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Fragile X syndrome is a genetic abnormality in an X chromosome that leads to intellectual disability and behavioral disorders.
Fragile X syndrome is the most common inherited cause of intellectual disability. The symptoms of fragile X syndrome are caused by abnormalities in DNA on the X chromosome. It affects about 1/4000 males and 1/8000 females. Females with the disorder are typically less impaired than males. Fragile X is inherited in an X-linked pattern and does not always cause clinical symptoms.
Examination of the karyotype reveals a constriction at the end of the long arm of the X chromosome, followed by a thin strand of genetic material. The constriction and thin strand give the appearance of a fragile portion of the X chromosome. Sequencing of the genetic material reveals a repeating base pair triplet that is responsible for the syndrome.
Symptoms and Signs
People with fragile X syndrome have physical, cognitive and behavioral abnormalities. They have large, protuberant ears; a prominent chin and forehead; a high arched palate; and, in postpubertal males, macroorchidism. The joints may be hyperextensible, and heart disease (mitral valve prolapse) may occur. Cognitive abnormalities may include mild to moderate intellectual disability. Features of autism may develop, including perseverative speech and behavior, poor eye contact, and social anxiety. Women may experience menopause in their mid-30s.
Diagnosis
Fragile X syndrome is frequently not suspected until school age or adolescence, depending on the severity of the symptoms. Boys with autism and intellectual disability should be tested for fragile X syndrome. DNA testing can detect abnormal DNA on the fragile X chromosome. The greater the number of abnormal repetitions of DNA found, the more likely the child will have symptoms.
Treatment
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
Content last modified December 2008
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