Until recently extensive pedigree analysis and complex test mating programmes have been the only way to detect animals carrying genes for inherited disease.

The genes responsible for inherited disease are embedded in the amazingly complex DNA molecule which is the genetic blueprint for every individual. Over the last five to ten years scientists have begun to identify individual genes and DNA-based technology has been developed to test animals for the presence of disease-causing genes. At the moment there are only a few tests available, but tests for many more of the common inherited disorders will become available in the future.

Once tests become widely available for specific disease genes, breeders will be able to pre-screen stud dogs or bitches to ascertain carrier status. If a new carrier is identified potential mates can also be screened and matings between two carriers avoided. By tracking disease genes in this way the gene will be diluted in the next generation and ultimately be eradicated.
 
 

The Kennel Club’s canine genetics co-ordinator

The Kennel Club has established the post of Canine Genetics Co-ordinator and the first appointee is Dr Jeff Sampson, from the Centre for Preventive Medicine at the Animal Health Trust.

He writes: "My initial task will be to ensure that the potential offered by this new technology becomes widely understood by all those involved with dogs. In the first instance, the role is one of education: assimilating, interpreting and communicating the new scientific information to dog owners and breeds, Breed Clubs and Councils, those involved in veterinary care, post-graduate and  undergraduate veterinary students and of course the Kennel Club. An important aspect of my post will be to liaise with research groups the world over so that I can quickly pass new and exciting discoveries ‘down the line’. I hope also to work with breeders and Breed Clubs so that we can identify and prioritise the genetic problems that breeders are most worried about. I will also to explore new areas of funding and see to develop significant resource for basic and applied health programmes that will improve the genetic health of our dogs. I think that specialist centres will need to be developed where sophisticated genetic testing can be carried out and where scientists can help and advise breeders on how to evaluate the results of individual tests and plan mating programmes. I see the partnership between scientists, breeders and Breed Clubs and The Kennel Club as being crucial if we are to begin to eradicate these genes from the general canine population."
 
 

Genetic screening tests
 
 

        Do dogs have inherited diseases?
Over 350 inherited diseases have been recognised in dogs. Many are restricted to particular breeds but others such as hip dysplasia occur in a wide range of breeds. The different diseases affect almost every part of the dog’s body including eyes, heart, skeleton, liver and skin.

        Are these diseases common?
Most inherited diseases are rare and only seen in restricted pedigrees within particular breeds. However, several diseases are common such as deafness in Dalmations, where about 5% of dogs are deaf in both ears and 13% are deaf in one ear.

        Why do dogs have these problems?
Many of the diseases in dogs are inherited in ‘recessive’ manner (ie a faulty copy of the gene is inherited from both the father and mother). Populations which show high levels of recessive disorders are usually inbred.
        Many pedigree breeds were founded with a very few individuals which were closely interbred. This has led to the prevalence of ‘faulty’ genes in some breeds and the appearance of inherited diseases.

        Is there a cure for these diseases?
There is no cure for most of the diseases although in several cases it is possible to treat the symptoms of the disease.

        Are there schemes for testing for inherited diseases?
Yes there are schemes run jointly by the Kennel Club and the British Veterinary Association to evaluate dogs for eye disease and hip problems.
        These schemes have played a valuable role in reducing the incidence of genetic problems in dogs for these conditions.

        How do genetic screening tests help?
Tests can determine whether or not a dog has an inherited disease. However, dogs which do not have the  disease may be carriers (carry a copy of the defective gene). If a carrier is bred with another carrier it is likely that approximately 25% of their offspring will be affected with the disease. Thus the carriers act as a silent reservoir for the disease. In contrast, genetic screening can identify carriers and it can identify dogs which are likely to develop the disease later in life.
        If only dogs which are not carriers are used in breeding programmes, the defective gene will not be passed onto successive generations and the disease will disappear.

        Which diseases can be tested for?
The Animal Health Trust offers a screening test for progressive retinal atrophy in Irish Setters and copper toxicosis in Bedlington Terriers. Tests are being evaluated for fucosidosis in English Springer Spaniels, globoid cell leukodystrophy in West Highland White and Cairn Terriers, phosphofructokinase deficiency in American Cocker Spaniels, pyruvate kinase deficiency in Basenji and von Willebrands disease in Scottish Terriers.

        What do I do if I want to get my dogs tested?
Ask the Trust for a DNA testing form which details the procedure. You will need to discuss your wishes with your vet, who can who will send us a small blood sample from your dog. We will isolate DNA and carry out the genetic test. The result will usually be sent to your vet within four weeks.

        Are there other DNA tests?
We offer DNA-based parentage testing which can be used to determine parentage, eg if a bitch may have been mated by more than one dog, or if the pups of a litter do not have the expected characteristics.