Plasma Amyloid Beta-42 Independently Predicts Both Late-Onset Depression and Alzheimer Disease

Objectives: Depression in the elderly might represent a prodromal phase of Alzheimer disease (AD). High levels of plasma amyloid beta-42 (A beta 42) were found in prestages of AD and also in depressed patients in cross-sectional studies. This study examined the association of emerging late-onset depression (LOD) and AD with plasma A beta 42 in a sample of never depressed and not demented persons at baseline. Design: Prospective 5-year longitudinal study. Participants: A community dwelling of older adults (N = 331) from the Vienna Transdanube Aging study. Measurements: Laboratory measurements, cognitive functioning, and depressive symptoms were assessed at baseline, 2.5, and 5 years follow-ups. Results: After exclusion of converters to AD, regression analysis revealed that higher plasma A beta 42 at baseline was a positive predictor for conversion to first episode of LOD. Independent of whether persons with mild cognitive impairment (MCI) at 2.5 years were included or excluded into regressions, higher plasma A beta 42 at baseline was a significant predictor for the development of probable or possible AD at 5 years. Higher conversion to AD was also associated with male gender but not with either higher scores on the Geriatric Depression Scale (GDS), with stroke or cerebral infarction nor apolipoprotein E epsilon 4 allele. No association was found for an interaction between plasma A beta 42 levels and GDS. Conclusions: Higher plasma A beta 42 at baseline predicted the development of first episode of LOD and conversion to probable or possible AD. Emerging depression as measured by scores on GDS at the 2.5-year follow-up, either alone or as an interaction factor with plasma A beta 42, failed to predict the conversion to AD at 5 years. (Am J Geriatr Psychiatry 2010; 18: 973-982)