Identifying a biomarker for Alzheimer's disease that can be obtained from a blood sample has been a goal of researchers for many years. Over the past few years a number of investigators have studied several plasma biomarkers but most frequently plasma amyloid beta (Aβ)40 and Aβ42 while others have explored the use of genetic variants as biomarkers for diagnosis or risk. This review considers the cross-sectional and longitudinal data regarding plasma Aβ40 and Aβ42 as diagnostic biomarkers as well as risk biomarkers. Review of recent genome-wide association studies indicates as many as 10 genetic variants have been associated with susceptibility to Alzheimer's disease (AD). Further analysis suggests that these factors have modest effects on risk and are thus not helpful, as yet, in the diagnosis of disease. Until the function of these genes is understood, their role in risk and diagnosis will remain uncertain. Thus, there are several types of peripheral biomarkers under investigation, but more work is required before they can be deemed clinically useful.
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