MTHFR and neoplasm: It has been shown that miR-22 could inhibit the formation of S-adenosylmethionine (SAM) by directly targeting key enzymes in the folate metabolism, methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) and methylenetetrahydrofolate reductase (MTHFR), thereby inducing hypomethylation of tumor suppressor genes and suppressing cancer cell proliferation [29].