MAPT and Alzheimer disease: This commonly used Braak staging system describes that early on in AD (stage I), tau accumulation begins in the transentorhinal cortex and subsequentially involves the rest of the entorhinal cortex and portions of the anterior hippocampus (stage II) (Braak & Braak, 1991; Braak et al., 2006; Braak et al., 2011).