Fragile X Syndrome is the most common inherited form of mental retardation among all racial and ethnic groups. It is so named, because in patients with this syndrome, the X chromosome appears to be physically constricted at a point, giving it a fragile appearance. The disease affects boys more severely than girls. Affected patients display mental impairment, ranging from learning disabilities to mental retardation, attention deficit and hyperactivity, anxiety, and occasional seizures. DNA testing for detection of Fragile X Syndrome has been available since 1992.
Fragile X syndrome is generally associated with a fragile site at Xq 27.3, which can be observed in the metaphase chromosome following selective culture conditions. At the molecular level, the fragile X syndrome is associated with an amplification of CGG repeat sequence of the FMR1 gene.