If we can't look to the molecular geneticists for solutions, then we must go back to basic principles of inheritance and the science of animal breeding for help. We know that osteosarcoma is highly heritable. In Scottish Deerhounds, the heritability of osteosarcoma is 0.7, which means that 70% of the variability in the occurrence of the cancer in Deerhounds can be attributed to genetics. The other 30% we attribute to "environment", our catch-all term for everything that is "not genetic". (If a trait has no genetic basis, heritability is 0%; if the trait is entirely determined by genes, then heritability is 100%.) The higher the heritability of a trait, the easier it is to change the frequency of the phenotype in the population by selection.
A heritability of 70% for osteosarcoma in Deerhounds means that a selection program can be very effective in reducing the incidence of the disease in the breed. And the most efficient way to run such a selection program is not by selecting against the phenotype directly, but by using information about the breeding value of each dog for the trait.
Heritabilities of Various Traits in Dogs
With no hope of a genetic test anytime soon for osteosarcoma in dogs, breeders should be able to significantly reduce the incidence of this cancer in their breed by using estimated breeding values. This requires only a pedigree database and the information about affected animals among a dog's relatives. A computer generates a number that reflects the "genetic value" of a dog for a particular trait, in this case osteosarcoma. By using this estimated breeding value (EBV) to identify dogs at lower risk for osteosarcoma, breeders can efficiently reduce the incidence of this cancer in the breed.
The real beauty of EBVs is that you don't need to know the genes involved in a trait or how it is inherited. You don't need to base selection decisions on a phenotype that might be only partially determined by genetics. The estimated breeding value is a numerical estimate of the what an animal will produce in its offspring.
EBVs can be used to improve selection against many genetic disorders. Heritability of other cancers are also relatively high: lymphoma in Golden Retrievers has a heritability of 44%, and histiocytosis in Bernese Mountain Dogs is 30%. Heritability of hypothyroidism in Beagles is 33%, mitral valve disease in Cavaliers is 33%, and epilepsy in Belgian Tervuren is 77%.
When a disorder pops up in a breed, breeders usually rush to identify the responsible gene so they can develop a test and select against. However, for many disorders a test is not likely to be forthcoming - not soon, and maybe not ever. Estimated breeding values offer a way to select against a problem much more efficiently than using phenotype alone, and all you need is a health database.
Several kennel clubs are already providing EBVs to breeders for hips (e.g., Finland and the UK), and these resources will continue to develop for other disorders. A website that will provide EBVs for hip and elbow dysplasia for dogs in the US based on the public data in the OFA database is in the works at Cornell, and ICB will be working with several groups of breeders in 2015 to get their data online and train them how to use it. For breeders that have been struggling to manage genetic disorders, sometimes for decades, we should be able to start seeing improvement soon if breeders will use it.The website is under development, but you can have a look here.
We will have an EBV course available online sometime in the next few months, but if there is a group in your breed that is interested in getting in on the initial stage of training and implementation of EBVs, please contact ICB and we can discuss what would be involved.
ICB's Population Genetics course lays the foundation for understanding how EBVs can be used as part of a strategy for managing genetic disorders in purebred dogs. The next class starts 5 January.
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You can learn more about the genetics of dogs in ICB's online courses.
*** Online course "Population Genetics for Dog Breeders" starts 5 January ***
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