APP and Alzheimer disease: Progranulin (GRN) and microtubule-associated protein tau (MAPT) mutations are associated with familial frontotemporal dementia, but recently some have also been found in clinically diagnosed AD cases [10,11], and a recent study suggested that mutations in MAPT and GRN can be found in clinical AD with a frequency comparable to that of mutations in APP, PSEN1, and PSEN2 [7].