Progressive Retinal Atrophy in Cats
Progressive retinal atrophy (PRA) is a degenerative disorder of the retina. In case you’re a little rusty with your eye anatomy, the retina is the light-gathering tissue inside the eye that acts like the film in a camera. PRA leads to degeneration of the retinalphotoreceptors (the cells in the retina reactive to light). In cats, PRA can be either inherited or acquired.
Inherited progressive retinal atrophy
In cats, 2 different genes have been identified as causes of PRA:
- CEP290 is a gene that encodes for a protein known as centrosomal protein 290 kDa. This protein maintains the important structure known as the cilium in rod photoreceptors. Progressive retinal atrophy caused by CEP290 is autosomal recessive, meaning that in order for an animal to be affected, that animal needs to have inherited two mutated genes. Animals that have one mutated gene are unaffected, but are carriers and can transmit the disease. Progressive retinal atrophy, secondary to CEP290, is more common in certain breeds, such as the Abyssinian, Somali, and Ocicat. In addition, mutations of CEP290 have been found in other breeds, such as the American Curl, American Wirehair, Bengal, Balinese/Javanese, Colorpoint Shorthair, Cornish Rex, Munchkin, Oriental Shorthair, Peterbald, Siamese, Singapura, and Tonkinese.
- CRX (also found in Abyssinian and Somali cats) encodes for a transcription factor critical for the development of the retina. Unlike CEP290, mutations in CRX gene cause autosomal dominant progressive retinal atrophy in cats. In order for an animal to be affected, it only has to inherit one mutated gene. As a result, autosomal dominant PRA is usually present across many generations since offspring of an affected parent have a 50% chance of inheriting the mutated gene.
Toxicity causing progressive retinal atrophy
Exposure to certain antibiotics has been associated with progressive retinal atrophy in cats:
Fluoroquinolone enrofloxacin was first reported to cause PRA in cats, especially when used in higher doses and for longer periods of time. Fortunately, the incidence of enrofloxacin-associated PRA has decreased since the recommended dose was lowered to 5 mg/kg/day. Testing of the related antibiotic orbifloxacin has also been reported to cause PRA at higher doses. If fluoroquinolone-associated PRA is suspected, the antibiotic should be discontinued immediately to avoid additional damage to the retina. Before starting treatment with these antibiotics, talk with your veterinarian about the risk of PRA.
Nutritional deficiency causing progressive retinal