This critical review examines mental retardation (MR) from a neuropsychological perspective. Competing definitions of MR are discussed and the prevalence is estimated. Descriptions are given of idiopathic MR and the five major identifiable prenatal causes of MR: fetal alcohol syndrome, Down's syndrome, fragile X syndrome, Prader-Willi syndrome, and Angelman syndrome. Similarities and differences among syndromes are examined. Cognitive deficits common to all disorders were in attention, short-term memory, and sequential information processing, whereas language and visuospatial abilities were varied. Neuroanatomical abnormalities common to all disorders were in the hippocampus and cerebellum; individual disorders typically showed a unique pattern of other neurological abnormalities. Both knowledge of individual MR-related disorders and comparative research between disorders are important for researchers and clinicians. Further research is called for in both areas. (JINS, 1996, 2, 159–176.)
