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Eye Clinic 2008

The OptiGen prcd-PRA Test

The OptiGen prcd-PRA test is a DNA-based test that helps you avoid one form of Progressive Retinal Atrophy (PRA). PRA refers to a group of diseases that cause the retina of the eye to degenerate slowly over time. The result is declining vision and eventual blindness. “prcd” stands for “progressive rod-cone degeneration” which is the type of PRA known in several breeds.

PRA Disease

The genetic disorder, prcd-PRA , causes cells in the retina at the back of the eye to degenerate and die, even though the cells seem to  develop normally early in life. The “rod” cells operate in low light levels and are the first to lose normal function. Night blindness results. Then the “cone” cells gradually lose their normal function in full light situations. Most affected dogs will eventually be blind. Typically, the clinical disease is recognized first in early adolescence or early adulthood. Since age at onset of disease varies among breeds, you should read specific information for your dog. Diagnosis of retinal disease can be difficult. Conditions that seem to be prcd-PRA might instead be another disease and might not be inherited. OptiGen’s genetic test assists in making the diagnosis. It’s important to remember that not all retinal disease is PRA and not all PRA is the prcd form of PRA. Annual eye exams by a veterinary ophthalmologist will build a history of eye health that will help to diagnose disease.

Unfortunately, at this time there is no treatment or cure for PRA. If your dog is affected, you may find it helpful to read about other owners’ experiences living with blind dogs. (suggested links: www.eyevet.org and www.blinddogs.com )

Inheritance

Prcd-PRA is inherited as a recessive trait. This means a disease gene must be inherited from each parent in order to cause disease in an offspring. Parents were either “carrier” or affected. A carrier has one disease gene and one normal gene, and is termed “heterozygous” for the disease. A normal dog has no disease gene and is termed “homozygous normal” – both copies of the gene are the same. And a dog with two disease genes is termed “homozygous affected” – both copies of the gene are abnormal.

It’s been proven that all breeds being tested for prcd-PRA have the same disease caused by the same mutated gene. This is so, even though the disease might develop at different ages or with differing severity from one breed to another.

Although prcd-PRA is inherited, it can be avoided in future generations by testing dogs before breeding. Identification of dogs that do not carry disease genes is the key. These "clear" dogs can be bred to any mate - even to a prcd-affected dog which may be a desirable breeding prospect for other reasons. The chance of producing affected pups from such breedings depends on the certainty of test results. Again, you’ll find the specific information on certainty of test results for your dog by linking to breed specific information.

 The Genetic Test

The OptiGen prcd test is done on a small sample of blood from the dog. The test analyzes the specific DNA mutation causing prcd-PRA. The OptiGen test detects the mutant, abnormal gene copy and the normal gene copy. The result of the test is a genotype and allows separation of dogs into three groups: Normal/Clear (homozygous normal), Carrier (heterozygous) and Affected (homozygous mutant).

How you can participate

The prcd-PRA test is done on a small sample of blood obtained by your veterinarian. This allows the lowest risk of contamination of the sample and added assurance of a match of the sample with the identified dog.  Please contact Maureen D'Arcy (Secretary) for i nformation details

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