PSEN2 and Alzheimer disease: Familial AD exhibits typical Mendelian inheritance of mutations or CNVs in APP or mutations in the secretase genes, PSEN1 (Sherrington et al., 1995) and PSEN2 (Levy-Lahad et al., 1995; Rogaev et al., 1995) that alter Aβ processing and lead to early-onset AD.