PSEN2 and Down syndrome: George-Hyslop et al., 1992; Li et al., 1995; Sherrington et al., 1995) and presenilin 2 (PSEN2) gene (Levy-Lahad et al., 1995a,b; Rogaev et al., 1995), a duplication of APP locus, as well as trisomy of chromosome 21 causing Down syndrome (DS; Campion et al., 1999; Bettens et al., 2013).