Supporting the validity of [18F]PI-2620 to bind to 4R tau, we have shown consistently that [18F]PI-2620 binds to 4R tau in vitro [20], that [18F]PI-2620 autoradiography colocalizes with AT8 tau stainings in post-mortem PSP tissue [15, 20], and that the ante-mortem [18F]PI-2620 signal in the pallidum is associated with post-mortem assessed AT8 tau staining intensity and [18F]PI-2620 autoradiography [25]. The gene discussed is MAPT; the disease is supranuclear palsy, progressive, 1.