Fragile X syndrome is caused by a "fragile" site at the end of the long arm of the X-chromosome and the genetic disorder manifests itself through a complex range of behavioural and cognitive phenotypes.

Fragile X syndrome is the result of genetic mutation which varies considerably in severity among patients and is the most common cause of inherited mental retardation. Although it is a X-linked recessive trait with variable expression and incomplete penetrance, 30 per cent of all carrier women are affected.

According to the Fragile X association of Southern California, Fragile X syndrome is the single most common inherited cause of mental impairment affecting 1 in 3600 males and 1 in 4000 to 6000 females with full mutation worldwide. Some studies also suggest that fragile X affects 1 in every 2000 males and 1 in every 4000 females of all races and ethnic groups.

Studies have also revealed that 1 in 259 women of all races carry fragile X and could pass it to their children. The number of men who are carriers is thought to be 1 in 800 of all races and ethnicity. Carrier females have a 30 to 40% chance of giving birth to a retarded male child and a 15 to 20 per cent chance of having a retarded female.

According to World Health Organization (WHO, the diagnosis of Fragile-X syndrome is made through the detection of errors in the FMR1 gene. Over 99 per cent of individuals have a full mutant FMR1 gene. Tests used for diagnosis include chromosome analysis and various protein tests.

Diagnosis is usually made when young, and there is no current cure for this illness. Early diagnosis of the syndrome call allow for therapeutic interventions like speech therapy, occupational therapy, psychotherapy and special education, that can considerably improve the quality of the patients' life.