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Gyrate atrophy
This inherited eye condition leads to the gradual deterioration of the retina, the light-sensitive tissue at the back of the eye. It often results in night blindness and restricted visual fields, eventually progressing to significant vision impairment.
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Overview
Gyrate atrophy is a rare, inherited metabolic disorder that primarily impacts the eyes. It causes progressive degeneration of the choroid and retina, which are crucial structures for vision. The condition typically manifests with night blindness in childhood, followed by a gradual narrowing of the visual field [PMID:36523909]. Over time, this can lead to substantial vision loss, usually by early to mid-adulthood.
The underlying problem in gyrate atrophy is an excess of an amino acid called ornithine in the blood and other body fluids. This build-up is harmful to the cells in the eye, particularly those in the retina, leading to their progressive damage and loss [PMID:33678070].
Symptoms & clinical features
The initial symptom of gyrate atrophy is commonly night blindness (nyctalopia), often noticed in childhood or adolescence. Individuals may find it increasingly difficult to see in low-light conditions. As the condition progresses, peripheral vision becomes affected, leading to a gradual constriction of the visual field [PMID:33678070]. This means that the person's 'tunnel vision' may worsen over time.
Other symptoms can include blurred central vision in later stages, and in some individuals, the development of cataracts, which are cloudy areas in the lens of the eye. The severity and rate of progression can vary between individuals, even within the same family.
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Affected organs
Gyrate atrophy predominantly affects the eyes. Specifically, the retina and choroid are the primary structures impacted. The retina is the light-sensitive layer at the back of the eye that converts light into electrical signals sent to the brain. The choroid is a layer of blood vessels and connective tissue that provides oxygen and nutrients to the retina. The build-up of ornithine leads to atrophy, or wasting away, of these crucial eye tissues.
Risks & severity
Gyrate atrophy is a progressive condition, meaning its effects worsen over time. The severity of vision loss varies, but most individuals experience significant visual impairment, often leading to legal blindness, by early to mid-adulthood [PMID:36523909]. The age of onset for noticeable symptoms typically ranges from childhood to early adolescence. In some individuals, additional features like short stature, intellectual disability, or muscle weakness have been reported, although these are less common and less consistently observed than the eye involvement [PMID:33678070]. The exact prevalence of gyrate atrophy is not well established, but it is considered a very rare condition.
Genetic causes
Gyrate atrophy is caused by pathogenic variants in the OAT gene. This gene provides instructions for making an enzyme called ornithine aminotransferase. This enzyme plays a critical role in the normal metabolism (breakdown) of the amino acid ornithine [PMID:33678070].
When there are disease-causing changes in the OAT gene, the ornithine aminotransferase enzyme is either missing or does not function correctly. This leads to a build-up of ornithine in the body, which becomes toxic to the cells of the retina and choroid, ultimately causing their degeneration and the characteristic vision loss seen in gyrate atrophy.
- OAT ornithine aminotransferaseThe OAT gene provides instructions for the ornithine aminotransferase enzyme, which plays a vital role in the breakdown of ornithine and the balance of amino acids within the body.
Inheritance pattern
Gyrate atrophy is inherited in an autosomal recessive pattern. This means that an individual must inherit two copies of the altered OAT gene - one from each parent - to develop the condition. People who inherit only one copy of the altered gene are known as carriers. Carriers typically do not show symptoms of gyrate atrophy because their other, working copy of the gene can produce enough functional enzyme.
When two carriers have children, there is a 1 in 4 (25%) chance with each pregnancy that their child will inherit two altered copies of the OAT gene and develop gyrate atrophy. There is a 2 in 4 (50%) chance that their child will be a carrier, and a 1 in 4 (25%) chance that their child will inherit two normal copies of the gene and not be affected or a carrier.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
Diagnosis & testing
Diagnosis of gyrate atrophy is typically suspected based on characteristic eye findings identified during an ophthalmological examination, such as the distinctive scalloped pattern of atrophy in the retina. This is usually followed by blood tests to measure the levels of ornithine, which are typically significantly elevated [PMID:36523909].
Confirmation of the diagnosis involves genetic testing to identify pathogenic variants in the OAT gene. In the UK, genetic testing for inherited eye conditions, including gyrate atrophy, is part of the NHS Genomic Medicine Service (GMS) and may be accessed via the R205 Eye disorders - Retinal dystrophy R-code. Referrals for genetic testing and counselling are usually made through a clinical geneticist or an ophthalmologist.
Management & lifestyle
Currently, there is no cure for gyrate atrophy, but management aims to slow the progression of vision loss. Some individuals with specific types of OAT gene variants may respond to a diet restricted in arginine (an amino acid that the body uses to make ornithine) and supplemented with vitamin B6 (pyridoxine) [PMID:33678070]. This dietary management, supervised by a specialist dietitian, can help reduce ornithine levels.
Regular follow-up with an ophthalmologist is important to monitor the progression of the eye disease and manage any complications, such as cataracts. Genetic counselling is also recommended for affected individuals and their families to understand the inheritance pattern and reproductive risks. Research into new treatments, including gene therapy, is ongoing.
UK care pathway
In the UK, individuals with suspected inherited eye conditions like gyrate atrophy would typically be referred by their GP or ophthalmologist to an NHS clinical genetics service. These services provide comprehensive genetic counselling and access to diagnostic genetic testing through the NHS Genomic Medicine Service. Testing for gyrate atrophy falls under the R205 Eye disorders - Retinal dystrophy R-code, facilitating a standardised pathway for diagnosis and care. Genetic counsellors play a vital role in explaining the condition, its inheritance, and implications for family members.
Frequently asked questions
What is gyrate atrophy?
Gyrate atrophy is a rare genetic condition primarily affecting the eyes. It causes progressive damage to the retina and choroid, leading to night blindness and a gradual loss of peripheral vision, eventually impacting central vision.
How is gyrate atrophy inherited?
It is inherited in an autosomal recessive pattern. This means a person must inherit a faulty OAT gene from both parents to develop the condition. Parents who are carriers typically do not show symptoms themselves.
Can gyrate atrophy be treated?
There is no cure, but some individuals may benefit from a special diet low in arginine and supplemented with vitamin B6, which can help reduce ornithine levels and slow disease progression. Regular eye check-ups are also important.
Will my vision completely disappear?
Gyrate atrophy typically leads to significant vision impairment and often legal blindness by early to mid-adulthood. However, the exact rate and extent of vision loss can vary between individuals.
How is gyrate atrophy diagnosed?
Diagnosis usually involves an eye examination revealing characteristic retinal changes, blood tests showing high ornithine levels, and confirmation through genetic testing for variants in the OAT gene.
References
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