MAPT and primary progressive aphasia: The underlying neuropathology may differ between PPA subtypes: nfvPPA is often a primary tauopathy (frontotemporal lobar degenerations with tau inclusions (FTLD-tau)), svPPA is a TDP-43 proteinopathy (FTLD-TDP predominantly type C in the harmonized classification) [16], and lvPPA is a focal variant of Alzheimer's disease (AD) [17, 18].