Incidence of down syndrome in mentally retarded people of north coastal andhra pradesh

Background: Mental Retardation (MR) (also called mental handicap) is a term for a pattern of persistently slow learning of basic motor and language skills (“milestones”) during childhood, and a significantly below normal global intellectual capacity as an adult. Down syndrome is the most first and common genetic cause of mental retardation. The aim of the present study was to estimate the frequency of Down syndrome in mentally retarded people of North Coastal Andhra Pradesh. Methods: This study was carried out an approximately on 100 mentally retarded children from North Coastal Andhra Pradesh and a control group consists of 100 normal individuals of same age group. The blood sample was collected from mentally retarded children and controls for the evaluation of the chromosomal abnormalities. The karyotype of all mentally retarded cases were assessed by conventional cytogenetic techniques (GTG –banding). Results: Out of 100 mentally retarded people analyzed, 88 (88%) had normal karyotype and remaining 12 (12%) were Down syndrome. Among them regular free trisomy constituted 8 (8%) cases, Robertsonian translocations in 2(2%) cases and mosaicism was recorded in 2 (2%) cases. Conclusions: The study confirmed the findings of earlier studies carried out in India and other countries. It emphasizes free trisomy 21 was found to be the most frequent autosomal aberration of Down syndrome when compared with Robertsonian translocations and mosaics.