MTHFR and Alzheimer disease: At best of our knowledge no previous study has investigated the relationship among biochemical markers of one-carbon metabolism (folate, hcy, vitamin B12) and genetic polymorphisms of major enzymes involved in this pathway (methylenetetrahydrofolate reductase: MTHFR; methionine synthase: MTR; methionine synthase reductase: MTRR; thymidylate synthase: TYMS; reduced folate carrier: RFC1; DNA methyltransferases: DNMTs) by means of ANNs in AD.