The APOE ε4 homozygote is a validated risk factor with significant effects, and its HRs of all-cause dementia and AD were 6.93 (95% CI, 6.05–7.92; P < 0.001) and 12.91 (95% CI, 10.59–15.75; P < 0.001) in this study. The gene discussed is APOE; the disease is dementia.