Genetic disorder testing should always be considered only one part of the determination of genetic merit and mate selection of a dog prior to breeding. It should stand alongside, not take the place of, other screening tools such as veterinary examination, behavior assessments, echocardiograms, ophthalmic exams, hip or elbow dysplasia screening, or performance tests. Some breeds have many known genetic disorder tests available that are applicable to them, and others have very few, either because they do not suffer from a high incidence of genetic disease, or because their disorders have not been researched or are complex in nature. Some disorders are associated with development of disease in all breeds, and others are only significant in single breeds. Wisdom provides as much information as is currently known about the significance of a disorder in a given breed and will update the information provided in our reports if new research alters current understanding. The process of research and discovery is ongoing, which benefits the breeder in their pursuit of improvements in health, performance, and beauty in each generation, but does demand an attitude of learning to be successful.
It is also very important to understand that genetic disease is common in all mammals, including dogs and humans, regardless of the quality of the breeding. Based on the 1000 Genome Project, humans are known to carry 50-100 known genetic disorder variants on average, and another 250-300 variants that hamper optimum function. The concept of all organisms carrying genetic disorder or loss-of-function variants is called genetic load. Dogs are thought to carry similar genetic loads to humans. In fact, in Wisdom’s most recent study of 1 million dogs, including both purebred and mixed-breed dogs, we found that 57% of dogs carry at least one known genetic disease variant.
Genetic disorder variant testing is now understood to be less about extinction of genetic disease and more about management and wise pairing of dogs. Genetic disease in dogs is not rare, it is normal. Loss of health is only noted when disease variants are inherited in the right combination to produce visible disease. The idea of inbreeding to discover and purge dog lines of genetic disease until they are “clean” is a myth. Instead, we now know that the greater the genetic diversity, the lower the likelihood that two or more matching risk variants will be inherited to produce disease, and the more options there are to breed away from something undesirable if discovered. Allelic frequency tells us how often a variant or allele is found within a population (e.g., a breed). Since each individual carries two alleles (one from each parent) for most genes, everyone contributes two copies to the total for the population. For example, if 1 out of 10 dogs carries a single copy of a given allele, then the frequency is 1/20, or 5% allelic frequency. Carriers and at-risk dogs for genetic disease should be considered in a holistic manner, which we will discuss below.
The term “carrier” in the context of genetic type, or genotype, refers to a dog that has inherited one copy of a recessive trait or disorder variant. It is common for a breeder to be concerned when they discover their tested dog is a carrier for a genetic disease, and they may wonder if the dog is the product of “bad breeding” or a bad line. This is often not the case. It is important to remember that if the dog is a carrier for a recessive disorder, they are not at risk of development of the disease themselves, but they can pass the variant to their puppies if bred. The first goal is always to ensure the health of the planned puppies, and then to select for the long-term goals you have for your breeding program. Many breeders hope for simplicity in their breeding or are afraid of ridicule, and the first reaction is usually the impulse to quietly discard the dog for breeding purposes. However, as discussed, genetic disease in dogs is commonplace, so a better approach is to ask the following questions:
Asking these questions will give you a much better idea of what the variant means for your dog and your breeding program. If the disorder is present in 30, 50, or even 90 percent of your breed, discarding carriers would severely damage your breed’s gene pool in a very short time if collectively all your fellow breeders discard their carrier dogs. Variants which occur as two copies in almost all dogs are said to be “fixed” in the breed and will be nearly impossible to safely avoid for many, many generations. Although you have likely done a great deal of research and careful consideration, your breed is not just your kennel, but a population of dogs, kennels, and breeders, so their behavior will affect your decisions and options as well.
With high carrier rates, disorders must be managed in the population over time, not eradicated immediately. If the disease is quite mild, such as ichthyosis which causes mildly scaly skin, the urgency of corrective action is reduced. Genetic testing is only one measure of a dog’s merit, so consider the other factors as well. Do they have an excellent temperament? Great structure? A solid pedigree? If the dog is a carrier for a disorder, but otherwise an excellent specimen, you may safely breed to a complimentary clear dog, and perhaps choose a replacement dog of the same sex that tests clear to carry on your breeding program. Lastly, if your breed is endangered, you must be especially careful to slowly reduce genetic disease frequency, so you don’t jeopardize the genetic diversity of the breed, which itself is a protection against disease.
The term “at risk” or “affected” in the context of genetic type, or genotype, refers to a dog that has inherited one copy of a dominant trait or disorder variant, or two copies of a recessive trait or disorder variant. Much like in the case of carrier dogs, a breeder may wonder if the dog is the product of “bad breeding” or a bad line. In reality, the main distinction between at-risk dogs and carriers is that this dog may produce at-risk or affected offspring if a dominant disorder, or all carrier puppies if they are at-risk/affected for a recessive disorder. However, if when considering the dog, you determine that the benefits outweigh the risks and the resulting puppies would not be at risk, you may still responsibly choose to breed him or her to a dog that is clear for that disorder. If you have many other dogs available to you that are of equivalent merit and clear or carriers, perhaps you will choose to use them instead, and retire that dog. Again, with rare breeds or those with small gene pools, you must be careful to maintain genetic diversity of the breed, which is also a protection against disease. Loss of genetic diversity is much more difficult to manage than a single disorder, so it is best to keep your breed’s legacy in mind.
Genetic testing should never be considered the only measure of a dog’s merit to a breeding program. It should be viewed as one of many screening tools, and always seasoned with a breeder’s good sense of holistic goals for their kennel. Each breeder will have slightly different sensibilities about what they prefer in their dogs, which in an ideal world will encourage the preservation of the full variety of the breed to be enjoyed for generations to come. Some breeds are managed from within western registries, others are working landraces used for particular purposes in a specific region. The process of research and discovery is ongoing, and Wisdom Panel™ is honored to partner with breeders around the world in delivering the latest in genetic science in service of the preservation and enjoyment of our dogs, now and in the future.
