Because the Aβ42/Aβ40 ratio is increased, and over 150 missense mutations in PSEN1/2 have been linked to AD pathogenesis, a large amount of research has investigated the function of the γ-secretase complex in the context of AD (De Strooper et al., 2012; Haass et al., 2012; Mucke, 2012). This evidence concerns the gene PSEN1 and Alzheimer disease.