The study of genetic diseases in different breeds of dogs is very interesting, not just for veterinary medicine but also for human medicine.
The "Canine Genetics" team under the leadership of Dr Catherine André at the Rennes Institute of Genetics and Development has for more than ten years been conducting a number of research projects aimed at determining the molecular bases for genetic diseases in dogs. This research is targeting diseases whose clinical indications, genetic causes and therapeutic responses are shared by human beings and dogs. It thus provides a twofold benefit, for both dogs and human beings, improving diagnosis and screening through the introduction of genetic tests and the opening up opportunities of better therapeutic care.

More than 500 genetic diseases are listed for dogs. In many cases they are specific to certain breeds and their frequency can reach up to 20% within a given breed, posing real problems for the health and even the longevity of certain breeds.
The Rennes researchers have collected samples from infected dogs and healthy dogs of the same breed (the control cases) and their families as a way of researching the genetic causes of different diseases in different breeds. Since 2000, Cani-DNA - a bio-bank full of samples from dogs - has been developed at the CNRS in Rennes, following the establishment of a network of vets and breeders with the help of AFVAC and the French Kennel Club, the Société Centrale Canine. This network is basically made up of practicing vets, the four French schools of veterinary medicine, the company Antagène and various veterinary labs specialised in analyses and histopathology.
The genetic analyses carried out at the CNRS in Rennes start with taking blood samples from the infected dogs and their families. The DNA of each dog is then extracted and hundreds of thousands of genetic markers analysed for each canine DNA. This work ends with the production of a precise genetic map for each dog. The aim of the subsequent genetic and statistical analyses is to compare the genetic maps of infected dogs with those of healthy dogs, pinpointing the region of the genome possibly at the origin of the disease.

Here are a few examples of research in progress at the Rennes laboratory.

• The histiocytic sarcoma, a very aggressive tumour that spreads quickly to several organs, is particularly common in the Bernese Mountain Dog, the Flat Coated Retriever and the Rottweiler, while the disease is rare in other breeds. This type of cancer also exists in human beings, where it is very serious. Due to the fact that there are so few cases among human beings, there is hardly any genetic research done. No effective therapy currently exists, and evidently research into the canine form of the disease will benefit both dogs and human beings.
• The acral mutilation syndrome is found in breeds of hunting dogs, including the French Spaniel. This sensory neuropathy, probably due to innervation defects in a dog’s limbs, leads to limbs being mutilated. Mutilation can be very severe, and in the most serious cases, leads to the dog having to be put down. Several forms of sensory neuropathy exist in human beings, where they are classified as HSAN (Hereditary Sensory and Autonomous Neuropathy) disorders. Though genes have already been identified, they do not explain all forms; thus, finding new genes in dogs should help boost the number of genes involved in human beings.
• Retinopathy is characterised by a progressive sight disorder, usually ending in complete blindness. More than 100 breeds suffer from progressive retinal atrophy, including the Border Collie. Again, research into the genetic cause in the Border Collie is ongoing; studies already completed show a transmission linked to chromosome X. In humans, there are also many forms of this disease, which is called retinitis pigmentosa. Though its forms are related to chromosome X, its genetic causes are not yet known. To date, of the dozen known genes in the two species, the majority are the same.
• Hip dysplasia in large dogs is proving to be a major problem. A partially multigenetic component is thought to be the cause.

Finally, this type of study has recently allowed us to identify the defective gene responsible for ichthyosis in the Golden Retriever. This gene, also seen to be the cause of congenital ichthyosis in human beings, has allowed the discovery of a new function in the skin barrier. A genetic test has been developed for diagnosing and screening dogs, and is expected to allow better breeding management and a progressive decrease in the incidence of the disease in this breed.

Winding up, any dog lover, whether vet, breeder or simply a dog owner, may participate in these genetic studies, either by providing input to the Cani-DNA bio-bank (dogs of any breed and any age, healthy or sick), or for specific research projects. All you need to do is to send in a simple blood sample (3 ml in an EDTA tube), accompanied by a copy of the dog's pedigree and a filled-in clinical questionnaire provided by the CNRS.

Catherine André and Anne-Sophie Guillory

For more information: http://dogs.genouest.org
Contact : Catherine André
Tél. : 02 23 23 45 09
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