Feline Progressive Retinal Atrophy (PRA-rdAc)
Feline progressive retinal atrophy is a hereditary eye disorder in cats, which belongs to a wider group of disorders, the progressive retinal atrophies. Progressive retinal atrophy (PRA) includes autosomal recessively inherited diseases that lead to degeneration of retinal photoreceptor cells in cats,dogs and other pets. Feline Progressive Retinal Atrophy (PRA-rdAc) is an equivalent to retinitis pigmentosa (RP), an inherited eye disorder affecting human beings. In cats, there are two main forms of PRA, ”rdAc” and ”Rdy”. PRA-rdAc is characterized by progressive degeneration of the photoreceptors in the retina, while ”Rdy” is a different form of blindness called ”rode cone dysplasia”.
There are two types of photoreceptors in the eye, rods and cones. Rods have an important role for vision in dim light and also night vision. The photoreceptors are localized in the retina, an important part of eye which takes the light and coverts it into electrical nerve signals which are sent to brain. PRA affects the retina in way that it causes rode degeneration. This way PRA leads to night blindness.
In PRA affected, photoreceptors develop after kitten’s birth, but as the cat ages, the receptor degenerate. Loss of retinal function is recorded by 8 months of age with early funduscopic changes detectable at 1 to 2 years of age. First symptom is night blindness, which with time progresses to complete blindness. Complete visual impairment onsets by 5 to 6 months of age. Eye of an affected cat may seem red, squinty and with excessive tearing. Night blindness can be observed through behavioral changes, such as cat’s refusal to go downstairs or down a dark hallway. With the disease’s progression, pupils will appear as dilated and reflection of light from the back of the eye may be noticed. Sometimes, the lens of the eye of an affected animal will become cloudy.
In an affected cat, PRA can be diagnosed through ophthalmic examination of characteristic changes in the retina. Another way of diagnostics is via electroretinography. Due to later onset and progressive nature of the disorder, PRA in cat may be unobserved for years.
Feline Progressive Retinal Atrophy (PRA-rdAc) is an inherited autosomal recessive disease. It is caused by a mutation in CEP290 gene. The allele shows widespread distribution, and has been documented in 37% cat breeds, with high frequency in North American and European Siamese populations.
Cat can be clear, carrier or affected. Carriers of the gene are heterozygous and do not develop the disease’s symptoms. When mating two carrier cats, each future kitten has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
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