GRN and Alzheimer disease: Although the vast majority of PPA cases are sporadic, few familial cases of PPA with pathological variants in the genes associated with FTLD have been reported: microtubule-associated protein tau (MAPT), granulin precursor (GRN), and C9orf72, as well as in the presenilin 1 (PSEN1) gene, which causes early onset AD.