MAPT and Alzheimer disease: Furthermore, morphological differences exist among different diseases or disease types as different tau isoforms are accumulated in diseased brains, namely, six tau isoforms in AD, 3R tau isoforms in Pick’s disease, and 4R tau isoforms in profressive supranuclear palsy (PSP) and cortical basal degeneration (CBD; Goedert and Spillantini, 2011).