PSEN2 and Alzheimer disease: Mutations on the genes encoding for APP (Goate et al., 1991), Presenilin-1 (PS1) (Sherrington et al., 1995) and Presenilin-2 (PS2) (Levy-Lahad et al., 1995; Rogaev et al., 1995) are the cause of most familial cases of AD, with the onset of symptoms occurring between 30 and 60 years of age.