Progressive retinal atrophy or degeneration (PRA or PRD) is the name for several diseases that are progressive and lead to blindness. It is found in over 100 breeds of dogs. It is an inherited condition and affects the retina of the eye.

Here is a very simple explanation of the process by which a dog "sees":   Light passes through the lens and is directed onto the retina, which contains specialized photoreceptor (light-sensitive) cells called rods and cones. These cells convert the light into electrical nerve signals, which pass along the optic nerve to the brain, where they are "translated" into images.

~ rods are responsible for vision in dim light i.e. night vision.

~ cones are responsible for vision in bright light i.e. daytime and color vision.

WHAT IS PRA?

Normally, the photoreceptors in the retinas develop after birth to about 8 weeks of age. The retinas of dogs with PRA either have arrested development (termed retinal dysplasia) or early degeneratation (deterioration) of the photoreceptors. Retinal Dysplastic dogs are usually affected within two months of birth and may be completely blind by one year of age. Retinal Degenerative dogs are affected from one year to eight years of age and the symptoms progress slowly.

WHAT ARE THE SIGNS OF PRA?

Signs may vary depending on the development of PRA and its type. The eye of an affected dog will look normal. PRA is also non-painful. You may start to notice signs of night blindness, which is characterized by not wanting to go down stairs or down a dark hallway. During the day it is as though their vision will seem normal or improved. After some progression you may notice pupil dilatation and reflection of light from the back of the eye. With some dogs the lens may look cloudy or opaque.

If PRA progresses slowly, you may not even notice the symptoms.

IS PRA TREATABLE?

Unfortunately, there is no cure or treatment for PRA, nor is there a way to slow the progression of the disease. Dogs seem to adapt to the progressive blindness and often perform normally in their environments. The blindness is more pronounced when the environment is changed.

CAN PRA BE DETECTED AND PREVENTED?

Depending on the form of PRA, characteristic changes in the retina can be observed by examination by a veterinary ophthalmologist and the dog can be certified as FREE thru the CANINE EYE REGISTRATION FOUNDATION (CERF).

But PRA has a genetic component. DNA is being used to identify which genes are responsible for PRA. Progressive Rod-Cone Dysplasia (PRCD), is the most widespread form of PRA. It is important to test your dogs at six months of age to identify if they are suffering from PRA.

PRCD starts with night blindness and progresses to total blindness at 3 to 5 years of age.

Researchers have developed a genetic test that identifies a set of genetic markers which usually indicate the presence of the gene mutation that causes this disease. Even though the exact gene has not been found, each and every dog affected has two copies of this genetic marker and every dog that does not carry these markers are clear of the disease. A carrier has only one copy of the defective gene and will not go blind, but it can pass on the gene to future generations. Currently there is no cure for PRA or PRD (prcd). The only way to avoid it is to perform the test on all your breeding stock in hope of avoiding breeding it into the offspring.

TESTING FOR PRA.

At present the testing is only available in the UK, by blood samples taken and submitted for testing to a specialized laboratory. Testing in the USA is still being developed. After blood sample is tested by a lab the dog can then be classified as normal, a carrier, or affected. Your breeding programs can be re-evaluated after the results have been received. Dogs that are tested Clear or Normal and Carriers can still be used for breeding but dogs tested as Affected should not be bred together.

INHERITANCE

The inheritance of PRA in a couple of breeds of dogs is known to be sex-linked, and it has a dominant form of inheritance in another couple of breeds. However, in the majority of breeds affected by PRA, the mode of inheritance is known or thought to be AUTOSOMAL RECESSIVE.

BREEDING ISSUES

Breeds with a genetic marker - (autosomal recessive mode of inheritance). The advantage of having a genetic marker for PRA is that breeders know the status of the dogs they are breeding, (if they are tested). This means that carriers, and even affected dogs, can be selectively used in the breeding program, without the risk of producing puppies that will eventually go blind as a result of PRA e.g.

SAFE mating with known status dogs, are those that produce only normal or carrier puppies i.e.

~ normal x normal 
~ normal x carrier 
~ normal x affected

UNSAFE matings with known status dogs, are those that can produce affected puppies, which will eventually go blind, i.e.

~ carrier x carrier 
~ carrier x affected 
~ affected x affected

CURRENT TEST BEING USED FOR DACHSHUNDS:

 Approximate Age at which diagnosis is possible, Dachshund (min. Long - haired) 5 months.

 The Narcolepsy � NARC - test is a DNA-based test that provides, for the first time, a method to unequivocally identify narcolepsy(pra) in several breeds Doberman Pinschers, Labrador retrievers and Dachshunds. This test allows you to control the narcolepsy (pra) gene frequency in your breed so as to prevent producing puppies affected with the disease.

An article by Mary M. Woodsen tells the story of how this test was developed. The article follows below, after the information on testing.

Reliable identification of dogs that do not carry disease genes is the key to controlling autosomal recessive diseases. The NARC test enables 100% accurate identification of these dogs. Called "genetically clear," "noncarriers" or, more formally, "homozygous normals," such dogs can pass only the normal gene on to all their pups, which means that none of their pups can ever be affected with narcolepsy. These "clear" dogs can be bred to any mate, even to a narcolepsy-affected dog which may be a desirable breeding prospect for other reasons.

Homozygous means both copies of the gene in your dog are the SAME - both normal or both NARC. A carrier has one normal and one NARC gene.

Because the NARC test is a mutation-based gene test, it accurately and specifically identifies normal dogs, carriers (heterozygous dogs) and affecteds. Possible test results are listed in the table below. Possible results using the NARC test.

This is the result that will be reported by the Narcolepsy test.

 N=
 Normal (Clear)
 Normal gene, so will never develop the disease
 
 C=
 Carrier
 Carries one disease gene, but will never develop the disease
 
 A=
 Affected
 disease gene and will develop the disease
 

Stay informed about updated with the latest news and information concerning the Dachshund breed.

Some of the above information has been repoduced from the Bregorrey Glens website.