MAPT and Alzheimer disease: Primary tauopathies containing tau aggregates formed by 4R tau isoforms include corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), 3R tau isoforms are primarily found in Pick’s disease (PiD), whereas Alzheimer’s disease (AD) and primary age-related tauopathy (PART) are mixed 3R + 4R tauopathies [6] (Fig. 1).