The GNMT gene provides instructions for producing the enzyme glycine N-methyltransferase. This enzyme is involved in a multistep process that breaks down the protein building block (amino acid) methionine. Specifically, glycine N-methyltransferase starts a reaction that converts the compounds glycine and S-adenosylmethionine (also called AdoMet) to N-methylglycine and S-adenosylhomocysteine (also called AdoHcy).
This reaction also helps to control the relative amounts of AdoMet and AdoHcy. The AdoMet to AdoHcy ratio is important in many body processes, including the regulation of other genes by the addition of methyl groups, consisting of one carbon atom and three hydrogen atoms (methylation). Methylation is important in many cellular functions. These include determining whether the instructions in a particular segment of DNA are carried out, regulating reactions involving proteins and lipids, and controlling the processing of chemicals that relay signals in the nervous system (neurotransmitters).
The glycine N-methyltransferase enzyme is also involved in processing toxic compounds in the liver.
Three mutations in the GNMT gene have been described in individuals with hypermethioninemia. In an Italian family, one mutation substitutes the amino acid proline for the amino acid leucine at protein position 49 (written as Leu49Pro or L49P) and another mutation substitutes the amino acid asparagine for the amino acid histidine at position 176 (written as His176Asn or H176N). In a Greek patient of Roma origin, a mutation was identified that substitutes the amino acid serine for the amino acid asparagine at position 140 (written as Asn140Ser or N140S). The reduced glycine N-methyltransferase activity resulting from these mutations causes hypermethioninemia in affected individuals.
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Certain inherited variations in the GNMT gene have been associated with an increased risk of liver and prostate cancers. Other GNMT gene mutations that have been found in cancerous tumors are acquired during a person's lifetime and are present only in certain cells. These changes, which are called somatic mutations, are not inherited. GNMT gene mutations likely impair glycine N-methyltransferase functions such as processing potential cancer-causing substances in the liver and helping to regulate other genes, including those responsible for controlling cell growth. When cells grow too rapidly or in an uncontrolled way, a cancerous tumor can form.
- Glycine Methyltransferase
- Glycine Sarcosine Methyltransferase
- Glycine Sarcosine N-Methyltransferase