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prcd-PRA in Golden Retrievers

8/14/08

The response by golden retriever owners and breeders to the knowledge that prcd-PRA occurs in their breed has been exemplary of what any conscientious breed club would hope for.  Since it became known that prcd-PRA was the cause of a clinical case of PRA in a golden retriever that had been examined by veterinary ophthalomologist, Dr. Gus Aguirre, in 2007, the golden retriever community has been actively getting the word out that this disease is one to be considered in the overall health assessment of their dogs.  To date, OptiGen has tested hundreds of golden retrievers from multiple lines and countries for prcd-PRA and so we can now provide more extensive information on the incidence of the disease in this breed. 

For those who are not familiar with prcd-PRA, please read about prcd.   prcd-PRA is the most common type of PRA and is found in over 20 breeds of dog.  In every year since the mutation’s discovery, new breeds have been identified in which the same prcd mutation is shown to be associated with PRA.  This leads one to conclude that prcd-PRA must be quite an old mutation and that it likely arose in the dog population before many of the breeds were segregated into distinct “closed” breeding structures.  In all breeds where prcd-PRA is identified, a similar clinical presentation is seen.  prcd-PRA affected dogs initially lose night vision. This is followed by a gradual loss of vision in bright light and then, over enough time, complete blindness is likely. As with most diseases, some variation in symptoms can be expected, however in most breeds clinical prcd-PRA disease can be observed during a veterinary ophthalmology exam in genetically affected dogs by the time they are 4-6 years of age.  There are a couple of breeds, the English Cocker Spaniel and the American Eskimo dog, where much later onset of clinical symptoms is not uncommon. Occasionally individuals in other breeds also show this late-onset variation, although this is rare.  The cause of this variation is of particular interest to vision researchers and is an active area of study in associated academic laboratories. 

The course of prcd-PRA disease in the golden retriever is based on a limited number of clinical cases however we have no reason to expect a different pattern than what is observed in most other breeds—i.e. that clinical symptoms are likely to be apparent to veterinary ophthalmologists by the time the dogs are 4-6 years of age.  This has been true for the two prcd-PRA affected golden retrievers that we have received at OptiGen that are of diagnostic age.  We have also found a few other golden retrievers to be genetically affected through OptiGen testing, however all of these dogs are still less than 3 years old and therefore below an age where clinical diagnosis is likely to be observed. We ask anyone with PRA affected dogs to please keep OptiGen updated with any changing information on their dogs’ eye examinations so that we may add to the understanding of this disease in all breeds.

As of mid-summer 2008, based on the tests we’ve completed at OptiGen, here is a summary of we know about PRA in the golden retriever:

  • 1%  are (genetically) AFFECTED with prcd-PRA
  • 26% are CARRIERS of prcd-PRA
  • 73% are NORMAL for prcd-PRA
  • All of the prcd- AFFECTED (genetically) dogs are from either the USA or Canada
  • 82% of the CARRIERS are from the USA & Canada. The remaining 18% are from multiple countries in Europe and the UK

It should be kept in mind while interpreting these statistics that, although hundreds of Goldens have been tested, there is still a sample bias that is likely influencing the data.  When an AFFECTED or a CARRIER is identified, conscientious owners make sure that others who have close relatives of that dog are notified.  This in turn leads to the testing of Goldens with a higher chance of carrying the prcd mutation than would be expected in the general population.  So the 26% carrier rate does not reflect the chance of any golden retriever carrying the mutation and the 1% Affected rate we’ve observed is very likely higher than what would be expected in the general population of Goldens.  The CERF statistics for years 2000-2005 show that 0.05% of the Goldens examined had clinical PRA and this is likely a more accurate expectation of prcd’s incidence in the general Golden population.  It should also be noted that some of the Carriers that were tested at OptiGen are sires that have been prolific breeders.  Fortunately the majority of their mates were Normal for prcd and so relatively few Affected offspring have been produced.  It is particularly good luck that the DNA test is available at this point –to check the spread of prcd in Goldens, particularly in these lines.

It is important for Golden breeders, particularly those in Europe, to be aware that there is at least one other form of PRA that occurs in the breed. Unfortunately there is no DNA test available for the other form(s) yet.  We have received a few samples (less than 10) from purebred Goldens in Europe where PRA has been diagnosed however test results show that these dogs are Normal for prcd-PRA.  Similarly, a non-prcd PRA-affected golden from Canada was received at OptiGen.  At this point, it appears that the major form of PRA in North American Goldens is prcd-PRA and that another, molecularly unidentified, form of PRA is more prevalent in Europe. OptiGen offers free PRA testing for pedigreed dogs that have been diagnosed with PRA by a veterinary ophthalmologist.  For more information on this program see our Research page.

An article on PRA in the Golden Retriever, written by Dr. Ann Hubbs, chairperson of the Health and Genetics committee for the Golden Retriever Club of America, will appear in the early Fall issue of Golden Retriever News and will also then be viewable on the GRCA website.   


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Tel: 607 257 0301 · Fax: 607 257 0353 · email: genetest@optigen.com or optigen@clarityconnect.com
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