MAPT and semantic dementia: The identification of tau protein aggregates as the core unit of NFTs, but also the discovery of mutations in the MAPT gene that represent defined causes for a hereditary form of frontotemporal dementia (FTDP-17) [94,95,96], implied an important and—at least in some cases—direct role for tau in the pathogenesis of neurodegenerative diseases, even in the absence of Aβ pathology.