MAPT and Alzheimer disease: AD-associated mutations in the MAPT gene either alter the amino acid sequence within tau protein—which induces hyperphosphorylation, leads to a reduced predisposition for microtubule assembly, and consequently leads to an increased tendency for aggregation—or imbalance tau’s isoforms due to unusual splicing, also triggering hyperphosphorylation and aggregation [20,114,115,116].