MAPT and supranuclear palsy, progressive, 1: According to the fibrillated tau isoform (3R or 4R), primary tauopathies can be further classified into three major subtypes, including 3R tauopathies (such as PiD), 4R tauopathies (including PSP and corticobasal degeneration (CBD)), and mixed 3R/4R tauopathies [23].