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OTC gene

ornithine transcarbamylase

Normal Function

The OTC gene provides instructions for making the enzyme ornithine transcarbamylase. This enzyme participates in the urea cycle, a series of reactions that occurs in liver cells. The urea cycle processes excess nitrogen, generated when protein is used by the body, into a compound called urea that is excreted by the kidneys. Excreting the excess nitrogen prevents it from accumulating in the form of ammonia, which is toxic, especially to the nervous system.

The specific role of the ornithine transcarbamylase enzyme is to control the reaction in which two compounds, carbamoyl phosphate and ornithine, form a new compound called citrulline.

Health Conditions Related to Genetic Changes

Ornithine transcarbamylase deficiency

More than 500 OTC gene mutations have been identified in people with ornithine transcarbamylase deficiency, an inherited disorder that causes ammonia to accumulate in the blood. Ammonia, which is formed when proteins are broken down in the body, is toxic if the levels become too high. The nervous system is especially sensitive to the effects of excess ammonia.

The OTC gene mutations that cause ornithine transcarbamylase deficiency result in an ornithine transcarbamylase enzyme that is shorter than normal or the wrong shape, or prevent any enzyme from being produced. The shape of an enzyme affects its ability to control a chemical reaction. If the ornithine transcarbamylase enzyme is misshapen or missing, it cannot fulfill its role in the urea cycle. Excess nitrogen is not converted to urea for excretion, and ammonia accumulates in the body. Accumulation of ammonia causes neurological problems and other signs and symptoms of ornithine transcarbamylase deficiency.

More About This Health Condition

Other Names for This Gene

  • MGC129967
  • MGC129968
  • OCTD
  • ornithine carbamoyltransferase precursor
  • ornithine transcarbamylase

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


  • Ah Mew N, Simpson KL, Gropman AL, Lanpher BC, Chapman KA, Summar ML. Urea Cycle Disorders Overview. 2003 Apr 29 [updated 2017 Jun 22]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from Citation on PubMed
  • Brassier A, Gobin S, Arnoux JB, Valayannopoulos V, Habarou F, Kossorotoff M, Servais A, Barbier V, Dubois S, Touati G, Barouki R, Lesage F, Dupic L, Bonnefont JP, Ottolenghi C, De Lonlay P. Long-term outcomes in Ornithine Transcarbamylase deficiency: a series of 90 patients. Orphanet J Rare Dis. 2015 May 10;10:58. doi: 10.1186/s13023-015-0266-1. Citation on PubMed or Free article on PubMed Central
  • Caldovic L, Abdikarim I, Narain S, Tuchman M, Morizono H. Genotype-Phenotype Correlations in Ornithine Transcarbamylase Deficiency: A Mutation Update. J Genet Genomics. 2015 May 20;42(5):181-94. doi: 10.1016/j.jgg.2015.04.003. Epub 2015 May 19. Citation on PubMed or Free article on PubMed Central
  • Choi JH, Lee BH, Kim JH, Kim GH, Kim YM, Cho J, Cheon CK, Ko JM, Lee JH, Yoo HW. Clinical outcomes and the mutation spectrum of the OTC gene in patients with ornithine transcarbamylase deficiency. J Hum Genet. 2015 Sep;60(9):501-7. doi: 10.1038/jhg.2015.54. Citation on PubMed
  • Helman G, Pacheco-Colon I, Gropman AL. The urea cycle disorders. Semin Neurol. 2014 Jul;34(3):341-9. doi: 10.1055/s-0034-1386771. Epub 2014 Sep 5. 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.