MAPT and frontotemporal dementia: The neuropathological substrate of bvFTD, nfvPPA, and svPPA is frontotemporal lobar degeneration (FTLD), which is characterized by progressive atrophy of the frontal and temporal lobes of the brain and is in turn classified into three distinct pathological entities: FTLD-tau (comprising approximately 45% of cases), FTLD-TDP (50%), and the rare FTLD-FUS (5%), characterized by intracellular inclusions of pathologically modified forms of the proteins tau, TDP-43 and FUS, respectively (Mann and Snowden, 2017).