Individuals with the APOE-ε4 allele are predisposed to accumulate Aβ (Castellano et al., 2011) and are at significantly higher AD risk (Poirier et al., 1993; Strittmatter et al., 1993), whereas the ε2 allele is protective against AD (Corder et al., 1994). The gene discussed is APOE; the disease is Alzheimer disease.