While AD and FTDP-17 are mixed 3R and 4R tauopathies, reflecting the physiological ratio of expressed tau isoforms in the healthy brain [88], CBD/PSP, and AGD are classified as 4R tauopathies, as the pathological inclusions are predominantly constituted by 4R-tau [84]. The gene discussed is MAPT; the disease is argyrophilic grain disease.