MTHFR and Cognitive impairment: Concerning the four SNPs of interest and the disease-related factors, cognitive impairment (SNPs of APOE, ADH1B, MTHFR), alcohol abuse (ADH1B variant), caffeine consumption (SNPs of CYP2A1, MTHFR), and homocysteine levels (MTHFR variant) appeared as the mostly represented traits.