Fragile X Syndrome

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Fragile X Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • fragile site, folic acid type, rare, Fra(X)(Q27.3)
  • fragile X mental retardation protein, FMRP
  • fragile X mental retardation syndrome
  • marker X syndrome
  • Martin-Bell syndrome
  • mental retardation, X-linked, associated with Mar Xq28
  • X-linked mental retardation and macroorchidism

Disorder Subdivisions

  • None

General Discussion

Fragile X syndrome is characterized by moderate intellectual disability in affected males and mild intellectual disability in affected females. Distinctive physical features are sometimes present in affected males including a large head, long face, prominent forehead and chin, protruding ears, loose joints and large testes, but these features develop over time and may not be obvious until puberty. Motor and language delays are usually present but also become more apparent over time. Behavioral abnormalities including autistic behaviors are common.

Fragile X syndrome is caused by an abnormality (mutation) in the FMR1 gene. Affected individuals have an increased number of copies of a portion of the gene called CGG repeats. The greater the number of copies of CGG, the more likely there will be increased severity of the disorder. Fragile X syndrome occurs more often in males and results in more severe disease in males.

Mutations in the FMR1 gene are associated with two other conditions in addition to the fragile X syndrome (FXTAS and POI) and these conditions have been termed FMR1-Related Disorders. (See the Related Disorders section of this report for brief summaries of the other disorders.)

Supporting Organizations

FRAXA Research Foundation

10 Prince Place
Newburyport, MA 1950
Tel: (978)462-1866
Fax: (978)463-9985

Fragile X Society

Road End House
6 Stortford Road
Essex, CM6 1DA
United Kingdom
Tel: 4401371875100

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)251-4925
Fax: (301)251-4911
Tel: (888)205-2311

Let Them Hear Foundation

1900 University Avenue, Suite 101
East Palo Alto, CA 94303
Tel: (650)462-3174
Fax: (650)462-3144

Medical Home Portal

Dept. of Pediatrics
University of Utah
Salt Lake City, UT 84158
Tel: (801)587-9978
Fax: (801)581-3899

NIH/National Institute of Child Health and Human Development

31 Center Dr
Building 31, Room 2A32
Bethesda, MD 20892
Fax: (866)760-5947
Tel: (800)370-2943

NIH/National Institute on Aging

31 Center Drive, MSC 2292
Building 31
Bethesda, MD 20892
Tel: (301)496-1752
Fax: (301)496-1072
Tel: (800)222-2225

National Fragile X Foundation

1615 Bonanza St
Suite 202
Walnut Creek, CA 94596
Tel: (925)938-9300
Fax: (925)938-9315
Tel: (800)688-8765

New Horizons Un-Limited, Inc.

811 East Wisconsin Ave
P.O. Box 510034
Milwaukee, WI 53203
Tel: (414)299-0124
Fax: (414)347-1977

New York State Office for People with Developmental Disabilities

44 Holland Avenue
Albany, NY 12229
Tel: (866)946-9733

The Arc

1825 K Street NW, Suite 1200
Washington, DC 20006
Tel: (202)534-3700
Fax: (202)534-3731
Tel: (800)433-5255

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). A copy of the complete report can be downloaded free from the NORD website for registered users. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational therapies (if available), and references from medical literature. For a full-text version of this topic, go to and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only. NORD recommends that affected individuals seek the advice or counsel of their own personal physicians.

It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report

This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

For additional information and assistance about rare disorders, please contact the National Organization for Rare Disorders at P.O. Box 1968, Danbury, CT 06813-1968; phone (203) 744-0100; web site or email

Last Updated:  1/3/1970
Copyright  2010 National Organization for Rare Disorders, Inc.

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Fragile X Syndrome