PSEN2 and Alzheimer disease: Interactionsamong environmental agents, advancing age (Tanzi andBertram, 2001; Grant et al.,2002) and a certain genetic polymorphisms (Bertram and Tanzi, 2005) account for 95% of sporadic late-onset AD, whileonly 5% AD are of early-onset type and due to mutations in APP (Goate et al., 1991), presenilin-1(PSEN-1) (Sherrington etal., 1995) and presenilin-2 (PSEN-2) (Levy-Lahad et al., 1995; Rogaev et al., 1995) genes onchromosome 21, 14 and 1, respectively.