Do β-amyloid (Aβ) deposits in patients with Alzheimer's disease and Down's syndrome grow according to the log-normal model?

The size frequency distributions of diffuse, primitive and classic beta-amyloid (A beta) deposits were studied in single sections of cortical tissue from patients with Alzheimer's disease (AD) and Down's syndrome (DS) and compared with those predicted by the log-normal model. In a sample of brain regions, these size distributions were compared with those obtained by serial reconstruction through the tissue and the data used to adjust the size distributions obtained in single sections. The adjusted size distributions of the diffuse, primitive and classic, deposits deviated significantly from a log-normal model in AD and DS, the greatest deviations from the model being observed in AD. More A beta deposits were observed close to the mean and fewer in the larger size classes than predicted by the model. Hence, the growth of A beta deposits in AD and DS does not strictly follow the lognormal model, deposits growing to within a more restricted size range than predicted. However, A beta deposits grow to a larger size in DS compared with AD which may reflect differences in the mechanism of A beta formation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.