PSEN1 and familial Alzheimer disease: Most mutations in the presenilin 1 (PSEN 1) gene, which codes for the catalytic component of γ-secretase [8], result in the overproduction of Aβ, specifically, the 42-amino acid Aβ isoform (Aβ1–42, hereafter Aβ42) [9], and occur most frequently in familial AD (FAD; http://www.molgen.ua.ac.be/ADMutations/).