Fragile X is a genetic disorder that is the most common known cause of inherited mental impairment in humans.

Fragile X occurs when a person doesn't make any or doesn't make enough of a certain protein, called Fragile X Mental Retardation Protein (FMRP).

The absence or insufficiency of this protein is what causes the various characteristics that we see in people with Fragile X. Fragile X tends to be worse in males than in females because it is a sex-linked trait that is carried only on the X chromosome. Since males inherit an X and a Y chromosome, if they inherit Fragile X on their one X chromosome, then they do not produce any of the protein FMRP, because the Y chromosome does not carry the gene that encodes for FMRP. Since females inherit two X chromosomes (XX), they have an extra, or redundant, source of FMRP. If a female inherits Fragile X on one of her X chromosomes, she probably inherited a normal gene on her other X-chromosome, and so she can still produce some FMRP although she probably produces an insufficient amount.

Therefore, males with Fragile X tend to have more severe symptoms than females with Fragile X, except for in the case where a female inherits two X chromosomes with Fragile X, one from each parent. This case only occurs when both of a persons parents have Fragile X.<./p>

We know that FMRP is synthesized primarily in the brain and (in males) in the testicles. These two organs are locations that are most affected by Fragile X, through mental retardation and macroorchidism (enlarged testicles). Other organs, such as the liver, lung, kidney, spinal cord, and gastrointestinal tract, also synthesize FMRP but don't appear to be heavily affected by Fragile X. It is not known exactly what the role of FMRP is, but it is clear that FMRP is not a protein that is absolutely necessary for survival. If that were the case, every individual lacking the ability to synthesize FMRP would not survive. Although most people with Fragile X can survive, the syndrome is thought to affect their quality of life.

There are many interventions and medical treatments available for the various symptoms that affected individuals experience. Since the symptoms of Fragile X are very diverse and differ greatly from person to person, the appropriate treatments are also highly diverse and varied. It is therefore very important that any person with Fragile X is seen by a professional who is familiar with this disorder and who can recommend a specific set of tailored treatments for that individuals needs.

Here is a useful website on Fragile X:
X Fragile Syndrome