MAPT and Alzheimer disease: Briefly, Tau/Aβ42 ratios combine the two core biomarkers of the principal pathological processes, underlying AD into a single marker; combining measurements of two different proteins may compensate for natural fluctuations in the levels of each protein; and the temporal profile of Aβ42 and tau biomarkers differ, with Aβ42 considered to be an earlier metric of disease development than tau [35].