What causes of fragile x syndrome?

Gene mutation: Fragile x syndrome is due to a mutation within the fmr1 gene on x chromosome. Part of the gene gets repeated too many times. It is the most common genetic cause of intellectual disability. Please see: http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0002633/ and http://www.Fragilex.Org/ for more information.

Chromosome defect: Patients with fragile x have a defective x chromosome. There are several variants, and not all cells may be affected. It is full disease only in males, but females can be carriers. It is a genetic disorder, but it often just occurs without warning. Affected boys can vary from normal to severe retardation and autism. There is no cure.