Strong evidence from clinical and basic research indicates that among the three major ApoE allelic variants, the ApoEε4 allele is associated with an increased risk of AD (Corder et al., 1993; Saunders et al., 1993) while the ApoEε2 allele is linked to a decreased risk (Farrer et al., 1997; Corder et al., 1994) compared to the more common ApoEε3 allele (Bu, 2009; Liu et al., 2013). Here, APOE is linked to Alzheimer disease.