Understanding Fragile X Syndrome



Fragile X syndrome is a rare genetic disease that affects about 1 in 3,600 males and 1 in 6,000 females. Worldwide, fragile X syndrome is also the leading cause of inherited intellectual disability.

The symptoms of fragile X syndrome vary from person to person and range from mild learning disabilities to severe handicaps. People with fragile X syndrome typically display certain behavioral characteristics such as hyperactivity and autism, as well as noticeable physical features including flat feet, large ears, and/or a long face.

What Causes Fragile X Syndrome?

Fragile X syndrome occurs due to a mutation in the FMR1 gene. The FMR1 gene stops the body from making a protein called FMRP. FMRP helps to facilitate connections between brain cells and the nervous system. Without FMRP present, a developing brain sends inadequate signals, causing the developmental problems associated with fragile X syndrome.

The FMR1 gene sits on the X chromosome. Females have two copies of the X chromosome, so they also have two copies of the FMR1 gene. Males only have one X chromosome; If the one X chromosome doesn’t work how it should, there’s no backup. This is why males with fragile X syndrome tend to have more severe symptoms than females.

What is a Fragile X Carrier Test?

A fragile X carrier test is a genetic test used to determine a person’s carrier status. The test also provides insights about the risk of having a child with fragile X syndrome.

To perform a fragile X carrier test, your general practitioner or OB/GYN draws a sample of your blood. Results usually take about two weeks.

How is Fragile X Syndrome Inherited?

If you have an abnormal FMR1 gene, you’re also a fragile X carrier. However, being a fragile X carrier doesn’t necessarily mean you’ll have any obvious signs or symptoms.

The risk of having a child with fragile X syndrome depends on several factors. For example:

  • Women who are fragile X carriers have up to a 50% chance of having a child with fragile X syndrome
  • Men who are fragile X carriers will pass the gene onto all of their daughters but none of their sons
  • Daughters of men who are fragile X carriers are usually healthy, but risk having offspring with fragile X syndrome

If you have a family history of fragile X syndrome or you’re concerned about your risk of being a carrier for fragile X syndrome, talk with your general practitioner or OB/GYN about genetic screening.

Will I know it if I’m a Fragile X Carrier?

Fragile X syndrome affects people of all racial groups and ethnic backgrounds. In addition, research suggests that about 1 in every 250 women carries the abnormal version of the FMR1 gene that causes fragile X syndrome.

That said, there are certain factors that may increase the risk of having a child with fragile X syndrome, including:

  • A family history of fragile X syndrome
  • Infertility problems associated with premature ovarian failure (POF)
  • A family history of intellectual disability or autism of unknown cause
  • A family history of adult-onset ataxia

What Can I Do if I Have a Gene for Fragile X Syndrome?

Learning you’re a carrier of fragile X syndrome can generate many questions in the minds of expecting parents. Many babies born with fragile X syndrome experience learning disabilities and handicaps.

A general practitioner or OB/GYN can refer you to a genetic counselor who can explain the results of your screening test. Resources from the National Fragile X Foundation or the FRAXA Research Foundation can also help you better understand what Fragile X is, and what it may mean for your family.

Sources:

https://www.ucsfhealth.org/education/carrier-testing-for-fragile-x-syndrome#3

https://www.cdc.gov/ncbddd/fxs/inherited.html

https://www.cdc.gov/ncbddd/fxs/facts.html

https://rarediseases.org/rare-diseases/fragile-x-syndrome/

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