MAPT and Alzheimer disease: Other investigational products, such as MK-6240 and PI-2620, can visualize tau lesions of Alzheimer’s disease and other diseases where 3-repeat and 4-repeat tau are mixing; however, they are scarcely able to detect tau lesions of tauopathies where only 4-repeat tau accumulates, such as progressive supra-nuclear palsy and cortico-basal degeneration [17, 18].