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MOCS2 gene

molybdenum cofactor synthesis 2

Normal Function

The MOCS2 gene provides instructions for making two different proteins, MOCS2A and MOCS2B, which combine to form an enzyme called molybdopterin synthase. Molybdopterin synthase performs the second of a series of reactions in the formation (biosynthesis) of a molecule called molybdenum cofactor. Molybdenum cofactor, which contains the element molybdenum, is essential to the function of several enzymes called sulfite oxidase, aldehyde oxidase, xanthine dehydrogenase, and mitochondrial amidoxime reducing component (mARC). These enzymes help break down (metabolize) different substances in the body, some of which are toxic if not metabolized.

Health Conditions Related to Genetic Changes

Molybdenum cofactor deficiency

MOCS2 gene mutations cause a disorder called molybdenum cofactor deficiency. This disorder is characterized by seizures that begin early in life and brain dysfunction that worsens over time (encephalopathy); the condition is usually fatal by early childhood. At least a dozen mutations in the MOCS2 gene have been found to cause a form of the disorder designated type B or complementation group B.

The MOCS2 gene mutations involved in molybdenum cofactor deficiency likely eliminate the function of MOCS2A, MOCS2B, or both, although in rare cases that are less severe, some protein function may remain. Without either piece of molybdopterin synthase, molybdenum cofactor biosynthesis is impaired. Loss of the cofactor impedes the function of the metabolic enzymes that rely on it.

The resulting loss of enzyme activity leads to buildup of certain chemicals, including sulfite, S-sulfocysteine, xanthine, and hypoxanthine, and low levels of another chemical called uric acid. (Testing for these chemicals can help in the diagnosis of this condition.) Sulfite, which is normally broken down by sulfite oxidase, is toxic, especially to the brain. Researchers suggest that damage caused by the abnormally high levels of sulfite (and possibly other chemicals) leads to encephalopathy, seizures, and the other features of molybdenum cofactor deficiency.

More About This Health Condition

Other Names for This Gene

  • MOCO1
  • molybdenum cofactor biosynthesis protein E
  • molybdopterin synthase catalytic subunit large subunit MOCS2B
  • molybdopterin synthase small and large subunit
  • molybdopterin synthase sulfur carrier subunit
  • molybdopterin synthase sulfur carrier subunit small subunit MOCS2A
  • MPTS

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Leimkuhler S, Charcosset M, Latour P, Dorche C, Kleppe S, Scaglia F, Szymczak I, Schupp P, Hahnewald R, Reiss J. Ten novel mutations in the molybdenum cofactor genes MOCS1 and MOCS2 and in vitro characterization of a MOCS2 mutation that abolishes the binding ability of molybdopterin synthase. Hum Genet. 2005 Oct;117(6):565-70. doi: 10.1007/s00439-005-1341-9. Epub 2005 Jul 14. Citation on PubMed
  • Leimkuhler S, Freuer A, Araujo JA, Rajagopalan KV, Mendel RR. Mechanistic studies of human molybdopterin synthase reaction and characterization of mutants identified in group B patients of molybdenum cofactor deficiency. J Biol Chem. 2003 Jul 11;278(28):26127-34. doi: 10.1074/jbc.M303092200. Epub 2003 May 5. Citation on PubMed
  • Mendel RR. The molybdenum cofactor. J Biol Chem. 2013 May 10;288(19):13165-72. doi: 10.1074/jbc.R113.455311. Epub 2013 Mar 28. Citation on PubMed or Free article on PubMed Central
  • Reiss J, Johnson JL. Mutations in the molybdenum cofactor biosynthetic genes MOCS1, MOCS2, and GEPH. Hum Mutat. 2003 Jun;21(6):569-76. doi: 10.1002/humu.10223. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.