collected clinical, demographic, and behavioral information on more than 1,700 children and adults with FXS enrolled at fragile X specialty clinics throughout the United States.The information in the FORWARD database can be used to better understand many of the unanswered questions about FXS, and to find ways to improve the health and quality of life of people with FXS and their relatives and caregivers. Recent studies published in medical and scientific journals have used information from FORWARD to help answer questions that are important to individuals with FXS and their families (for example, what medications are most typically used to treat children with FXS with challenging behaviors such as irritability, agitation, aggression, and self-injury, and what to expect with toilet training efforts in children with FXS). Learn more about research studies using the FORWARD databaseexternal icon.
  • Working to learn more about how children with FXS develop compared to children with other conditions, including autism spectrum disorder (ASD) and developmental disability, and to learn more about children with FXS who have also been diagnosed with ASD or other conditions. CDC does this by looking at information about children that is being collected in the FORWARD study and comparing it to similar information about children with ASD and other developmental disorders that is being collected in another CDC-funded study called Study to Explore Early Development (SEED).
  • Collaborating with the American Academy of Pediatrics to develop and distribute educational materials to healthcare professionals and families. These materials are designed to raise awareness of FXS and encourage early diagnosis so that people with FXS can receive appropriate care and services. Learn more.
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