MTHFR and breast cancer: To investigate whether SNORD3A enhanced the chemosensitivity of breast cancer cells to 5-FU via modulating a metabolic pathway for 5-FU, we examined the expression of 5-FU metabolic-related genes, including uridine monophosphate synthetase (UMPS), thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and methylene tetrahydrofolate reductase (MTHFR).