MAPT and Alzheimer disease: These results strongly suggest that 3R and 4R tau isoforms are integrated in PHF at a ratio of 1:1 through the microtubule binding repeat regions of tau in AD, whereas only 3R tau isoforms in PiD and only 4R tau isoforms in CBD and PSP are integrated into fibrils through different microtubule binding regions [43,61,68].