A Comparison of β-Amyloid Deposition in the Medial Temporal Lobe in Sporadic Alzheimer's Disease, Down's Syndrome and Normal Elderly Brains

Abstract

The density of β-amyloid (Aβ) deposits was studied in the medial temporal lobe in non-demented individuals and in sporadic Alzheimer's disease (SAD) and Down's syndrome (DS). No Aβdeposits were recorded in six of the non-demented cases, while in a further eight cases, these were confined to either the lateral occipitotemporal or parahippocampal gyrus. The mean density of Aβ deposits in the cortex was greater in SAD and DS than in non-demented cases but with overlap between patient groups. The mean density of Aβ deposits was greater in DS than SAD consistent with a gene dosage effect. The ratio of primitive to diffuse Aβ deposits was greater in DS and in non-demented cases than in SAD and the ratio of classic to diffuse deposits was lowest in DS. In all groups, Aβ deposits occurred in clusters which were often regularly distributed. In the cortex, the dimension of the Aβ clusters was greater in SAD than in the non-demented cases and DS. The data suggest that the development of Aβ pathology in the hippocampus could be a factor in the development of DS and SAD. Furthermore, the high density of Aβ deposits, and in particular the high proportion of primitive type deposits, may be important in DS while the development of large clusters of Aβ deposits may be a factor in SAD.