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Normal Function
The OAT gene provides instructions for making an enzyme called ornithine aminotransferase (OAT). This enzyme is active in the energy-producing centers of cells (mitochondria), where it helps break down a molecule called ornithine. Ornithine is involved in the urea cycle, which gets rid of the excess nitrogen (in the form of ammonia) that is made when proteins are broken down to provide energy.
In addition to its role in the urea cycle, ornithine helps ensure the proper balance of protein building blocks (amino acids) in the body. This balance is important because a specific sequence of amino acids is required to build each of the many different proteins needed for the body's functions. OAT allows ornithine to be converted into another molecule called pyrroline-5-carboxylate (P5C). P5C can be converted into the amino acids proline and glutamate.
Glutamate serves as an important chemical messenger (neurotransmitter) that stimulates nerve cells (neurons) in the brain. Glutamate is essential for normal brain function and is used to make another important neurotransmitter called gamma-amino butyric acid (GABA). GABA helps slow down brain activity so the brain is not overloaded with signals.
Health Conditions Related to Genetic Changes
Gyrate atrophy of the choroid and retina
Genetic changes that cause disease are called pathogenic variants. Pathogenic variants in the OAT gene can cause gyrate atrophy of the choroid and retina (often simply called gyrate atrophy). Gyrate atrophy is an inherited disorder that is characterized by vision loss that worsens over time (progressive vision loss). The pathogenic variants that are associated with gyrate atrophy reduce the amount of functional OAT protein, which impairs the conversion of ornithine into P5C. As a result, extra ornithine can build up in the blood and other body fluids, including the clear liquid in the front of the eye (aqueous humor).
It is not clear exactly how these changes result in the progressive vision loss and other features that are associated with gyrate atrophy. Researchers have suggested that the buildup of ornithine may be toxic to cells in the specialized light-sensitive tissue that lines the back of the eye (retina
). It has also been proposed that excess ornithine may reduce the production of a molecule called creatine. Creatine is needed for many tissues in the body to properly store and use energy. It helps provide energy for muscle contraction and is also important for nervous system functioning, a feature that may explain the nerve disturbances and muscle weakness seen in some people with gyrate atrophy.
Other Names for This Gene
- OKT
- ornithine aminotransferase
- ornithine aminotransferase precursor
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- Aktasoglu EO, Ozdemir HB, Ozmen MC, Inci A, Okur I, Ezgu FS, Tumer L. Gyrate atrophy of the choroid and retina: a tertiary center experience. Orphanet J Rare Dis. 2026 Feb 16;21(1):104. doi: 10.1186/s13023-026-04265-x. Citation on PubMed
- Elnahry AG, Elnahry GA. Gyrate Atrophy of the Choroid and Retina: A Review. Eur J Ophthalmol. 2022 May;32(3):1314-1323. doi: 10.1177/11206721211067333. Epub 2021 Dec 13. Citation on PubMed
- Ginguay A, Cynober L, Curis E, Nicolis I. Ornithine Aminotransferase, an Important Glutamate-Metabolizing Enzyme at the Crossroads of Multiple Metabolic Pathways. Biology (Basel). 2017 Mar 7;6(1):18. doi: 10.3390/biology6010018. Citation on PubMed
- Mashima YG, Weleber RG, Kennaway NG, Inana G. Genotype-phenotype correlation of a pyridoxine-responsive form of gyrate atrophy. Ophthalmic Genet. 1999 Dec;20(4):219-24. doi: 10.1076/opge.20.4.219.2271. Citation on PubMed
- Mitchell GA, Brody LC, Looney J, Steel G, Suchanek M, Dowling C, Der Kaloustian V, Kaiser-Kupfer M, Valle D. An initiator codon mutation in ornithine-delta-aminotransferase causing gyrate atrophy of the choroid and retina. J Clin Invest. 1988 Feb;81(2):630-3. doi: 10.1172/JCI113365. Citation on PubMed or Free article on PubMed Central
- Montioli R, Bellezza I, Desbats MA, Borri Voltattorni C, Salviati L, Cellini B. Deficit of human ornithine aminotransferase in gyrate atrophy: Molecular, cellular, and clinical aspects. Biochim Biophys Acta Proteins Proteom. 2021 Jan;1869(1):140555. doi: 10.1016/j.bbapap.2020.140555. Epub 2020 Oct 14. Citation on PubMed
- Ohkubo Y, Ueta A, Ito T, Sumi S, Yamada M, Ozawa K, Togari H. Vitamin B6-responsive ornithine aminotransferase deficiency with a novel mutation G237D. Tohoku J Exp Med. 2005 Apr;205(4):335-42. doi: 10.1620/tjem.205.335. Citation on PubMed
- Peltola KE, Nanto-Salonen K, Heinonen OJ, Jaaskelainen S, Heinanen K, Simell O, Nikoskelainen E. Ophthalmologic heterogeneity in subjects with gyrate atrophy of choroid and retina harboring the L402P mutation of ornithine aminotransferase. Ophthalmology. 2001 Apr;108(4):721-9. doi: 10.1016/s0161-6420(00)00587-x. Citation on PubMed
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