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.

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 recommendsexternal 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..."
Fragile X Syndrome