APOE and Cognitive impairment: According to a population-based cohort study, lifetime risk of mild cognitive impairment (MCI) or dementia is 30–35% for APOE4 homozygote individuals, 20–25% for APOE4 heterozygote individuals (ε3/ε4 and ε2/ε4), and 10–15% for non APOE4 individuals (ε3/ε3, ε3/ε2, and ε2/ε2) (Qian et al., 2017).