Prospective study of the prevalence of Alzheimer-type dementia in institutionalized individuals with Down syndrome.

Institutionalized patients with Down syndrome (n = 307) were monitored for 5 to 10 years prospectively to determine prevalence of Alzheimer-type dementia. Clinical signs, cognitive functioning, and EEGs were assessed. When possible, postmortem neuropathological examinations were conducted. Progressive mental and physical deterioration was found for 56 of the residents. Mean age at onset of dementia was 56 years. Prevalence increased from 11% between ages 40 and 49 to 77% between 60 and 69. All patients 70 and over had dementia. Neuropathological findings were consistent with clinical diagnosis. Use of a dementia checklist, cognitive skills inventory, and EEG reliably detected Alzheimer-type dementia at an early stage.