Fragile X syndrome

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Martin-Bell syndrome; Marker X syndrome

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

Family members who have fewer repeats in the FMR1 gene may not have mental retardation, but may have other problems. Women with less severe changes may have premature menopause or difficulty becoming pregnant. Both men and women may have problems with tremors and poor coordination.

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 FMR1 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 who have reached puberty may 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.

Review Date: 04/30/2005
Reviewed By: Neal Sondheimer, M.D., PhD., Division of Genetics and Metabolism, Children's Hospital of Philadelphia, Philadelphia, PA. Review provided by VeriMed Healthcare Network.