health
Presentation on PRA (Progressive Retinal Atrophy) in DogsAuthor’s Note
Before you read this article I would like to point out that it has been proved that PRA in Gordons is late onset and although it is a good idea to have your dogs tested early, a clear eye test can not exclude PRA in later life. Tony Wall did not have all the information at has fingertips at the time of the presentation.
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On the morning of the GSCS AGM 2010 there was a very interesting presentation by Tony Wall who is one of the few eye specialists we have in Scotland. He has been on the KC eye panel since 1983 and has also been interested in other species for over 10 years. He very kindly came down from Inverness to speak to us. The presentation was well attended by doggie people and was not restricted to Gordoners.
As you all must know by now late onset PRA has been found in a few Gordons. It is carried on a recessive gene and that means that both parents must be carriers in order for the condition to be inherited. If both parents are carriers there is a 1 in 4 chance with each pup that it will inherit the disease. This is the same with every recessive gene whether it be something that will not affect the dogs health like the colour Red, or Liver and Tan, to some devastating human diseases like Cystic Fibrosis. Fortunately Gordons seem to be clear so far of other devastating genetic diseases.
He was just as interested as us in the fact that PRA has been found in Gordons because he personally has not seen a case and mentioned that the very first case of PRA ever described in any breed was in a Gordon Setter in Norway in 1911. Since then it was thought that the breed has been clear of the disease. He quite rightly asked where did it go? It was not mentioned the age of this particular dog so whether it was late onset is unclear. He recommends testing dogs at a much earlier age beginning at 2 years old to find out if it truly is late onset or is just not being found till later. Given the fact that dogs seem to blind relatively quickly when the disease process starts the probability is that it is late onset. We do need to find out for sure and as many dogs as possible must be eye tested early for the good of the breed. If a dog is tested clear at a young age it does not mean that the dog is clear it means that it is showing no signs and it must be tested again when older. As I understand it this is to find out if the disease is in fact truly late onset and presumably will not be necessary when we have a gene test.
The presentation began with the showing of some very interesting slides of both normal and diseased retinas, and gave us a little insight into just how devastating PRA can be. A normal healthy retina collects information and transmits it to the optic disc which then transmits the information along the optic nerve to the brain. A dog has a much more shiny retina than a human and information is also reflected back to provide additional information for the nerves to interpret. In a healthy eye this retina has lots of healthy blood vessels but in one slide they had all but disappeared and the whole retina was more like a polished mirror. That poor dog (not a Gordon but could easily have been) was well on its way to total blindness.
PRA affects both the Rods and Cones with degeneration of the retinal nerves. There is no cure and the dog will go blind and it always affects both eyes. At present we seem to be finding out that a dog is affected when it is actually going blind but there are signs that are detectable before the sight is noticeably affected. Tony Wall thinks that we should be getting our dogs looked at earlier to make sure that it is in fact as late onset as we think it is. He did not know how early it could be detected as we are still feeling our way. Meanwhile if you have an older dog the first sign of loss of sight is a reluctance to go out at night because night vision is the first thing to go. There is also a greater reflectivity in the eyes and then day vision deteriorates and the dog develops secondary cataracts. The only way to tell if all these things are due to PRA and not some other eye condition is to have the dog looked at by an eye specialist and you are all encouraged to do this for the good of the breed especially if the dog has progeny. We must all be open about this if we are to eliminate this devastating condition.
Unfortunately at present we have not got a genetic test to find out which dogs are carrying the gene but there are hopes that this will soon be found. Meanwhile because the disease is not being detected until about 8 years of age the chances are that the dog or bitch will already have progeny by the time it is diagnosed. This is not as disastrous as it sounds because if the dog has been mated to a genetically clear dog then the offspring will all be carriers but not clinically affected. The value of having a genetic test then becomes very obvious because in the absence of clinical signs it will be possible to know which dogs will be affected and which dogs are carriers. Tony Wall was very clear that in the absence of a large gene pool we should be careful about discarding potential breeding stock purely on the result of a gene test because of the risk of narrowing the gene pool even more and perhaps creating different genetic problems in the future. Therefore breeding must be done carefully but not blindly (forgive the pun) and with care we could eventually eliminate the disease. Being a carrier of any recessive gene whether it be for colour or disease is not a sufficiently good reason to discard a dog from a breeding program if otherwise it has all the features to make a good and healthy Gordon. We must never mate carriers to carriers or carriers to affected stock but with careful management and a reliable gene test it would be possible to eliminate the problem in a few generations but there is a danger in trying to make it happen too fast and ending up with a different (and worse) problem. Tony Wall was very clear on this point that we must not discard otherwise good stock purely on the grounds that it is a carrier. I do remember some daft hysteria about people refusing to use carriers of the liver gene in their breeding programme and that was not even a health risk so I can only imagine people getting paranoid about this gene and narrowing our gene pool still further. He emphasised that other potential and just as harmful or even more harmful diseases could appear if we narrow our gene pool even further and was emphatic that we must look at the whole dog and not just this one gene.