Advances in DNA testing are identifying the genes behind some common conditions. This introduces the possibility of screening for these conditions and making appropriate decisions based on the screening results. It is important to understand what the results mean and what is an appropriate response.
Common conditions
Progressive Retinal Atrophy (PRA) refers to degenerative conditions that cause impaired vision and eventually blindness. Centronuclear Myopathy (CNM) presents from 2 to 5 months and severely inhibits muscle development. Both of these conditions are recessive, which allows the incidence of the condition in offspring to be predicted. Parents are categorised as affected when they have the condition, carrier when they are not affected but can pass on the condition, and clear when they are neither affected or a carrier. The incidence of the condition in offspring will, statistically, be as follows...
| Parents | Offspring | |||
|---|---|---|---|---|
| Parent 1 | Parent 2 | Clear | Carrier | Affected |
| Clear | Clear | 100% | 0% | 0% |
| Clear | Carrier | ~50% | ~50% | 0% |
| Clear | Affected | 0% | 100% | 0% |
| Carrier | Carrier | ~25% | ~50% | ~25% |
| Carrier | Affected | 0% | ~50% | ~50% |
| Affected | Affected | 0% | 0% | 100% |
What you should ask your breeder
It is important to recognise that being clear or a carrier are both clinically normal conditions. If you want a puppy and have no intention of breeding then a puppy that is either clear or a carrier will be equally acceptable. If you do intend to breed then you should still consider a puppy that is a carrier, but you will need to ensure that it's mating partner is clear.
Breeding to eliminate all affected and carrier dogs might at first seem attractive, but this might lead to dogs with otherwise excellent characteristics being ruled out unnecessarily. In addition, the narrowing of the gene pool that would result might throw up other conditions that are worse than those that are being targeted. Provided your prospective puppy is clear or a carrier then other characteristics such as temprament and build should take precedence. Obviously, an affected puppy should be avoided.
Testing for these conditions is not yet universal, and you may encounter breeders who do not test. Whilst their puppies may not be affected you cannot be sure unless you know the status of the parents or the puppies. If a breeder is unaware of the tests that are available, or tries to convince you that testing is not necessary, then you should carefully consider if they are the breeder for you. Any breeder asserting the testing status of parents or puppies should be able to back this up with certificates to prove the status. Copies of these should be provided with your puppy, along with its pedigree. The results of dogs tested for PRA can be found on the Kennel Club web site.