However, it is worthy of mentioning that although there was association between the 222Val/Val genotype and depression, anxiety, and cognitive impairment, which are conditions associated with suicidal behavior49, our results indicated association of attempted suicide with the Ala/Val genotype but not with Val/Val genotype, suggesting a heterozygous effect of the MTHFR Ala222Val gene polymorphism on suicidal behavior. Here, MTHFR is linked to major depressive disorder.