Progressive retinal atrophy - its days are numbered

FROM the United States there is good news on research to trace the gene responsible for progressive retinal atrophy (PRA) in all affected breeds. From October 1999 the test has been available for the Labrador retriever, bringing to six the number of breeds in which the presence of the gene for PRA, and its dominant or recessive form, can be recognised.

The other five breeds are Portuguese water dogs, Chesapeake Bay retrievers, Irish setters, English cocker spaniels and Cardigan Welsh corgis. International testing is now offered for a number of other genetic diseases and the future identification of most looks certain.

Tests are available for canine leucocyte adhesion deficiency (CLAD), congenital stationary night blindness (CSNB), phosphofructokinase (pfk) deficiency, pyruvate kinase deficiency, copper toxicosis, renal dysplasia and von Willebrand's disease(vWD), and the list of breeds is growing all the time.

The companies that carry out the testing are OptiGen, of Ithaea, New York, which has an exclusive licence to test the Chesapeake Bay retriever, English cocker spaniel and Portuguese water dog for PRA (All other tests, it seems, are in the public domain and are being developed at an ever-increasing pace); VetGen, of Ann Arbor, MI; and GeneSearch, of Rockville, MD.

The test results reveal whether the animal is affected with the disease, is a carrier of the disease, or is clear. Based on individual test results, breeders will then be able to work towards the elimination of the target disease or diseases.

In the wake of identification of the rogue genes it is easy to look into the future and see a time when there may be no genetic diseases remaining to make the lives of many of our faithful companions uncomfortable at best, and a living hell at worst. Elimination of genetic diseases is likely to be slow, but the pace will ultimately depend on the breeders. They will not need to stop breeding their carrier stock, or even their affected stock if these animals have attributes that are worth preserving in their lines. The mating rules as stated in OptiGen's breeding chart allow affected or carrier dogs to be mated, but only to clear dogs. A clear dog can be mated to any of its breed.

No pup bred from a clear dog can ever be affected with PRA, no matter what the status of the other parent. And no clear or carrier dogs will ever develop PRA. From this information breeders will see that if, in every future mating, one of the parent dogs was certified clear, there would be no chance of an unexpected genetic disease-affected dog 'popping up' in any litter, other than through uninformed or accidental matings.

Testing seems a small inconvenience in order to gain such a huge advantage. GeneSearch is offering the tests at much lower cost than either OptiGen or VetGen. Its prices for PRA in the Irish setter and Cardigan Welsh corgi (Labrador tests are at present under development)are $US40 as against OptiGen's $US135 for the Irish setter and $US260 for the Labrador retriever. Mary H Whiteley PhD at GeneSearch said her company intends to keep the tests affordable way genetic diseases will be eradicated is to make the tests affordable to all.

For New Zealand breeders there will be the added cost of the taking of the blood by the vet, its special packaging to reach the United States in good order and the freight costs - but considered over-all, the advantages will make light of any cost.

Clear dogs will obviously be highly sought-after for breeding purposes and those with affected or carrier dogs will be able to plan future matings with stock improvement as their goal. Expensive as the tests still are for those not residing in the US, we are sure to see New Zealand's first tested animals advertised this year and a groundswell will undoubtedly follow. A new era in canine health has been initiated and well-informed breeders will want to know the truth of their dogs' PRA (or any other genetic disease) status, whatever that truth is.

The following chart shows which tests are available, at which company and their cost:

(Updated as at December 24, 1999. As further developments may have been made since then, it is advisable to cheek the company websites for new information before sending blood samples.)

* Tests so marked are linkage tests - a 'marker' gene is identified, rather than the disease gene.

The collection and transport of blood samples for the above tests is subject to a number of requirements. Your veterinarian will need to collect the blood from your stock and it then must be treated according to specifications of the company doing the tests. A list of requirements should be obtained before taking the blood, so that there are no mistakes that could lead to blood having to be discarded and taken a second time. Generally, 3ml of blood must be taken from each test dog. Syringes must be new, not resterilised, and blood must be put straight into an anti-coagulant tube. Blood that is clotted can not be used.

If you air freight the samples there are special requirements designated by the air company, but if a courier firm is used inside the USA, instead of the USA Postal Service, each company has its own rules on how laboratory specimens are to be packaged and handled for their safe arrival. Make sure you and your vet know exactly what is required before you begin.