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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed June 2006

What is the official name of the OTC gene?

The official name of this gene is “ornithine carbamoyltransferase.”

OTC is the gene's official symbol. The OTC gene is also known by other names, listed below.

What is the normal function of the OTC gene?

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.

How are changes in the OTC gene related to health conditions?

ornithine transcarbamylase deficiency - caused by mutations in the OTC gene

More than 200 OTC gene mutations have been identified in people with ornithine transcarbamylase deficiency. A mutated OTC gene may result in an ornithine transcarbamylase enzyme that is shorter than normal or the wrong shape, or may prevent the enzyme from being produced at all.

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. Ammonia is toxic, especially to the nervous system, so this accumulation causes neurological problems and other signs and symptoms of ornithine transcarbamylase deficiency.

Where is the OTC gene located?

Cytogenetic Location: Xp21.1

Molecular Location on the X chromosome: base pairs 38,352,483 to 38,421,450

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The OTC gene is located on the short (p) arm of the X chromosome at position 21.1.

The OTC gene is located on the short (p) arm of the X chromosome at position 21.1.

More precisely, the OTC gene is located from base pair 38,352,483 to base pair 38,421,450 on the X chromosome.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about OTC?

You and your healthcare professional may find the following resources about OTC helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the OTC gene or gene products?

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

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding OTC?

ammonia ; compound ; deficiency ; enzyme ; excretion ; gene ; nervous system ; neurological ; phosphate ; precursor ; protein ; toxic ; urea

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Azevedo L, Calafell F, Vilarinho L, Amorim A. Haplotype analysis and phylogeny of ornithine transcarbamylase polymorphisms. Ann Hum Genet. 2002 Nov;66(Pt 5-6):379-85. (
  • Azevedo L, Climent C, Vilarinho L, Calafell F, Amorim A. Evidence for mutational cis-acting factors affecting mutagenesis in the ornithine transcarbamylase gene. Hum Mutat. 2004 Sep;24(3):273. (
  • Azevedo L, Stolnaja L, Tietzeova E, Hrebicek M, Hruba E, Vilarinho L, Amorim A, Dvorakova L. New polymorphic sites within ornithine transcarbamylase gene: population genetics studies and implications for diagnosis. Mol Genet Metab. 2003 Feb;78(2):152-7. (
  • Bisanzi S, Morrone A, Donati MA, Pasquini E, Spada M, Strisciuglio P, Parenti G, Parini R, Papadia F, Zammarchi E. Genetic analysis in nine unrelated Italian patients affected by OTC deficiency: detection of novel mutations in the OTC gene. Mol Genet Metab. 2002 Jun;76(2):137-44. (
  • Climent C, Rubio V. H intragenic polymorphisms and haplotype analysis in the ornithine transcarbamylase (OTC) gene and their relevance for tracking the inheritance of OTC deficiency. Hum Mutat. 2002 Nov;20(5):407-8. (
  • Climent C, Rubio V. Identification of seven novel missense mutations, two splice-site mutations, two microdeletions and a polymorphic amino acid substitution in the gene for ornithine transcarbamylase (OTC) in patients with OTC deficiency. Hum Mutat. 2002 Feb;19(2):185-6. (
  • Gene Review: Urea Cycle Disorders Overview (
  • Mavinakere M, Morizono H, Shi D, Allewell NM, Tuchman M. The clinically variable R40H mutant ornithine carbamoyltransferase shows cytosolic degradation of the precursor protein in CHO cells. J Inherit Metab Dis. 2001 Nov;24(6):614-22. (
  • NCBI Gene (
  • Tuchman M, Jaleel N, Morizono H, Sheehy L, Lynch MG. Mutations and polymorphisms in the human ornithine transcarbamylase gene. Hum Mutat. 2002 Feb;19(2):93-107. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: June 2006
Published: February 8, 2016