PSEN2 and familial Alzheimer disease: Though ApoE4 is a well-characterized risk factor in SAD, disease etiology in FAD is attributed to mutations of amyloid precursor protein (APP), presenilin1 (PS1), and presenilin 2 (PS2) genes (Goate et al., 1991; Levy-Lahad et al., 1995; Rogaev et al., 1995; Sherrington et al., 1996; Selkoe, 2001b).