PSEN2 and Alzheimer disease: Mutations in the APP gene and/or the enzymes involved in APP processing (γ-secretase components presenilins, PSEN1 and PSEN2; Chartier-Harlin et al., 1991; Goate et al., 1991; Murrell et al., 1991; Levy-Lahad et al., 1995; Rogaev et al., 1995; Sherrington et al., 1995) are correlated with early onset AD.