P.R.A. Testing - a Genetic Breakthrough for the Cardigan Welsh Corgi
By Helen Arps, Auckland
It's not often that a minority breed can lead the way in the dog world, but the Cardigan Welsh Corgi is one breed that has helped science crack the genetic codes for the transmission of a disorder that has vexed breeders for decades.
So how was this done ?
Before we look at the achievements, we must first look at the history, for it is from history we learn.
P.R.A. was first discovered in the Cardigan breed in the 1960's. Several cases found in close proximity in Sydney Australia which launched a detailed examination of pedigrees, led to the discovery that this eye disorder was indeed an inherited problem in the Cardigan.
As is common this type of discovery, accusations, recriminations ultimately leads to a loss of many breeders and with it many lines. The Cardigan was not immune to this, but what also resulted was a banding together of breed enthusiasts who made strenuous efforts to eradicate it.
P.R.A. is a genetic defect that effects the retina of the eye causing general retinal degeneration, eventually leaving an affected dog blind. In Cardigans this condition is inherited recessively, that is for a dog to be affected BOTH parents must be carriers. Affected dogs will show sight deterioration, first noted by night blindness, usually by the age of 12 months. This will eventually lead to complete sight loss in many.
Following the attempts of early breeders to eliminate the problem using careful breeding programmes, the reported cases of affected Cardis reduced to nil and it was thought by many that this problem was beaten. Unfortunately, as with all genetic disorders, it is impossible to know what percentage of the breeding population are carriers and by the late 1980's and 90's breeders in Holland and the USA were again reporting cases of P.R.A. affected Cardis to the breed clubs. Here in New Zealand new cases were also reported.
It was with great excitement that in the late 90's it was learned that a project already was underway at the Centre for Veterinary Science at the University of Cambridge. Veterinary scientists, Dr David Sargan and Dr Simon Peterson-Jones, funded by the Wellcome Trust, had been working on and discovered a test for the same condition in the Irish Setter. It was due to the efforts of the Cardigan Welsh Corgi Association in the UK, that the Cardigan was accepted as their next project breed.
Once again the cooperation of breeders was to the forefront. Despite the devastation of discovering that some of the top Cardigans carried this gene mutation, breeders selflessly submitted blood samples from suspected families to advance the work of the scientists. This cooperation quickly led to the discovery of the mutant gene and a test was finally announced in April 1998.
The test detects the mutation on the affected gene. Results are either:
a) Normal - the dog has 2 copies of the normal gene and therefore cannot pass on the disease.
b) Carrier - the dog has 1 copy of the normal gene and 1 copy of the mutant gene. This dog will not develop the disease, but will pass the mutation on to it's progeny, if mated to a normal dog or produce affected progeny if mated to another Carrier.
c) Affected - the dog has 2 copies of the mutant gene and will develop P.R.A., usually by 12 months of age
The Cardigan breed suffers from very few known genetic disorders - P.R.A. is the only one documented. Breeders now have the tool to eliminate this disorder, and many have taken the opportunity to have their dogs tested. Registers of test results are held by breed clubs throughout the world, and anyone contemplating purchasing a Cardigan should check that the sire and dam have either been tested or all direct ancestors have been tested and certified as normal.
The test announced in April 1998 was a blood test and necessitated the drawing and sending of samples to laboratories in the UK or the USA. Thankfully science has again progressed and now test kits for oral mucosal tests are available. These are both accurate and substantially less costly than the blood tests.
Cardigan breeders have much to be grateful for. We have been given the tool to eliminate a devastating disease. Within one or two generations we should be able to eliminate P.R.A. from our breed, thanks to the amazing advances of science and the dedication of our breeders throughout the world. We hope that the benefits we now enjoy will be passed on to other breeds.
Published in N.Z. Kennel Gazette, February 2001, Supplement and reproduced with the kind permission by the author.