Diseases & Conditions


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Fragile X Syndrome


Fragile X syndrome is a genetic abnormality in the X chromosome that leads to delayed development and other symptoms.

The symptoms of fragile X syndrome are caused by abnormalities in DNA on the X chromosome. Usually, affected boys inherit the genetic abnormality from their mothers.

Many children with the syndrome have normal intelligence. However, the syndrome is the most commonly diagnosed inherited cause of mental retardation among boys. The severity of symptoms, including mental retardation, is worse in boys than in girls with the disorder. This is because boys have only one X chromosome; the second X chromosome in girls helps compensate for the fragile X chromosome. Symptoms, which are often subtle, include delayed development; large, protuberant ears; a prominent chin and forehead; and, in boys, large testes (most apparent after puberty). The joints may be abnormally flexible, and heart disease (mitral valve prolapse) may occur. Features of autism may develop. Women may experience menopause in their mid 30s.

The presence of abnormal DNA on the fragile X chromosome can be detected by tests before or after birth.

Early intervention, including speech and language therapy and occupational therapy, can help children with fragile X syndrome to maximize their abilities. Stimulants, antidepressants, and antianxiety drugs may be beneficial for some children.

Last full review/revision December 2008 by Gregory S. Liptak, MD, MPH

Source: The Merck Manual Home Edition