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 atrophy
Cats can also develop vision loss if their diet is deficient in the amino acid taurine. PRA secondary to taurine deficiency starts in the central portion of the retina. As a result, cats with taurine-deficiency PRA have difficulty seeing with their central vision but their peripheral vision is intact. Taurine-deficiency can occur if a cat is being fed a diet not specifically formulated for cats, such as dog food or a homemade diet. Fortunately, taurine-deficiency PRA advances slowly and switching to the right diet can halt progression.

Diagnosis of progressive retinal atrophy
If it looks like your cat is having trouble seeing, you should take her to the veterinarian as soon as possible. Your veterinarian can usually diagnose PRA based on the appearance of your cat’s retina. Electroretinography or genetic testing may be ordered to confirm the diagnosis.

Treatment of progressive retinal atrophy
Unfortunately, there is no treatment for PRA due to a genetic mutation. However, scientists have identified 2 of the genes that cause PRA in cats, allowing breeders of predisposed breeds to check their breeding stock with these genetic tests. For fluoroquinolone-associated PRA, it is important to discontinue the antibiotic as soon as possible to avoid additional damage to the retina. With taurine-deficiency PRA, correcting the nutritional deficiency promptly stops the progression.

Living with progressive retinal atrophy
It’s important for people to understand that cats can adjust remarkably well to living with PRA. Unlike people, cats don’t need to drive or read and they spend most of their time in one place. As a result, cats become familiar with the layout of their house and can get around easily by memory. However, there are a few things you need to know if you are living with a blind cat:

  • Try not to rearrange furniture
  • Keep blind cats away from pools and balconies without barriers

I have personal experience with feline progressive retinal atrophy (2 of my cats have had it). Both cats lived long happy lives. Most people who met my cats didn't even realize they were blind and were amazed to see them maneuver around my house and even jump onto the furniture.

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.


Product Description

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.

Genetics

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.


Progressive retinal atrophy

Progressive retinal atrophy is the term used to describe a group of genetic disorders that result in degeneration and atrophy (loss or wasting) of the retina – the light-sensitive layer of cells at the back of the eye. This can lead to a progressive decline in the quality of vision and in some cases can lead to blindness. The human equivalent of this disease is known as ‘retinitis pigmentosa’.

Owners may become aware of this condition when vision becomes significantly impaired and, for example, the cat may start to become disorientated or bump into objects.


Retinal Degeneration

Progressive Retinal Atrophy

Progressive retinal atrophy (PRA) is an inherited condition which causes gradually progressive degeneration of the retina with irreversible blindness. In all breeds in which the type of inheritance has been identified, it is autosomal recessive. This means that each parent must carry an abnormal gene and that two parents who are not affected themselves may produce affected puppies.

The age of onset and rate of progression varies from breed to breed. Usually, the vision becomes affected when the dog is 6-8 years of age. The first sign typically observed by an affected dog’s owner is loss of night vision. Behavioral changes attributable to vision decline progress over several months to years until daylight vision is also noticeably affected and many dogs eventually go blind.

While early stages of PRA may be more difficult to diagnose, most dogs with PRA that are presented for vision loss already have advanced disease and the diagnosis can be made easily at an exam by an experienced veterinary ophthalmologist using indirect ophthalmoscopy. Thinning of the retina with an associated increase in the “shininess” of the reflective tapetum are observed, along with reduced size of the retinal vessels. Examples of advanced retinal degeneration is seen in photographs on this page.

Occasionally, cataracts may occur secondary to late stage retinal degeneration. In such cases, cataract surgery is obviously of no benefit. However, often a dog may not present for ophthalmic examination until the cataracts have progressed so that detailed examination of the retina is prevented by the cloudy lens. In such cases, electroretinography is essential to diagnose the retinal disease and prevent an unnecessary (and unsuccessful) cataract surgery. An electroretinogram measures the electrical response of the retina in response to light stimulation. Even in the presence of a corneal opacity or cataract, sufficient light reaches the retina to result in a response demonstrating whether the retina is functional.

For even more information, here is a brochure on PRA provided by the American College of Veterinary Ophthalmologists.

Sudden Acquired Retinal Degeneration

Although most cases of retinal degeneration are inherited, there is a spontaneous (non-inherited) syndrome of rapid onset, bilateral, retinal degeneration called Sudden Acquired Retinal Degeneration Syndrome (SARDS). Affected animals present for sudden blindness and dilated pupils, yet have an otherwise unremarkable eye exam. Retinal degeneration must be proven using a special test called an electroretinogram in these cases.

For even more information, here is a brochure on SARDS provided by the American College of Veterinary Ophthalmologists.

Other Tests, Treatment, and Outcome

While the diagnosis of retinal degeneration is made by ophthalmoscopy and/or electroretinography, genetic testing for PRA can be useful for breeders to identify not only affected animals, but those that are genetic carriers for the disease. This type of diagnosis is essential to eliminate carriers from the breeding population. For more information on genetic testing, visit Optigen.com.

Unfortunately, there is no proven treatment for any form of retinal degeneration. These conditions are painless and, in most cases, loss of vision progresses slowly and pets adjust to this handicap remarkably well. Animals which are irreversibly blind can live a normal lifespan and have an excellent quality of life provided some extra care by their owners. It is important to recognize that loss of vision does not represent the same handicap for our pets as it would for us. For us, blindness would mean an inability to read or drive a car and a loss of independence. Our pets are already (happily) dependent on us. It is important to keep their environment as safe as possible. A harness may work better than a collar for guiding your pet on walks outdoors — a blind pet should never be allowed to run free. Try not to rearrange the furniture and you will be amazed at how well your pet will remember the floor plan — even going up and down stairs. Swimming pools and balconies present particular hazards and some sort of barrier may be necessary in these situations. A blind pet can continue in every way in their primary role as a loving companion. Learn more here about helping a blind pet adjust.


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Progressive Retinal Atrophy (PRA) is an inherited, late-onset blindness found in Abyssinian, Somali and Ocicat breeds. The disease has also been observed in Siamese and related breeds and poses a significant health risk in these breeds. Other cat breeds at risk are Javanese/Balinese and Oriental Shorthair. Bengal cats, American wirehair, Tonkenese and American curls are at lower risk.

It is typically characterised by a progressive degeneration of photoreceptors in the eye. A mutation in a gene called CEP290 has been found to be associated with PRA in the above mentioned breeds.

It is normal for photoreceptors to develop after birth to about 8 weeks of age. However in kittens affected with PRA, the photoreceptors develop, but as the cat ages, the photoreceptors degenerate, leading initially to night blindness and progressing to total blindness at around 3-5 years of age.

PRA is inherited as an autosomal recessive disorder, meaning that two copies of the mutation are needed for the disease to occur. Carriers of only one copy of the mutation are not affected and will have normal vision.

A simple cheek swab will enable breeders to identify both carriers and affected animals and plan breed programs accordingly.

CEP290 Mutation Not Found / Carrier / Affected

NB: Other causes of PRA may exist which are not identified by this test.

Interpretation

Not found = The CEP290 mutation was not found.

Carrier = One copy of the CEP290 mutation was found. Such cats are carriers but
will not be affected and will have normal vision. Precautions should be taken in breeding programs.

Affected= Two copies of the CEP290 mutation were found and PRA is likely to
develop.

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