EXPLAINING PROGRESSIVE RETINAL ATROPHY
Progressive retinal atrophy (PRA) is the collective term for a group of inherited diseases of the retina. All of which are incurable and invariably lead to total blindness. PRA is known to affect many breeds of dog and characteristics such as the age at which with the disease progresses can vary from breed to breed. In some breeds the age of onset is very early but with other breeds, dogs may not start to go blind until they are well into middle age, or even older. In the UK it is a late onset form of PRA that our lovely breed appears to suffer from, now called PRA rcd4 for which the Animal Health Trust UK offer a simple mouth swab test to identify either Clear, Carrier or Clinically Affected dogs. There is evidence also that another less common mutation exists for which there is yet no DNA test, this type manifests itself much earlier. It is therefore imperative to continue with regular eye testing on your stock, even if you have a clear DNA result with the rcd4 test.
The carriers can still be used in a breeding programme so long as they are only ever mated with a DNA tested clear dog. That way breeding blind dogs is avoided, and dogs which have many other excellent attributes are still kept in the gene pool. Gradually the disease will be eliminated, as we endeavour to keep the clear dogs and use the registration endorsement 'not to be used for breeding' to protect the future Gordon Setter.
PRA is usually caused by an autosomal recessive mutation. This means that a dog must inherit two copies of the mutation, one from its sire and one from its dam for it to be affected. It also means that both parents of an affected dog must be carriers. If a dog inherits a single copy of the causal mutation from either of its parents and a normal copy of the same gene from the other parent then it will be a carrier. A CARRIER will NEVER develop PRA during its lifetime but would pass the mutation on to approximately half its offspring.
If the dog inherits two copies of the mutation it will develop PRA, but its eyes will be healthy until it reaches the ‘age of onset’ and clinical signs begin to develop. If an ophthalmologist examines a genetically affected dog before it begins to display clinical signs he/she will not be able to tell if the dog is affected and the dog will receive a clear eye certificate. An ophthalmologist can only tell a dog is genetically affected once the clinical signs of PRA have begun to develop. Then to further confuse us, secondary cataracts can also develop, frequently the local vet will attribute the early blindness to cataracts and the real cause is overlooked.
RECOGNISING PRA
It was in 2008 that I realised that there was definitely a problem with Will’s eyesight, (Kewstoke Apprentice) he was then eight years old. Up until then I had been unaware that the disease PRA was such an issue in dogs. Interestingly, he had a clear eye certificate when tested at Crufts, the last time when he was 5 years old, there had been no indication of PRA then.
His initial symptoms were unwillingness to go outside at dusk or night and unusually for him, panic when faced with a dim situation on a walk, heavy shading in woodland would spook him. He simply refused to walk in places like that. When he was 9 years old all he could see were moving shadows, within 18 months, even in the brightest sunlight he walked into every obstacle, his degree of vision reduced to zero. Apart from his blindness he was a healthy and strong dog.
Progressive retinal atrophy (PRA) is the collective term for a group of inherited diseases of the retina. All of which are incurable and invariably lead to total blindness. PRA is known to affect many breeds of dog and characteristics such as the age at which with the disease progresses can vary from breed to breed. In some breeds the age of onset is very early but with other breeds, dogs may not start to go blind until they are well into middle age, or even older. In the UK it is a late onset form of PRA that our lovely breed appears to suffer from, now called PRA rcd4 for which the Animal Health Trust UK offer a simple mouth swab test to identify either Clear, Carrier or Clinically Affected dogs. There is evidence also that another less common mutation exists for which there is yet no DNA test, this type manifests itself much earlier. It is therefore imperative to continue with regular eye testing on your stock, even if you have a clear DNA result with the rcd4 test.
The carriers can still be used in a breeding programme so long as they are only ever mated with a DNA tested clear dog. That way breeding blind dogs is avoided, and dogs which have many other excellent attributes are still kept in the gene pool. Gradually the disease will be eliminated, as we endeavour to keep the clear dogs and use the registration endorsement 'not to be used for breeding' to protect the future Gordon Setter.
PRA is usually caused by an autosomal recessive mutation. This means that a dog must inherit two copies of the mutation, one from its sire and one from its dam for it to be affected. It also means that both parents of an affected dog must be carriers. If a dog inherits a single copy of the causal mutation from either of its parents and a normal copy of the same gene from the other parent then it will be a carrier. A CARRIER will NEVER develop PRA during its lifetime but would pass the mutation on to approximately half its offspring.
If the dog inherits two copies of the mutation it will develop PRA, but its eyes will be healthy until it reaches the ‘age of onset’ and clinical signs begin to develop. If an ophthalmologist examines a genetically affected dog before it begins to display clinical signs he/she will not be able to tell if the dog is affected and the dog will receive a clear eye certificate. An ophthalmologist can only tell a dog is genetically affected once the clinical signs of PRA have begun to develop. Then to further confuse us, secondary cataracts can also develop, frequently the local vet will attribute the early blindness to cataracts and the real cause is overlooked.
RECOGNISING PRA
It was in 2008 that I realised that there was definitely a problem with Will’s eyesight, (Kewstoke Apprentice) he was then eight years old. Up until then I had been unaware that the disease PRA was such an issue in dogs. Interestingly, he had a clear eye certificate when tested at Crufts, the last time when he was 5 years old, there had been no indication of PRA then.
His initial symptoms were unwillingness to go outside at dusk or night and unusually for him, panic when faced with a dim situation on a walk, heavy shading in woodland would spook him. He simply refused to walk in places like that. When he was 9 years old all he could see were moving shadows, within 18 months, even in the brightest sunlight he walked into every obstacle, his degree of vision reduced to zero. Apart from his blindness he was a healthy and strong dog.