Genetics of Mental Retardation

According to various estimates, mental retardation occurs in 1-3% of the population. Mental retardation is customary to clinically classify in terms of its severity; however, its classification still remains a challenge. Gene or chromosome abnormalities are responsible for 25 to 50% of mental retardation cases. Possible variants of genetically determined disorders are known as chromosomal, autosomal dominant, autosomal recessive, X-linked, and multifactorial ones. The specific cause of mental retardation cannot be clinically suspected in most cases. Until recently, this uncertainty has not allowed for target DNA diagnosis and the patients have remained without molecular diagnosis, and the families of these patients could not plan the birth of a healthy child. With the advent of a high-performance parallel sequencing technology, it has become possible to analyze not only individual mutations or genes, but whole exome and even genome for clinical and diagnostic purposes. The review considers the epidemiological, clinical, and genetic aspects of the heterogeneity of mental retardation. It gives calculations of the number of genes, defects of which are associated with mental retardation and shows prospects for its diagnosis using the new high-performance diagnostic techniques.