MAPT and Alzheimer disease: Quantification of tau phosphorylated at Ser396/404, as detected by the PHF-1 antibody, showed that tau phosphorylation at this epitope is below the detectable range in control brain, and in most Braak stage II-V tissues, but was significantly increased at end-stage AD (Braak VI) when compared to control (p < 0.001; Fig. 1a).