What is RCD4 Progressive Retinal Atrophy (PRA)?
Progressive Retinal Atrophy (PRA) is a well-recognized inherited condition to which many breeds of dogs are predisposed. The condition is characterized by bilateral degeneration of the retina which causes progressive vision loss that culminates in total blindness. There is no treatment for PRA, of which several genetically distinct forms are recognized, each caused by a different mutation in a specific gene. The various forms of PRA are typically breed-specific, with clinically affected dogs of the same breed usually sharing an identical mutation. Clinically affected dogs of different breeds, however, usually have different mutations, although PRA-mutations can be shared by several breeds.
Geneticists at the Animal Health Trust (AHT) have identified a recessive mutation that is associated with the development of PRA in the Gordon Setter. The research has revealed that there are at least two forms of PRA segregating in the Gordon Setter. The DNA test we are offering is for the mutation that causes one of these forms, rcd4; the mutation that causes the additional form has yet to be identified.
Rcd4 is the most common form of PRA among Gordon Setters and the development of this test therefore enables breeders to slowly decrease the frequency of an important form of PRA in their lines. However, because we know that at least one other form of PRA exists within the breed, we cannot guarantee that any dog will not develop PRA, even if they are clear of the rcd4 mutation.
Research has demonstrated that the frequency of the rcd4 mutation in Gordon Setters is high and as many as 50% of dogs might be carriers. The mutation is recessive which means that all dogs can be bred safely but carriers and genetically affected dogs should only be bred to DNA tested clear dogs. About half the puppies from any litter that has a carrier parent will themselves be carriers and any dogs from such litters that will be used for breeding should themselves be DNA tested prior to breeding so appropriate mates can be selected.
It is advisable for all breeding dogs to have their eyes clinically examined by a veterinary ophthalmologist prior to breeding and throughout their lives so that any cases of PRA caused by additional mutations can be detected and that newly emerging conditions can be identified.
Information supplied by the Animal Health Trust, used by permission.
The RCD4 PRA DNA test can be ordered for the following breeds:
Australian Cattle Dog
Irish Red & White Setter
Polish Lowland Sheepdog
Normal – These dogs have two normal copies of the gene. Clear dogs will not develop Progressive Retinal Atrophy as a result of the rcd4 mutation, although we cannot exclude the possibility they might develop PRA due to other mutations they might carry that are not detected by this test.
Carrier – These dogs have one copy of the mutation and one normal copy of the gene. These dogs will not develop PRA themselves as a result of the rcd4 mutation but they will pass the mutation on to approximately 50% of their offspring. We cannot exclude the possibility that carriers might develop PRA due to other mutations they might carry that are not detected by this test.
Genetically Affected – These dogs have two copies of the rcd4 mutation and will almost certainly develop Progressive Retinal Atrophy during their lifetime. The average age of diagnosis for dogs with the rcd4 form of PRA is 10 years of age, although there is considerable variation within breeds.
The Rcd4 mutation responsible for late-onset Progressive Retinal Atrophy was discovered by researchers at the Animal Health Trust (AHT) in the UK studying Gordon Setters. Their research found that dogs with 2 copies of this mutation have a high incidence of loss of vision due to this form of Progressive Retinal Atrophy at around 10 years of age. This has been demonstrated in Gordon & Irish Setters. The mutation was also seen in English Setters by screening random samples of DNA banked for other purposes. This mutation has not yet been seen in Irish Red & White Setters, but since they share the prcd1 form of PRA with Irish Setters, it is reasonable to suspect that they may have this form of PRA as well.
Random screening of other breeds by the University of Missouri research team found that this mutation is also present in Australian Cattle Dogs, Polish Lowland Sheepdogs, Small Munsterlanders, and Tibetan Terriers. A study of Tibetan Terriers with PRA showed that this mutation is responsible for one form of late-onset PRA in this breed as well, with age of onset similar to the Gordon & Irish Setters in the original research. As with Irish Setters, there is more than one form of PRA present in the Tibetan Terriers studied, and the mutations responsible for these other forms of PRA are as yet undiscovered In Tibetan Terriers.
Owners of dogs from these breeds who want to avoid the risk of producing this late-onset form of PRA can use this DNA test to screen their dogs and make appropriate breeding choices.
Thanks to an agreement with the AHT, testing for this mutation has been made available to residents of North America and others through the OFA/University of Missouri DNA testing partnership. Orders are placed through the OFA Website, DNA samples will be collected via FTA cards sent in a kit following the order, the Small Animal Molecular Genetics Lab at the University of Missouri will run the test, and the OFA will report the results. Inclusion of the results in the OFA database is included with the order.
Tests are ordered online through the secure area of the OFA website. Payment is accepted by credit card (MasterCard and VISA). The OFA administers all order handling. Upon receipt of an order, the OFA will send out the test kit which will include a Foam-Tipped Applicator card for DNA sample collection, along with sample collection instructions. Using the FTA card technology, owners can safely collect DNA samples at home. The collection process is non-invasive, and no veterinary appointment is necessary.
Samples are then sent to the University of Missouri College of Veterinary Medicine where the samples will be processed by the Small Animal Molecular Genetics Lab. Results will be forwarded to the OFA, and the OFA will issue the resulting report to the owner.
The fee for each test includes the test kit, laboratory processing, and subsequent registration in the OFA databases.