MAPT and Alzheimer disease: Prior studies have also shown that Aβ42/Aβ40 can predict amyloid burden12 and plasma p-tau can predict neuropathology in AD.14,15 In addition to its association to risk of AD16 and AD pathology,17 GFAP had been shown to associate with vascular pathology.18,19 A combination of one or more of these AD-related plasma biomarkers has been shown to predict cognitive decline.20-22 Nonetheless, unaddressed questions remain, such as, how does the variance explained by plasma biomarkers compare with the variance captured by imaging and non-imaging measures when predicting cognitive decline?