Auditory P300 response in the assessment of Alzheimer's disease in Down's syndrome: a 2-year follow-up study.

Sixty-five subjects with Down's syndrome were followed up and retested 2 years after the initial recording of auditory P300 (P3) event-related potential described in a companion paper (Blackwood et al., 1988). The number of subjects showing clinical evidence for Alzheimer's type dementia had increased by a further 14%. In subjects showing clinical deterioration over a period of 2 years, 78% (7/9) had an increase in P3 latency which was three standard deviations or greater than the group mean. None of the 20 fragile-X group retested showed significant change after 2 years. The results suggest that P3 change may be a sensitive index of the onset of Alzheimer's type dementia in Down's syndrome.