MedlinePlus Medical Encyclopedia: Fragile X syndrome

Skip navigation


Medical Encyclopedia
Other encyclopedia topics:	A-Ag Ah-Ap Aq-Az B-Bk Bl-Bz C-Cg Ch-Co Cp-Cz D-Di Dj-Dz E-Ep Eq-Ez F G H-Hf Hg-Hz I-In Io-Iz J K L-Ln Lo-Lz M-Mf Mg-Mz N O P-Pl Pm-Pz Q R S-Sh Si-Sp Sq-Sz T-Tn To-Tz U V W X Y Z 0-9

Fragile X syndrome

Contents of this page:
Alternative names Definition Causes, incidence, and risk factors Symptoms Signs and tests Treatment	Support Groups Expectations (prognosis) Complications Calling your health care provider Prevention

Alternative names

Martin-Bell syndrome; Marker X syndrome

Definition Return to top

Fragile X syndrome is a genetic condition involving changes in the long arm of the X chromosome. It is characterized by mental retardation.

Causes, incidence, and risk factors Return to top

Fragile X syndrome is the most common form of inherited mental retardation in males and a significant cause in females. The inheritance is different from common dominant or recessive inheritance patterns. A fragile area on the X chromosome tends to repeat bits of the genetic code. The more repeats, the more likely there is to be a problem. Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is more likely to affect them more severely.

Symptoms Return to top

Family history of fragile X syndrome, especially a male relative
Mental retardation
Large testicles (macro-orchidism)
Large size
Tendency to avoid eye contact
Hyperactive behavior
Large forehead and/or ears with a prominent jaw

Signs and tests Return to top

A specific genetic test (PCR) can now be performed to diagnose this disease. This test looks for an expanded mutation (called a triplet repeat) in the FRAXA gene. Formerly a specific type of chromosome analysis was done and this may still be available.

There are very few outward signs of Fragile X syndrome in babies but one is a tendency to have large head circumference. Measurement of oversized testes in males can also suggest the diagnosis. An experienced geneticist may note subtle differences in facial characteristics. Mental retardation is the hallmark of this condition and, in females, this may be the only sign of the problem.

Treatment Return to top

There is no specific treatment for Fragile X syndrome. Instead, effort is directed toward training and education so that affected children can function at as high a level as is possible. Because the condition is not rare, specific educational approaches have been developed and tested.

Support Groups Return to top

National Fragile X Foundation
www.nfxf.org
800-688-8765

Expectations (prognosis) Return to top

The outcome depends on the extent of mental retardation.

Complications Return to top

Complications vary depending on the type and severity of symptoms.

Calling your health care provider Return to top

Call your health care provider if you suspect the possibility of Fragile X syndrome in a child with mental retardation.

Prevention Return to top

Genetic counseling may help prospective parents with a family history of Fragile X syndrome. Genetic testing can help determine the level of risk in such a family.

Update Date: 8/6/2003

Updated by: Douglas R. Stewart, M.D., Division of Medical Genetics, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.