APOE and Alzheimer disease: In the second and third meta-analyses, we focused on the studies of Li L et al. [14] and Zhang MY et al. [15], who investigated the associations of cholesterol-24S-hydroxylase (CYP46A1) rs754203 and methylenetetrahydrofolate reductase (MTHFR) rs1801133 polymorphisms with AD according to apolipoprotein E ε4 (ApoE ε4) status.