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OAT gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

OAT gene

The OAT gene provides instructions for making an enzyme essential for breaking down ornithine and maintaining the balance of amino acids in the body.

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 that cause gyrate atrophy of the choroid and retina (often simply called gyrate atrophy) reduce the amount of functional OAT protein. 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 cause cells to make a version of the OAT protein that does not properly convert 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. 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

Frequently Asked Questions

Because the OAT enzyme is deficient or absent in gyrate atrophy, the body cannot properly break down ornithine. Consuming high amounts of protein increases the production of ornithine, leading to toxic accumulation levels that accelerate the degeneration of the choroid and retina. Therefore, strict lifelong restriction of protein intake is the primary management strategy to slow vision loss, often requiring specialized medical nutrition therapy to balance essential amino acids while keeping ornithine levels low.
Early signs often include night blindness (nyctalopia) and difficulty seeing in low light, which may appear in childhood or adolescence. As the disease progresses, the peripheral (side) vision is lost first, creating a tunnel vision effect. Without strict dietary management, the condition can lead to severe central vision loss and legal blindness by early adulthood, though the rate of progression varies significantly based on how well ornithine levels are controlled.
Gyrate atrophy is an autosomal recessive disorder caused by pathogenic variants in the OAT gene. This means an individual must inherit two defective copies of the gene, one from each parent, to develop the condition. Parents who are carriers typically have no symptoms but have a 25 percent chance with each pregnancy of having a child with gyrate atrophy. Genetic counseling is recommended for family members to assess carrier status and reproductive risks.
Yes, ophthalmologists can detect early changes in the retina and choroid using fundus photography and optical coherence tomography (OCT) even before patients report significant vision problems. Blood tests measuring plasma ornithine levels are also critical for diagnosis and monitoring. Regular monitoring of these biomarkers allows clinicians to adjust dietary restrictions promptly to prevent irreversible damage to the eye tissues.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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