Mental retardation is a common and distressing disorder that affects 3% of the population. It is a clinically and etiologically heterogeneous group of conditions. It is among one of the major disorders that are still poorly understood in terms of etiopathogenesis and for which very little therapeutic help is provided. Poor understanding of its origins hampers the provision of effective treatment and preventive regimens therefore mental retardation remains a major challenge for medical practice.It could be due to combination of genetic and environmental factors. As Fragile X is the biggest...