One such meta-analysis based on 40 case–control studies revealed that MTHFR C677T polymorphism might contribute to the risk of AD, particularly in APOE ε4 carriers (Peng et al., 2015), whereas another meta-analysis, which included only well-designed case–control studies and strict diagnostic criteria, held that MTHFR C677T variant might also influence susceptibility to AD in APOE ε4 non-carriers (odds ratio = 1.27; 95% confidence interval = 0.97–2.02) (Zhang et al., 2010). This evidence concerns the gene MTHFR and Alzheimer disease.