Genetic PRA Test

OptiGen LLC
Cornell Business and Technology Park
33 Thornwood Drive, Suite 102
Ithaca, NY 14850
Telephone: 607.257.0301
Fax: 607.257.0353

The OptiGen prcd test is a DNA-based test that provides, for the first time, a method to eliminate Progressive Retinal Atrophy, or PRA, from the Chesapeake Bay Retriever - thereby controlling the prcd gene in the breed's gene pool.

Reliable identification of dogs that do not carry disease genes is the key to eliminating autosomal recessive diseases. The OptiGen prcd test provides 100% accurate identification of these dogs. Called "genetically clear", "noncarriers" or, more formally, "homozygous normals," such dogs can only pass the normal gene on to all their pups - which means that none of their pups can ever be affected with prcd. These "clear" dogs can be bred to any mate - even to a prcd-affected Chesapeake Bay Retriever 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 prcd. A carrier has one normal and one prcd gene.

The OptiGen prcd test is a marker test rather than a mutation-based gene test. This means that it identifies dogs by a "fingerprint" on chromosome 9 near the prcd gene locus, rather than by detecting the prcd mutation itself. The result of the test is a genotype or pattern - a fingerprint - that allows the separation of Chesapeake Bay Retriever into three groups: pattern/genotypes A, B and C.

Possible results for a Chesapeake Bay Retriever using the OptiGen prcd test

Pattern/ Genotype * Risk Group Significance For Breeding Risk For Developing prcd

A I. Normal Can be bred to any CBR 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 CBR is tested using the OptiGen prcd test.

Some uncertainties remain about the risk for dogs with Pattern B and C. But this doesn't reduce the value or reliability of the prcd test in evaluating a Chesapeake Bay Retriever as a breeding prospect. Most "B" dogs are carriers for prcd, though a small percentage are not. None, however, are or will become affected by prcd. All "B" dogs should only be bred to "A" mates. All "C" dogs are homozygous for markers associated only with prcd, and most will develop PRA. These dogs should also be bred only to "A" 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

This table shows that all the desirable breedings include at least one parent with Pattern A genotype from the OptiGen prcd test. All other breedings are at risk of producing pups of Pattern C, with a high probability of developing prcd. 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 dogs with Pattern A genotype - and select against dogs with Pattern C genotype.

How you can participate...

The PRA Test for Chesapeake Bay Retriever is done on a small sample of blood. The fee of $260 (paid in advance) includes a confidential report and certificate of results. An additional $35 fee archives your dog's sample for 10 years for use in other tests. Email us, or call us to get specific information and instructions before having blood samples sent to OptiGen. Sample and packaging requirements may differ for domestic and international shipments.

The research leading to this discovery was undertaken by scientists at the James A. Baker Institute for Animal Health at Cornell University's College of Veterinary Medicine in Ithaca, NY, and published in volume 95 of the March, 1998 issue of the Proc. National Academy of Sciences.The patented technology underlying this test is under exclusive license to OptiGen from Cornell Research Foundation, Inc.

Saying it another way...prcd-PRA test interpretation
The following statements can help you to interpret your results.

All dogs yielding Pattern A are homozygous normal. This result is certain and can be determined from birth. No Pattern A dog will ever pass the prcd mutant gene to a pup. No pup of a Pattern A dog can be affected with the prcd form of PRA, regardless of the status of the other parent. There is no longer a need to have regular eye exams for PRA and/or ERGs on pups from Pattern A dogs since they cannot develop PRA. Of course, this does not remove the need for or value of eye exams to detect disease other than PRA.

No dogs yielding Pattern A or B will ever develop PRA. This result is certain and can be determined from birth. Thus, for dogs at risk from family history of developing PRA, you can identify which dogs cannot be affected. There is no longer a need to have regular eye exams for PRA and/or ERGs on Pattern A or Pattern B dogs since they cannot develop PRA. Of course, this does not remove the need for or value of eye exams to detect disease other than PRA.

The only dogs at risk of developing PRA are Pattern C dogs. Thus, these are the only dogs for which it makes any sense to have ERGs.

All PRA affected dogs yield Pattern C. This result is certain, and can be used to eliminate possible incorrect or uncertain clinical diagnoses. If a dog is considered "suspicious" of PRA, or diagnosed as affected, then it must be Pattern C for it to be truly affected with PRA. If it is either Pattern A or B, it cannot be affected with PRA.

Remember, genetic tests can be done reliably at any age, and the results are exactly accurate. That is, the test result will never change with age and will be the same whenever it is repeated.

Regarding DNA tests on frozen semen, in fact the sperm DNA can be tested. Each sperm is haploid - one half the chromosome set - however, there is a mix of the "two types" among all the sperm, so the test is done on DNA extracted from lots of sperm and then it correctly represents the total chromosome picture. At present, OptiGen is not ready to do DNA extraction on semen-sperm, but it can and will be available in the near future.