| 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
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
|
| Possible results using the OptiGen prcd test | |||
| Pattern/Genotype* | Risk Group | Significance For Breeding | Risk For Developing prcd |
| A | I. Normal | Can be bred to any dog | Will never develop prcd |
| B | II. Nonaffected | Probably a carrier of prcd | Will never develop prcd |
| C | III. High Risk | Probably homozygous for prcd | Probably will develop prcd |
| * This is the result that will be reported when a dog is tested using the Optigen prcd test. | |||
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 read Instructions and Information to learn about ordering a test, shipping a sample and prices.Affected dogs are tested at no charge. Please review the conditions for this before submitting a sample from an affected dog.
Registries: Breed clubs may sponsor genetic disease registries and OptiGen may provide some test information directly to the registry in accordance with the club’s official policies. Please go to your club to learn more about this.
The research leading to this discovery was undertaken by scientists at the James A. Baker Institute of Animal Health at Cornell University's College of Veterinary Medicine in Ithaca, New York. Initial data are published in volume 95 of the March, 1998 issue of the Proc. National Academy of Sciences. Publication of the prcd mutation is being prepared. The patented technology underlying this test is under exclusive license to OptiGen from Cornell Research Foundation, Inc.
| Breeding Strategies for
prcd-PRA Test:
This table highlights all the desirable breedings that include at least one Normal/Clear parent. All other breedings are at risk of producing Affected pups with an extremely high probability of developing prcd during their lifetime. However, all dogs can be bred safely. It isn't necessary - or even desirable - to remove dogs from the breeding population. But when choosing pups to retain as potential breeding stock, it is important to select for Normal/Clear dogs and select against Affected dogs. |
| Expected results for breeding strategies using the OptiGen prcd test | |||
| Parent
1
Pattern/Genotype |
Parent 2 Pattern/Genotype | ||
| A | B | C | |
| A | All = Pattern A | 1/2
= Pattern A
1/2 = Pattern B |
All = Pattern B |
| B | 1/2
= Pattern A
1/2 = Pattern B |
1/4
= Pattern A
1/2 = Pattern B 1/4 = Pattern C |
1/2
= Pattern B
1/2 = Pattern C |
| C | All = Pattern B | 1/2
= Pattern B
1/2 = Pattern C |
All = Pattern C |
Benefits & Limits to All Genetic Testing:
The benefits of genetic disease testing are clear. With informed breeding practices, breeders immediately can avoid producing affected pups, yet use any dog in their program regardless of genetic disease status. And since genetic testing can be done at any age, each dog’s genetic status can be known before clinical disease signs are recognized. Over several generations of selection away from the disease gene, breeders can even eliminate a disease gene completely from their line.BUT, there are basic limits for any and all DNA genetic tests. Whether a test is mutation-based or marker-based, it identifies only the specific mutation being tested or the association between a specific marker set and the disease. For example, a mutation test detects one specific mutation in one specific gene. If there are several different mutations or several different genes that can cause the same condition, one must discover and then test for each mutation and each gene. Likewise, a marker test uses one marker or set of markers to define a specific condition. If the condition is associated with several different marker combinations, one must discover and then test for each marker combination. It can be difficult or even impossible to know how many mutations or how many marker sets exist in all the members of a specific breed. As more and more dogs are tested, previously unknown variations may come to light.
In the case of PRA, also keep in mind that not all retinal disease is PRA and not all PRA is the form currently detectable in your breed. Accurate diagnosis is essential. A dog can test as normal or carrier, yet be affected by a different type of PRA. Although more than one type of retinal degeneration probably occurs in every breed, by far the most common type of PRA for your breed is the type currently being tested by OptiGen.
Additional Points:
The OptiGen prcd test can be done reliably at any age – even in young pups, and the result will be the same at any age, and will be the same whenever it is repeated.
Since most breeds are affected with other inherited eye diseases, we recommend that yearly eye examinations by a board certified veterinary ophthalmologist be continued, for example, through the CERF program in the U.S. or similar program elsewhere. However, a normal exam in a young dog cannot rule out PRA at a later age. To establish PRA affected status by ERG, it is necessary that a full diagnostic protocol be done with dogs under anesthesia or heavy sedation, and that the rod and cone contributions of the ERG be separately evaluated.
Tallies of test results are updated and provided quarterly to national breed clubs, at their request.
