Summary of Fragile X Syndrome
From www.fragilex.org

Fragile X syndrome is the most common inherited cause of mental impairment. The syndrome occurs in approximately 1 in 3600 males and 1 in 4000 to 6000 females. Fragile X syndrome affects individuals in a wide variety of ways. Some individuals experience significant challenges 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.

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. Males with fragile X have only one X chromosome with its nonfunctioning FMR1 (fragile X mental retardation 1) gene. It appears that females are able to produce enough of the FMRP to fill most of the body's needs, but not all.

Inheritance
Fragile X in an "X-linked" condition, which means that the gene is on the X chromosome. Since a woman has two X chromosomes a woman with a premutation or full mutation has a 50% chance of passing on the X with the mutation in each pregnancy. In many X linked conditions only males who inherit the abnormal gene are affected, however in fragile X syndrome females can also be affected. Additionally, in other X linked conditions all males who carry the gene are affected, however in fragile X syndrome, unaffected males can carry the gene in the premutation form and have no symptoms of fragile X syndrome. Males with the premutation will pass it on to all of their daughters and none of their sons (they pass their Y chromosome on to their sons).

Treatment
At this time, there is no cure for fragile X syndrome. However, special education, speech and language therapy, occupational therapy and behavioral therapies are helpful in addressing many of the behavioral, and cognitive issues in fragile X syndrome.