WHAT DETERMINES THE SIZE FREQUENCY-DISTRIBUTION OF BETA-AMYLOID (A-BETA) DEPOSITS IN ALZHEIMERS-DISEASE PATIENTS

The factors determining the size of individual beta-amyloid (A beta) deposits and their size frequency distribution in tissue from Alzheimer's disease (AD) patients have not been established. In 23/25 cortical tissues from 10 AD patients, the frequency of A beta deposits declined exponentially with increasing size. In a random sample of 400 A beta deposits, 88% were closely associated with one or more neuronal cell bodies. The frequency distribution of A beta deposits which were associated with 0,1,2,...,n neuronal cell bodies deviated significantly from a Poisson distribution, suggesting a degree of clustering of the neuronal cell bodies. In addition, the frequency of A beta deposits declined exponentially as the number of associated neuronal cell bodies increased. A beta deposit area was positively correlated with the frequency of associated neuronal cell bodies, the degree of correlation being greater for pyramidal cells than smaller neurons. These data suggested: (1) the number of closely adjacent neuronal cell bodies which simultaneously secrete A beta was an important factor determining the size of an A beta deposit and (2) the exponential decline in larger A beta deposits reflects the low probability that larger numbers of adjacent neurons will secrete A beta simultaneously to form a deposit.