Given that a deficiency of the Mme gene encoding NEP in the mouse brain resulted in a twofold increase in Aβ40 and Aβ42 (Iwata et al., 2001), and considering the number of studies consistently demonstrating an aging-dependent or AD-associated decline of NEP expression in the human and mouse brain (Iwata et al., 2002; Wang et al., 2003; Russo et al., 2005; Hellstrom-Lindahl et al., 2008), the aging-associated decrease in brain NEP expression likely plays a role in the pathogenesis of SAD (Iwata et al., 2001, 2005). Here, MME is linked to Alzheimer disease.