PRA CORD1 MUTATION - Southern English Springer Spaniel Society
PRA CORD 1 MUTATION
ANNOUNCEMENT OF DNA TEST
A worldwide statement was issued on 20th April 2007 by Dr. Cathryn Mellersh from the Animal Health Trust (AHT) and Dr. Gary Johnson from the University of Missouri USA, stating that a mutation (known as the Cord1 mutation) has been identified that is a major risk factor for the development of one specific form of PRA in English Springer Spaniels. They also announced that a DNA test for this mutation has been developed and is now available in both the USA and UK. Other forms of PRA that may also exist in the Breed have not yet been genetically identified and can only therefore be detected by clinical eye testing.
Following that announcement, a number of breeders, who had donated samples from clinically affected dogs and their close relatives to the original PRA research project at the AHT, were invited to request from them the genetic results for these dogs.
These breeders had, naturally, expected that their clinically affected dogs would be confirmed as genetically affected, but when some results showed this not to be the case (i.e. their dogs tested as either genetically clear or carriers), considerable confusion and alarm ensued concerning the validity of the DNA test.
It is the opinion of both Dr. Mellersh and Dr. Johnson, that, barring any errors in the testing procedures, these unexpected genetic results can be explained by either of the following:
1) There is another form of PRA in the English Springer Spaniel caused by a different mutation in a different gene that, as yet, has not been identified. Different genetic forms of the same eye disease occurring in the same breed are not unheard of, and it is entirely possible that some dogs can carry either or both mutations.
2) In some rare instances, a dog can develop PRA as a result of carrying a single copy of the mutation (i.e. a genetic carrier), rather than two mutant copies as would be expected in affected dogs. This would be unusual, based on what is known, but cannot formally be excluded at this stage.
The original announcement (see below) made by Dr. Mellersh and Dr. Johnson, may, unintentionally, have given the impression that the new test was the whole answer with regard to PRA in the Breed. Whilst it certainly mentioned that a second form of PRA was a possibility, the figures quoted (which were based on statistics from the USA studies) suggested that a second form was probably rare. Dr. Mellersh was and still is unable to give any estimates or make any predictions as to which form of PRA is the most prevalent form in the UK. This is because she only has a very limited number of clinically ‘affected’ samples to work with, and these samples do not represent a random subset of the UK population.
The DNA test for PRA that has been made available is for one specific mutation in one specific gene (known as the ‘PRA Cord 1 Mutation’, which is a mutation in the RPGRIP1 gene), and the test cannot, therefore, detect any other mutation that may be responsible for any other form of PRA. It does not, however, diminish its validity for this particular mutation, which is undoubtedly associated with PRA in English Springer Spaniels.
To find a list of PRA Cord1 DNA test results, click on List of
To find test results for individual dogs, click on
Statistics from the AHT show that between 20 – 30% of dogs tested in the UK are genetic carriers for the Cord 1 (RPGRIP1) mutation, with approximately 3% being genetically affected. It should be noted that these figures were obtained using dogs NOT collected specifically for PRA research and thus represent a random cross section of the breed. Irrespective of whether a second form of PRA exists in the Breed, the prevalence of this mutation alone in the UK population is very significant.
The DNA test allows breeders to identify those dogs either carrying or affected by this mutation, and, through careful and sensible breeding over several generations, to eliminate it from their breeding. The fact that it is not the whole of the answer to PRA is, of course, disappointing, but the fact that a DNA test is available for any form of PRA has to be a step forward.
This new test, as with any other, is simply another tool that breeders now have at their disposal should they wish to make the most of the information available to them. When making decisions on breeding, the results of any test should be taken in the overall context of the merits or weaknesses of each dog and the severity or consequences of the disease to which the test relates.
With regard to PRA, it is the intention to carry out further research into both of the following areas:
a) The identification of the mutation that causes a second form of PRA in the Breed. This will require samples from dogs that are diagnosed as clinically affected but their DNA test shows that they are not genetically affected for the Cord 1 (RPGRIP1) mutation.
b) The identification of dogs that have been tested as genetically affected for the Cord 1 (RPGRIP1) mutation, but are not yet clinically affected. From a breeding point of view, it is the genetic status that counts, but Dr. Mellersh and Dr. Johnson have advised that other genes may influence the age of onset and rate of progression in dogs genetically affected for the Cord 1 (RPGRIP1) mutation, and further studies are required to explain this.
Individual owners and breeders whose dogs fall into either of the above categories, and who wish to donate a DNA sample to the research, are invited to contact Dr Cathryn Mellersh at the AHT to request a swab kit or more information.
ESS owners and breeders, who wish to do so, are encouraged to use the new DNA test for PRA Cord 1 in addition to continuing with clinical eye testing for all breeding stock.
ESS Breed Clubs Health Co-ordinators:
Lesley Bloomfield Tel: 01923 823579 Email:
Louise Scott Tel: 020 8427 3396 Email:
[Procedure for requesting a PRA Cord 1 DNA test CLICK HERE]