Alzheimer-type neuropathology and clinical symptoms of dementia in mentally retarded people without Down syndrome.

Postmortem morphometric analyses of Bielschowsky stained sections from brains of 70 mentally retarded people without Down syndrome, age 65 and over when they died, indicated Alzheimer-type neuropathology in 22 cases (31%) and a majority with at least presence of some Alzheimer-type lesions. Based upon information abstracted from clinical histories, however, old-age-associated dementia proved to be difficult to judge reliably. Nevertheless, for otherwise healthy individuals (n = 25), loss of motor skills, development of problem behaviors, and a 10-point drop in IQ appeared to be likely indicators of Alzheimer's disease. Prevalence estimates of Alzheimer-type neuropathology among nonretarded people and the present sample appear comparable, and projections must be made to address the special needs of this rapidly growing population of retarded people.