A mental disorder characterized by arrested or incomplete mental development, with onset before age 18, leading to significantly below-average intellectual functioning (specifically, IQ below 70), accompanied by deficits in adaptive functioning in such areas as interpersonal communication, self-care, home living, social skills, use of public amenities, self-direction, scholastic or academic performance, work, leisure, health, or safety. According to the World Health Organization, an IQ between 50 and 70 is approximately indicative of mild mental retardation, 35–50 moderate mental retardation, 20–35 severe mental retardation, and below 20 profound mental retardation. See cerebral gigantism, cerebral palsy, cretinism, cri du chat, Down's syndrome, foetal alcohol syndrome, fragile X syndrome, Hurler's syndrome, idiot savant, Klinefelter's syndrome, Lesch-Nyhan syndrome, macrocephaly, microcephaly, mild mental retardation, moderate mental retardation, phenylketonuria, profound mental retardation, severe mental retardation, Tay-Sachs disease, Williams syndrome, zombie (2). See also savant. Compare borderline intelligence. MR abbrev.
Subjects: Medicine and Health — Psychology.