It is caused by mutations in the ornithine aminotransferase (OAT) gene, located on chromosome 10, which results in a 10- to 15-fold increase in plasma concentration of ornithine. The chorioretinal degenerative changes are caused by the hyperornithinemia, but the exact pathogenesis is unknown.
Patients with GA have hyperpigmented fundi, with lobular loss of the retinal pigment epithelium (RPE) and choroid. In early stages, patients have numerous, well-demarcated areas of atrophy of the RPE and choroid in the peripheral retina. These gradually coalesce and advance posteriorly to form a classic scalloped border at the junction of the normal and abnormal RPE. The ongoing atrophy of the choroid and retina causes progressively worsening nyctalopia (night blindness), visual field loss, myopia, posterior subcapsular cataracts, and a decline in visual acuity later in the course of the disease. Complete loss of vision, associated with macular involvement, typically occurs by the fourth or fifth decade of life.
The treatment goal in GA is to maintain normal serum ornithine levels. This has proven difficult, due to the rarity of the disease and allelic heterogeneity of the disease.
H31.23 – Gyrate atrophy, choroid
314467007 – Gyrate Atrophy
Differential Diagnosis & Pitfalls
- Choroideremia – Generalized hyperpigmentation of the remaining RPE helps to distinguish GA from choroideremia. Also, choroideremia is X-linked recessive.
- (RP) – RP would have bony spicules in retina, retinal arteriolar narrowing, and optic nerve waxy pallor.
- Sorsby macular dystrophy
- Pathologic myopia – The scalloped borders surround the optic nerve as opposed to being peripheral as in GA.
- Aicardi syndrome – X-linked dominant. Also, the retinal lacunae are larger and more solitary.