Plasma beta-amyloid levels are significantly associated with a transition toward Alzheimer's disease as measured by cognitive decline and change in neocortical amyloid burden

Background: We evaluated the utility of longitudinal measures of plasma amyloid- (A) as a means to identify pre-symptomatic cognitive decline in Alzheimer’s disease (AD) when coupled to neuroimaging and neuropsychological parameters. Methods: Participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study were grouped based upon cognitive change and changes in measurable levels of neocortical amyloid over 36 months. Participants were classified as those who transitioned for cognitive decline and change in neocortical amyloid, those healthy controls that did not transition, and stable AD participants over 36 months. Results: Comparisons of plasma A levels between the transition and non-transitional groups showed A1-42 and the A1-42/A1-40 ratio were significantly decreased at baseline (p = 0.008 and p = 0.002, respectively) and at 18 months (p = 0.003