MAPT and argyrophilic grain disease: Tauopathies are often classified based on the primary tau protein isoform deposited in the brain, including 3R tauopathies, exemplified by Pick’s disease (PiD); 4R tauopathies, such as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), argyrophilic grain disease (AGD), and globular glial tauopathy (GGT); and combined 3R/4R tauopathies, such as Alzheimer’s disease (AD), chronic traumatic encephalopathy (CTE), and primary age-related tauopathy (PART).