PSEN1 and Alzheimer disease: Genetic factors underlie AD pathophysiology, with gene variants of APP, PSEN1 and PSEN2 leading to early AD onset (EOAD) in familial forms of the disease, and the APOE ε4 allele being associated with increased disease severity in EOAD as well as in late-onset forms (LOAD) of familial and sporadic AD [4,5].