Biomarkers for preclinical Alzheimer's disease.

Currently, there is a pressing need to shift the focus to accurate detection of the earliest phase of increasingly preclinical Alzheimer's disease (AD). Meanwhile, the growing recognition that the pathophysiological process of AD begins many years prior to clinically obvious symptoms and the concept of a presymptomatic or preclinical stage of AD are becoming more widely accepted. Advances in clinical identification of new measurements will be critical not only in the discovery of sensitive, specific, and reliable biomarkers of preclinical AD but also in the development of tests that will aid in the early detection and differential diagnosis of dementia and in monitoring disease progression. The goal of this review is to provide an overview of biomarkers for preclinical AD, with emphasis on neuroimaging and neurochemical biomarkers. We conclude with a discussion of emergent directions for AD biomarker research.