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Fragile X syndrome

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Other Names for this Disease

  • Fra(X) syndrome
  • FraX syndrome
  • FRAXA syndrome
  • FXS
  • Marker X syndrome
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Overview

What is fragile X syndrome?

What are the signs and symptoms of fragile X syndrome?

What causes fragile X syndrome?

How is fragile X syndrome inherited?

Is genetic testing available for fragile X syndrome?

How might fragile X syndrome be treated?

What is the long-term outlook for people with fragile X syndrome?

What is fragile X syndrome?

Fragile X syndrome is a genetic condition involving changes in part of the X chromosome.[1] This condition causes a range of developmental problems including learning disabilities and cognitive impairment.[2] It is the most common form of inherited intellectual disability in males and a significant cause of intellectual disability in females.[1] Other signs and symptoms may include symptoms of autism spectrum disorders, seizures, and characteristic physical features.[2] Fragile X syndrome is caused by a change (mutation) in the FMR1 gene and is inherited in an X-linked dominant manner.[1][2]
Last updated: 1/29/2015

What are the signs and symptoms of fragile X syndrome?

Fragile X syndrome is characterized by developmental problems including intellectual disability and delayed speech and language development. Males are usually more severely affected than females. Additional features may include anxiety; attention deficit disorder (ADD); features of autism spectrum disorders that affect communication and social interaction; and seizures. Most males and some females with fragile X syndrome have characteristic physical features that become more apparent with age. These features may include a long and narrow face; large ears; a prominent jaw and forehead; unusually flexible fingers; flat feet; and in males, enlarged testicles (macroorchidism) after puberty.[2]
Last updated: 1/29/2015

What causes fragile X syndrome?

Mutations (changes) in the FMR1 gene cause fragile X syndrome (FXS). This gene carries instructions to make a protein called the fragile X mental retardation 1 protein. The FMR1 gene contains a section of DNA called a CGG triplet repeat, which normally repeats from 5 to around 40 times. In most cases of FXS, this section of DNA is repeated more than 200 times, which "turns off" the FMR1 gene and disrupts the function of the nervous system. In a small portion of cases, other types of changes in the FMR1 gene cause FXS. These changes may involve a deletion of all or part of the gene, or a change in the building blocks (amino acids) used to make the gene's protein.[3]

People with 55 to 200 repeats of the CGG segment are said to have an FMR1 premutation. Most people with a premutation are intellectually normal. In some cases, people with a premutation have lower levels of the gene's protein and may have some mild symptoms of FXS. About 20% of women with a premutation have premature ovarian failure, and some people with a premutation have an increased risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS).[3]
Last updated: 1/29/2015

How is fragile X syndrome inherited?

Fragile X syndrome (FXS) is inherited in an X-linked dominant manner. A condition is X-linked if the responsible gene is located on the X chromosome. The inheritance is dominant if having only one changed (mutated) copy of the responsible gene is enough to cause symptoms of the condition.

In women who carry an FMR1 gene premutation (approximately 55 to 200 CGG repeats), the repeats can expand to more than 200 repeats in their cells that develop into eggs. This means that women with a premutation (or a full mutation) have an increased risk to have a child with FXS. The size of the risk corresponds to the number of CGG repeats they have.[4] By contrast, men with premutations are not at risk for the repeats expanding to over 200 when passing the gene to offspring.[3][4] However, men with a premutation will pass the premutation on to all of their daughters and none of their sons.[4] This is because boys receive only a Y chromosome from their fathers.[3]
Last updated: 1/29/2015

Is genetic testing available for fragile X syndrome?

Yes, genetic testing is available for fragile X syndrome. Carrier testing for at-risk relatives and prenatal testing for pregnancies at increased risk are possible if the diagnosis of an FMR1-related disorder (including fragile X syndrome) has been confirmed in a family member.[5]

The Genetic Testing Registry (GTR) provides information about the labs that offer genetic testing for fragile X syndrome. The intended audience for the GTR is health care providers and researchers. People with questions about genetic testing should speak with a health care provider or genetics professional.
Last updated: 1/29/2015

How might fragile X syndrome be treated?

There is no specific treatment available for fragile X syndrome.  Management of this condition is generally supportive and may include:
  • recognizing the need for special education and avoiding excessive stimulation, which may help with behavioral problems
  • early educational intervention and special education that is tailored to specific learning difficulties; small class size, individual attention and avoidance of sudden change is often needed
  • medications for behavioral issues that affect social interaction
  • routine medical management of strabismus, ear infections, reflux, seizures, mitral valve prolapse, and/or high blood pressure.[6]
Last updated: 1/28/2015

What is the long-term outlook for people with fragile X syndrome?

Life expectancy for people with fragile X syndrome is generally normal. Many affected people participate in an active lifestyle and have good health. Some people are more prone to a number of medical problems, such as ear infections and/or seizures. Regular medical checkups and awareness of increased health risks may improve the outlook for affected people.[7]
Last updated: 1/28/2015

References
  1. Haldeman-Englert C. Fragile X syndrome. MedlinePlus. 2007; http://www.nlm.nih.gov/medlineplus/ency/article/001668.htm. Accessed 4/20/2009.
  2. Fragile X syndrome. Genetics Home Reference. April 2012; http://www.ghr.nlm.nih.gov/condition/fragile-x-syndrome.
  3. Fragile X syndrome. Genetics Home Reference. May 2007; http://ghr.nlm.nih.gov/condition/fragile-x-syndrome. Accessed 6/15/2011.
  4. What Does it Mean to be a Carrier?. The National Fragile X Foundation. September 30, 2008; http://www.fragilex.org/html/carriers.htm. Accessed 6/15/2011.
  5. Robert A Saul, Jack C Tarleton. FMR1-Related Disorders. GeneReviews. October 28, 2010; http://www.ncbi.nlm.nih.gov/books/NBK1384/. Accessed 6/16/2011.
  6. Robert A Saul and Jack C Tarleton. FMR1-Related Disorders. GeneReviews. April 26, 2012; http://www.ncbi.nlm.nih.gov/books/NBK1384/.
  7. Treatments. Fragile X Research Foundation of Canada. 2009; http://www.fragilexcanada.ca/index.php?home&lng=en.


Other Names for this Disease
  • Fra(X) syndrome
  • FraX syndrome
  • FRAXA syndrome
  • FXS
  • Marker X syndrome
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.