A condition of significantly below average intellectual development (IQ<70) and adaptive functioning in, for example, self-care, that is manifested before 18 years of age. An IQ between 50 and 70 is taken to signify mild mental retardation, 35 to 50 the moderate form, 20 to 35 the severe manifestation, and below 20 profound mental retardation. Mental retardation can occur with other signs and symptoms such as Down’s syndrome and Fragile X syndrome, while there can be no additional abnormalities. The terms ‘mentally retardation’ and ‘mentally retarded’ stem from over 50 years ago, and the term ‘intellectual disability’ tends to be preferred nowadays in English-speaking countries. In fact, in the States in October 2010, President Barack Obama signed a law decreeing that federal statutes can no longer refer to the term ‘mental retardation’, and it should be replaced by ‘intellectual disability’. The use of the former term is increasingly being regarded as derogatory and exclusive, and eventually becoming part of hate speech. What must not be forgotten is that mental retardation was a criterion for subjecting an individual to eugenics. It was still a practice used in Switzerland and Sweden until 1976.
See Disability, Down’s syndrome, Eugenics, Fragile X syndrome, Hypoxic-ischemic encephalitis, Intelligence, Learning disability, Neuronal migration disorders, Signs and symptoms