PSEN2 and Alzheimer disease: Finally, we included the three genes that can cause early-onset AD when mutated: PSEN1 (Campion et al., 1995), PSEN2 (Rogaev et al., 1995), and APP (Levy et al., 1990; Van Broeckhoven et al., 1990), yielding a list of 40 genes associated with AD risk (Supplementary file 1).