Fragile X syndrome screening of families with consanguineous and non-consanguineous parents in the Iranian population.

Fragile X syndrome is the most common form of inherited mental retardation (MR). It is caused by the expansion of CGG triplet repeats in the fragile X mental retardation 1 (FMR1) gene. In mentally retarded males, the frequency of fragile X syndrome is approximately 2-3 percent, but little is known about its proportion in mentally retarded patients from countries where parental consanguinity is common.