In addition to ADMA, uremic environment, hyperhomocysteinemia (Hcy) and oxidative stress may affect DNA methylation. S-adenosylmethionine (SAM) is an important human methyl donor. S-adenosylhomocysteine (SAH) is demethylated product. Methylenetetrahydrofolate reductase (MTHFR), a folate metabolism enzyme can regulate methylation pathway.