MAPT and supranuclear palsy, progressive, 1: Tau is known to have a higher affinity for GDP microtubules compared with GTP microtubules (32, 46, 47), and we recently discovered the N-terminal disease–associated mutation in Tau, R5L, associated with PSP, does not reduce affinity for either Taxol-microtubules or GMPCPP-microtubules (32).