I've put in this page as there seems to be a lot of misinformation about the cord1 mutation. I've even seen puppies advertised as "free from the PRA virus". There are adverts for cord1 clear puppies suggesting that everything except clears are going to go blind. I've had a (non showing) stud owner inform me that two carriers cannot produce genetically affected puppies.
Progressive Retinal Atrophy is, as its name suggests, an advancing degeneration of the retina or parts of it. It is not a single condition but a description that covers a group of inherited disorders with this effect. In Dachshunds the cord1 mutation is inherited as a simple autosomal recessive. That is to say, the mutated gene is recessive to the unmutated gene, so a single copy of the gene will have no adverse effect on the individual.
The Animal Health Trust in Newmarket have isolated a gene mutation that causes a form of PRA in Miniature Long Haired Dachshunds from UK lines. This form of PRA is a degeneration of the cones and rods in the retina which results in gradual blindness. The researchers have named this gene Cord1 for Cone Rod Dystrophy 1.
The gene mutation has subsequently been found in Miniature Smooth Haired Dachshunds.
There is a non-invasive DNA test for both breeds. Swabs may be ordered from this email address swab.request@aht.org.uk.
Dogs can be quickly and permanently tested for this gene mutation by means of a simple cheek swab. This will give the dogs cord1 mutation status. It will tell you if the dog is clear of the mutation, is a carrier of the mutation or has two copies of the mutation.
Contrary to popular belief, a clear or carrier result does not mean a dog will never contract PRA, or that it is "PRA clear" as is often suggested. It simply means that the dog will not contract the form of PRA that is associated with the cord1 mutation. The term PRA describes a syndrome (a group of clinically recognisable symptoms) and there is more than one form of PRA.
Dachshunds are also susceptible to glaucoma and cataracts. We do not have a DNA test for these, but a BVA/ISDS/KC eye certificate shows the dogs status as regards those at the time of testing. I believe it is crucial for a stud dog to have this examination. We need to know why not all dogs with two copies of cord1 develop PRA, and we need to be alert for other forms of the condition. This is not possible without the manual exam. If problems are found, DNA can be submitted to the AHT for further analysis. This helps them and ultimately helps us breed healthier dogs.
"There may be other forms of PRA in the miniature dachshund population that are caused by a different mutation to cord1. The current DNA test is specific for the cord1 mutation and will not therefore detect dogs affected by alternative forms of PRA. During the course of our research we did see some evidence of another, late-onset form of the disease, in a restricted number of lines." Direct quote from http://www.aht.org.uk/genetics_dachpra.html
The BVA/KC/ISDS eye exam is being offered now at many Championship shows inexpensively, and at Crufts there are four whole days of free eye testing under this scheme laid on by the Kennel Club. Every entrant receives details of this and information on how to book a free exam. It is not painful and can be scheduled after the dog has been exhibited. Many ringcraft clubs and societies also offer this testing at discounted rates and eye clinics are held throughout the country. A look in the dog press will also yield details of testing sessions.
Cord1 is a mutation and so it makes sense to breed away from producing animals with two copies of the cord1 mutation. (genetically affected).
Percentages quoted below are chances PER PUPPY.
Clear to Clear will produce 100% clear puppies.
Clear to carrier will produce 50% chance of clear puppies, 50% chance of carriers. (Will need to test puppies wanted for breeding unless they are to be mated to a clear)
Clear to genetically "affected" will produce 100% carriers.
Carrier to carrier will produce 50% chance of carrier puppies, 25% chance of clear puppies and 25% chance of genetically affected puppies.
Carrier to genetically affected will produce 50% chance of carrier puppies and 50% chance of affected puppies.
There is no reason to remove carriers and genetically affecteds from the gene pool. Mated to clears they will not produce genetically affected puppies. We can immediately eliminate PRA caused by the cord1 mutation by not producing puppies with two copies of the gene. This way the mutation will be reduced or eradicated over time without damaging the gene pool.
"Because of the very high frequency of the cord1 mutation, we would advise breeders to take a gradual approach to eliminating the mutation from their stock to avoid restricting the gene pool available. Both carriers and affected dogs can be used to breed - but only when crossed with DNA tested clear dogs" Direct quote from http://www.aht.org.uk/genetics_dachpra.html
