Glycine N-Methyltransferase (GNMT) is a tetrameric cytosolic protein. GNMT catalyzes the synthesis of N-methylglycine from glycine using S-adenosylmethionine (AdoMet) as the methyl donor. It can affects DNA methylation by regulating the ratio of S-adenosylmethionine to S-adenosylhomocystine, playing an important role in maintaining normal AdoMet levels. GNMT is highly expressed in liver. As a major folate-binding protein, GNMT takes part in the detoxification pathway. Defects in GNMT are the cause of hypermethioninemia. the patients with this deficiency are mild hepatomegaly and chronic elevation of serum transaminases.