MAPT and Alzheimer disease: In patients with sporadic AD, tau pathology in cortex begins in layer II of the transentorhinal and entorhinal cortices (ERC; Tau stages I-II), and then spreads to closely interconnected circuits in the limbic/association cortices and hippocampus (Tau stages III-IV) (Braak et al., 2011; Hyman et al., 1984).