Interestingly, the 'one-carbon pool by folate' pathway, which contains the MTHFR and MTHFD1L genes, was nominally significant for bipolar disorder, showed a trend for major depressive disorder and was not significant for schizophrenia, suggesting that this pathway has distinct effect on mood disorders, probably through a common intermediate phenotype, such as ruminative response style. Here, MTHFR is linked to bipolar disorder.