Patients with familial Alzheimer's disease (FAD) carry mutations in either the APP (Goate et al., 1991), presenilin 1 (PSEN1) (Sherrington et al., 1995) or presenilin 2 genes (PSEN2) (Rogaev et al., 1995; Finckh et al., 2000) (Fig. 2). This evidence concerns the gene PSEN2 and familial Alzheimer disease.