It is a generalized disorder, characterized by sub average cognitive functioning and deficits in two or more adaptive behaviors with onset before the age of 18. Once focused almost entirely on cognition, the definition now includes both a component relating to mental functioning and one relating to individuals' functional skills in their environment.
Mental Retardation is a particular state of functioning that begins in childhood and is characterized by limitations in intelligence and adaptive skills. Mental retardation reflects the “fit” between the capabilities of an individual and the structure of the environment.
