MAPT and primary progressive aphasia: PPA became one of the first syndromes to show that the same clinical phenotype can be caused by heterogeneous pathologies.22,23 Three major neuropathologic entities account for the majority of PPA cases: AD, frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), and frontotemporal lobar degeneration with tau inclusions (FTLD-tau).21 Like PPA, bvFTD is also a clinically heterogeneous syndrome, but the majority of cases show either FTLD-tau or FTLDTDP.