Mental retardation: a new challenge

Abstract

Although the care of the mentally handicapped in the RSA has improved over the past decades, it has only recently been possible to accurately establish the causes of mental retardation (MR). According to the WHO, the average incidence of severe MR (IQ < 50) is approximately 3-4 per 1 000 of the general population, while mild MR (IQ 50-70) occurs in about 20-30 individuals per 1 000 of the population. Genetic diagnostic investigations by the Genetic Services Division of the Department of National Health and Population Development have shown that the causes of serious MR at a school for white mentally retarded individuals can be divided as: genetic: 46%; non-genetic: 17%; and unknown causes: 37%. Chromosome abnormalities are the most important cause (± 18%) of MR, with Down syndrome and the Martin-Bell syndrome being the most common examples.