MAPT and semantic dementia: FTDP-17 is a heterogeneous clinicopathological entity, with the long arm of chromosome 17 harboring both the progranulin gene and MAPT. Heterozygous loss-of-function mutations in the progranulin gene give rise to FTDP-17 with abundant TAR DNA-binding protein 43 (TDP-43) inclusions37–40, whereas heterozygous gain-of-toxic function mutations in MAPT give rise to FTDP-17 with abundant tau inclusions6,7,41.