Genome-wide association studies have repeatedly shown that the ε4 allele of the apolipoprotein E (APOE) gene is the strongest known genetic risk factor for AD, increasing risk by 200–300% and decreasing age of onset, in a dose-dependent manner (Farrer et al., 1997; Bertram et al., 2007; Harold et al., 2009; Fei and Jianhua, 2013). The gene discussed is APOE; the disease is Alzheimer disease.