Fragile X syndrome is a hereditary condition which causes a wide range of mental impairment, from mild learning disabilities to severe mental retardation. It is the most common cause of genetically-inherited mental impairment. In addition to mental impairment, fragile X syndrome is associated with a number of physical and behavioral characteristics.

There are several tests that can be done to determine if someone has fragile X syndrome and if family members have the potential to transmit the gene for fragile X syndrome.

The biological cause of fragile X and the pattern of transmission of the disease are complex. Fragile X syndrome affects individuals in a wide variety of ways. Some individuals experience significant challenges because of the effects of fragile X, while the impact on others is so minor that they will never be diagnosed.

Males and females exhibit quite different physical, cognitive, behavioral, sensory, speech and language impacts of fragile X syndrome. In general, females with fragile X either do not have the characteristics seen in males, or the characteristics show up in a milder form. The difference is probably due to the fact that females have two x-chromosomes instead of the one that males carry. As a result, females who have fragile X, have two sets of instructions for making FMRP (fragile X mental retardation protein), one that works and one that doesn't.

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