APOE and Alzheimer disease: Regional expression levels were correlated between each RAD DEP and each of four proteins thought to be central to either the etiology or pathogenesis of AD: Aβ, APOE, and TAU as well as the TAU-195 peptide (SGYSSPGSPGTPGSR) that is depleted as TAU is increasingly phosphorylated15 (Fig. 3c).