MAPT and Alzheimer disease: Tauopathies can be classified into the following three groups on the basis of the tau isoforms found in the aggregates from diseased brains: (1) 4R tauopathies, including progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and argyrophilic grain disease (AGD); (2) 3R tauopathies, including Pick disease (PiD); and (3) 3R + 4R tauopathies, including AD and chronic traumatic encephalopathy (CTE) [20, 21] (Fig. 1A–C).