MAPT and Alzheimer disease: Diverse tau proteinopathies (tauopathies) also occur sporadically (i.e., in the absence of MAPT or other pathogenic variants) and are subdivided into primary tauopathies—which collectively fall under the umbrella term, frontotemporal lobar degeneration (FTLD)-tau—and secondary tauopathies, the most prominent example of which is Alzheimer’s disease (AD).