Neuronal loss and beta-amyloid removal in the amygdala of people with Downsyndrome

The decrease in the number of neurons free of neurofibrillary changes, neur ons with neurofibrillary degeneration, and the total volume of beta-amyloid (A beta) deposits in the amygdala of people with Down syndrome and in late stages of Alzheimer disease were estimated by using morphometry and regres sion analysis. This model predicts that the duration of neurofibrillary cha nges from the pretangle stage to ghost tangles is approximately 4.7 years. The correlation between the decrease in the number of neurons and the decre ase in the amount of A beta indicates that amyloid deposition is associated with neurons and that loss of neurons causes decrease in A beta deposition . The presence of neurons only with neurofibrillary tangles, and the absenc e of the amyloid deposit predicted by regression analysis suggest that neur ons with tangles are not engaged in amyloid deposition. The disappearance o f amyloid by approximately 2.2 years after loss of neurons free of neurofib rillary changes indicates that A beta deposits are degradable and removable and that even in severely atrophic amygdala, there are mechanisms of amylo id resolution. This study shows that in normal aging in the amygdala, extra cellular A beta appears later than neurofibrillary changes. (C) 1999 Elsevi er Science Inc. All rights reserved.