A COMPARISON OF BETA-AMYLOID (AP) DEPOSITION IN THE MEDIAL TEMPORAL-LOBE IN LATE-ONSET SPORADIC ALZHEIMERS-DISEASE, AND DOWNS-SYNDROME

The density of diffuse, primitive, classic and compact beta-amyloid (A beta) deposits was estimated in regions of the medial temporal lobe (MTL) in 15 cases of late-onset sporadic Alzheimer's disease (AD) and 12 cases of Down's syndrome (DS). A similar pattern of A beta deposition was observed in the MTL in the AD and DS cases with a reduced density of deposits in the hippocampus compared with the adjacent cortical regions. Total A beta deposit density was greater in DS than in AD in all brain regions examined. This could be attributable to overexpression of the amyloid precursor protein gene. The ratio of the primitive to the diffuse A beta deposits was greater in DS than in AD which suggests that the formation of mature amyloid deposits is enhanced in DS. The diffuse deposits exhibited a parabolic and the primitive deposits an inverted parabolic response with age in the DS cases. This suggests either that the diffuse and primitive deposits are sequentially related or that there are alternate pathways of A beta deposition.