Abstract
To the Editor: Alzheimer's disease is characterized by the presence of numerous senile plaques within the neocortex, hippocampus, and amygdala and by neurofibrillary degeneration (tangles) and loss of neurons within these areas and within subcortical regions such as the nucleus basalis of Meynert, locus ceruleus, and dorsal raphe.1 Nearly all persons with Down's syndrome who live past 50 years of age also have plaques and tangles within their brains that are broadly similar in form, number, and distribution to those seen in Alzheimer's disease2 , 3; such changes are seen only rarely in patients under 20 years of age.3 , 4 Hence, in . . .