PRA (Progressive Retinal Atrophy) is an inherited eye disease found in many breeds of dogs with varying ages of onset. There are various types of PRA but the one most commonly seen in Cockers is GPRA (General Progressive Retinal Atrophy) also known as prcd-PRA.
Dogs with PRA will loose their eyesight and become totally blind. For more information about Progressive Retinal Atrophy (PRA) please click visit our PRA page and our hereditary eye disease page.
A DNA test (genetic fingerprint) is available; the test is marketed through the American company OptiGen. The OptiGen PRA test for Cockers looks for the gene mutation responsible for causing prcd-PRA (Generalised Progressive Retinal Atrophy). Dogs tested as "Normal/Clear" do NOT carry the mutation and therefore they are unable to pass the disease onto their offspring.
If the parents are not DNA tested please ensure that at the very least, they have been screened by the KC/BVA Eye Testing Scheme and the test results for the dogs are current (carried out within 12 months of the date of the pups birth). PRA is a progressive disease, the fact that a dog obtains a clear result the first time he/she is examined by a veterinary ophthalmologist does not mean he/she will be certified unaffected at a subsequent eye examination.
Be very wary of breeders who do rely solely on the KC/BVA scheme unless they have current certificates for the parents of their puppies. You should also note that the KC/BVA scheme does not detect carrier animals, all the test can say is that at the time of examination, the dog being tested is not currently affected by PRA, this does not mean he/she is not a carrier who could pass the disease onto offspring or indeed that he/she is not affected but yet to show symptoms.
There is no excuse for not DNA testing dogs used for breeding or breeding from dogs whose genetic status is not known through parentage!
DNA Testing
In late 2003/early 2004, the American company OptiGen developed a DNA test for the most common form of PRA found in Cocker Spaniels - prcd-PRA. The test at the time was not a mutation test, it was a "marker" test that detected changes in coding sequences of genes located near to and inherited with (linked to) the prcd gene. Dogs tested using the marker test, will have test results showing A1, B1 or C1, dogs tested using the gene mutation test with have Normal/Clear, Carrier or Affected results.
In June 2005 the American company OptiGen found the gene mutation responsible for prcd-PRA and ceased using the marker test. They also reduced the cost of the test to approx. £100 per dog (when using a 20/20 clinic and requesting the test online).
The OptiGen prcd-PRA test is performed on a small sample of blood from the dog. The DNA is analysed for the gene mutation. The result of the test is a genotype - a fingerprint - that allows separation of dogs into three groups for Cocker Spaniels: Genotype Normal/Clear, Carrier and Affected.
The option of a cheek swab (Buccal Cheek Swab) has now been added (for commercial reasons), however OptiGen do not recommend this method due to the risk of cross contamination. Our personal feelings are that the risk of cross contamination is too common with DNA samples derived from cheek cells and we personally prefer to continue with testing via blood samples. The risk of cross contamination (from other dogs in our household) is totally removed and we can be sure that the results for our dogs are from their DNA and not their household companions!
The DNA from the blood sample (or epithelial cells from the cheek) is analysed for the gene mutation. The result of the test is a genotype - a fingerprint - that allows separation of dogs into three groups for Cocker Spaniels: Normal/Clear, Carrier and Affected.
Possible results using the OptiGen prcd-PRA test: |
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| Genotype | Risk Group | Significance For Breeding | Risk of FN Disease |
| Homozygous Normal | Normal/Clear | Can be bred to any dog. Will never produce affected pups. | Will never develop prcd-PRA |
| Heterozygous | Carrier | Should be bred to Normal/Clear partners to remove the risk of producing affected | Will never develop prcd-PRA |
| Homozygous Mutant | Affected | Should be bred to Normal/Clear partners to remove the risk of producing affected | Very high risk of developing prcd-PRA |
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Expected results for breeding strategies using the OptiGen prcd-PRA test: |
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| Parent 1 Status | Parent 2 Status | ||
| Clear | Carrier | Affected | |
| Normal/Clear | All = Normal/Clear | 1/2 = Normal/Clear 1/2 = Carrier |
All = Carrier |
| Carrier | 1/2 = Normal/Clear 1/2 = Carrier |
1/4 = Normal/Clear 1/2 = Carrier 1/4 = Affected |
1/2 = Normal/Clear 1/2 = Affected |
| Affected | All = Carrier | 1/2 = Carrier 1/2 = Affected |
All = Affected |
For an explanation of Autosomal inheritance visit this page.
Please note, the above expected results are based on Mendelian inheritance and the percentages are based on probability, unless the same two parents produce 100 offspring together (probably impossible!!) the difference between expected outcomes and actual results can vary hugely due to the small sample size i.e. a litter containing 6 pups as opposed to 100 puppies!
If you mate a "clear" to a "carrier" the expected ratio of "clear" to "carrier" offspring is 50/50, however it is possible that the entire litter could be "carrier's"! Mate the same parents again and the next litter could be 25% "clear" and 75% "carriers", mate the parents again and the entire litter could be "clear"! The inheritance of genes is a random process and in a small litter all could be "carriers" or all could be "clear" (when mating "clear" to "carrier").
prcd-PRA is inherited as a recessive trait. This means a disease gene must be inherited from each parent in order to cause disease in an offspring. A carrier has one disease gene and one normal gene, and is termed “heterozygous” for the disease. A normal dog has no disease gene and is termed “homozygous normal” – both copies of the gene are the same, a dog with two disease genes is termed “homozygous affected” – both copies of the gene are abnormal.
Although prcd-PRA is inherited, it can be avoided in future generations by testing dogs before breeding. Identification of dogs that do not carry disease genes is the key. These "clear" dogs can be bred to any mate - even to a prcd-affected dog which may be a desirable breeding prospect for other reasons.
Normal/Clear (A1) dogs, meaning statistically normal for prcd-PRA will never develop this disease or pass it to any offspring. To date, no known normal/clear (A1) dog has developed prcd-PRA or produced prcd-PRA-affected offspring. (Source OptiGen)
Normal/Clear A/A1 can be bred to any dog
Carrier B/B1 should be bred only to A/A1 (Normal/Carrier)
Affected C/C1 should be bred only to A/A1 (Normal/Carrier)
The test makes it possible to breed from Carriers (B/B1 to B/B1) as long you test any puppies before breeding from them. Don't be afraid of your Carriers (B1´s), they ARE sound and will NEVER develop prcd-PRA - breed on with them in a controlled way i.e. ensure you mate them to a Normal/Clear (A1) partner and then test any pups who will be subsequently bred from.
To see Powerscourt prcd-PRA test results please visit our health testing page.