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Gyrate Atrophy
Gyrate Atrophy of the choroid and retina is an autosomal recessive inherited retinal degeneration (IRD) which causes near-sightedness (myopia), cataracts and progressive vision loss.
What are the symptoms of Gyrate Atrophy?
Gyrate Atrophy was once thought to be a subtype of Choroideremia, but is now clearly distinguished by hyper-pigmentation of the remaining RPE. In addition to living with deteriorating visual acuity and near-sightedness, affected individuals can also experience night blindness within the first decade of life, as well as loss of peripheral vision.
What causes Gyrate Atrophy?
Gyrate Atrophy arises because of mutations in the OAT gene located on chromosome 10. When working normally, the OAT gene codes for the enzyme ornithine aminotransferase. This enzyme is active in the mitochondria and helps process excess nitrogen that is generated by protein breakdown. A deficiency in ornithine aminotransferase causes plasma ornithine levels to rise tenfold, which is toxic to the retinal pigment epithelium (RPE) and choroid1.
Gyrate Atrophy follows an autosomal recessive pattern of inheritance and only affects individuals who have two copies of the mutated OAT gene, one from each parent. People with only one mutated gene copy are known as “carriers” and are not affected by the condition but may pass the faulty gene copy to their children.
Genetic testing can help to identify mutations in the OAT gene and confirm a diagnosis of Gyrate Atrophy, while some newborn screening procedures also test for gyrate atrophy.
What treatments are available?
People living with Gyrate Atrophy are generally treated with a low arginine diet, although this can be quite restrictive and difficult to maintain. Vitamin B6 treatment lowers the plasma ornithine levels in a small percentage of gyrate atrophy patients.
Whether such a reduction improves the long-term visual outcome is unknown, but, unlike arginine restriction, vitamin supplementation is relatively easy to administer. Long-term vitamin therapy should be considered only for patients whose ornithine levels can be shown to drop in response to treatment.
References
1. American Academy of Ophthalmology. Available at https://www.aao.org/bcscsnippetdetail.aspx?id=4e9c5446-a64a-4cd2-874b-cafb19b8d2c3. Accessed April 2020.