Genetic testing: An expanding frontier

When I was working in clinical practice full time, my experience with genetic testing looked something like this: a client would come in with a Dobie or an Aussie for a wellness exam, and as part of my client education, I would recommend they consider testing for vonWillebrand’s Disease (vWD) or multi-drug resistance (MDR1), respectively. I would explain the reasons for my recommendations, the risks associated with each condition, and the benefits of knowing if their pet had the condition in question. Often, despite my best efforts, the client would decline to pursue the test, and I would document it in the medical record.   

In other cases, a client would come in with their mixed-breed dog and ask me what mix of breeds I thought their dog was or even ask about genetic testing to determine their dog’s breed makeup.  I would reply that they could pursue genetic testing on their own if they wanted this information, mainly for their own curiosity. That was often the limit of my experience with and exposure to genetic testing. 

Undoubtedly other veterinary professionals have been making better use of the available genetic testing options for their patients. But in this area of rapid technological advancement, it can be hard to stay abreast of all the types of genetic testing available, along with the benefits and pitfalls of these tests.  

To learn more, I asked two experts in the field of genetic testing to decode genetic testing in veterinary medicine: how it’s being used, the benefits to pet owners and veterinary professionals, and some trends to watch as genetic testing becomes more widely utilized.  

Types of tests 

Genetic tests can be classified in a variety of different ways: by the number of genetic traits tested for, the type of information given by the test result, the way in which the test determines the result, and the avenue via which the test is made available. 

Many veterinary professionals are familiar with single gene tests for mutations such as MDR1 and vWD that have been available for years. The results of these tests can help veterinarians make decisions about drug utilization and safe surgical interventions and also counsel pet owners on ways to avoid complications in affected dogs.  

In addition to tests for specific genetic mutations, tests now exist that can determine a pet’s breed makeup, ancestry, and even inbreeding coefficient. According to Adam Boyko, PhD, Associate Professor of Biomedical Sciences at Cornell University, newer tests are emerging that can determine a dog’s age or screen dogs diagnosed with cancer to determine which treatments might be most effective. 

Testing methods vary as well. According to Liza Gershony, DVM, PhD, Geneticist and Outreach Coordinator at the UC Davis Veterinary Genetics Laboratory, genetic tests are often classified as direct or indirect.  Direct tests look for the genetic variants that are known to code for a specific trait or condition. Indirect tests, on the other hand, look for markers that are near the gene in question that can provide clues as to whether a mutation is present or not. Gershony added that direct tests are more accurate and should be preferred whenever possible.  

Test classifications

Genetic tests can also be classified based on whether they are marketed directly to pet owners versus being ordered or conducted by a veterinarian. With the convenience of cheek swab sampling, pet owners can purchase their own kit to collect a DNA sample and send it to one of several companies that provides an array of genetic testing information directly to the consumer without any veterinary intervention (that is, until the pet owner brings their report to their veterinarian for help interpreting it). Other tests are run through genetics laboratories often associated with veterinary schools and typically require an order and sample preparation by a veterinarian (although some labs of this type market directly to consumers as well). 

Prediction of disease 

“The biggest benefit of doing genetic screening early is the ability to use that knowledge to prevent disease later on,” Boyko said. This can include conditions such as urate bladder stones that might be prevented with a therapeutic diet or MDR1 mutations that benefit from avoiding the use of certain drugs.  

Other benefits include knowing what signs to watch for in order to seek treatment earlier or what precautions to consider in the case of future complications (e.g. a pet with a bleeding disorder who may need a blood transfusion more quickly in the case of an injury). “Even for conditions like degenerative myelopathy where there is no cure,” Boyko added, “knowing your dog is at risk allows you to keep a close eye and notice when symptoms develop (dogs are experts at masking symptoms) so that you can keep your dog as comfortable as possible and possibly avoid unnecessary, expensive diagnostic testing.”  

Boyko pointed out that in some breeds, knowing about certain genetic mutations can help owners better tailor their preventive care plan for their pets. Labrador retrievers, for example, can be predisposed to overeating and obesity if they inherit a mutation in their pro-opiomelanocortin (POMC) gene.   

Responsible breeding 

According to Gershony, “When deciding whether to breed an animal, knowing whether that animal is affected, at risk, or a carrier of a genetic condition provides valuable insight and allows breeders to make informed decisions in selecting breeding pairs that will not produce affected offspring.” For this type of screening to be helpful, it’s important to know which genetic mutations to test for. Many conditions are breed-specific, Gershony explained.  

She highlighted polycystic kidney disease (PKD) in Persian cats as an example of the positive effects proactive genetic testing can have on reducing the incidence of a condition within a breed, saying the frequency of the mutation for PKD has been “significantly reduced” since genetic testing for it came on the market. 

Coat color genetics is another area of interest for breeders. “Genetic testing allows breeders to predict possible coat color combinations for the offspring of a specific mating pair,” Gershony said, adding that such testing can help them create more puppies or kittens in highly sought-after colors and choose which of their animals to include in their breeding program. While this may seem to serve purely cosmetic purposes, that is not the case. The Merle allele, for example, is linked to both coat color patterns and certain otic and ocular abnormalities when two copies are present in offspring. Genetic testing can help breeders avoid this outcome. 

Effects on pet insurance 

Since pet insurance companies typically exclude pre-existing conditions from coverage, what will happen if an owner finds out which conditions their pet is genetically at higher risk for? Can these conditions be excluded from coverage as well even if before the pet has been diagnosed with anything?  

“Pet insurance companies already use genetic information to make pricing and exclusion decisions, they just do it based on knowing what the breed the dog is,” Boyko said. As of yet, he added, pet insurance companies don’t seem to be using genetic test results from specific pets to determine their insurability, but who knows if or when that will change? 

Even if pet owners don’t identify markers for disease through genetic testing, determining the breed makeup of mixed breed dogs may give pet insurance companies information to guide their risk analysis and premium pricing in new ways (which could be beneficial or detrimental to pet owners depending on the results).  

There are some instances in which having genetic test results could work in favor of greater coverage for a pet, Boyko said. He gave the example of a pet whose breed is known to have a high propensity for certain genetic conditions. If this pet undergoes genetic testing, however, and is determined to not carry a particular mutation or otherwise not be at high risk for developing the condition, they might qualify for more complete coverage and/or lower premiums for coverage than they might have otherwise just based on their breed.  

The risks of knowing 

Apart from the concern over insurability, there can be other risks to knowing a pet’s genetic makeup and predisposition for disease states. For starters, there’s the anxiety that can come with the anticipation of disease that may never develop since having a positive result for a particular genetic marker is not always a guarantee of future disease. Degenerative myelopathy (DM) is one such example. Dogs can test positive for two copies of the genetic mutation for this incurable disease, which can lead to consternation on the part of veterinary teams and pet owners when in some cases the dog will never show signs of the disease. 

In other cases, finding a single genetic mutation is not sufficient to determine if a pet will develop the condition in question. “Many diseases have more than one genetic cause,” Gershony explained, adding that there are more than 20 mutations associated with progressive retinal atrophy in dogs. Identifying one or more of these mutations on a genetic test will by no means determine that a dog will develop the condition. By the same token, testing negative for the known mutations associated with PRA could give pet owners a false sense of security that the condition will not develop in their pet. 

Likewise, some breeds of dog do not appear to be at risk for developing certain disease states. So, a positive result for a genetic mutation may be meaningless for some breeds. Getting positive results without having a clear understanding of their significance can result in undue anxiety and in some cases unnecessary testing or treatment.  

Looking to the future 

Both Boyko and Geshony agree that the availability of genetic testing will likely continue to grow over the coming years. “Technology for genetic and genomic research has advanced considerably in the past decade,” Gershony explained, “and the increase in available resources allows for further discoveries of genetic causes behind diseases and other physical or performance traits.” 

Boyko is excited about the potential for behavioral genetics to make predictions about temperament and trainability, particularly when it comes to selecting and training working dogs.  

For veterinary professionals who aren’t all that comfortable with genetic testing yet, Gershony recommends that they take time to learn what is now available. This will help them be more prepared when clients come asking questions about testing (or when they come with test results for you to interpret).  

Boyko added that even without any fancy testing, veterinary professionals are already performing genetic testing by proxy by evaluating your patients’ risks for certain conditions based on factors like breed. New genetic testing options allow veterinary teams to “go one layer deeper” and provide “personalized” information for clients about their pets.  

As both technology and our understanding of animal diseases continue to progress, and as pet owners continue to ask for more advanced preventive and treatment options for their pets, it is very likely that genetic testing will occupy a more central role in veterinary medicine. Staying informed of the latest developments in this evolving field will help veterinary professionals make the most of what genetic testing has to offer. 

Photo credit: Nikos Papanikolakis/iStock via Getty Images 

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