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Cornell Richard P. Riney Canine Health Center

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Benefits of canine DNA testing

Learning about your dog’s genome can be fun and reveal valuable information about their health.

It can feel trendy to send a swab of your dog’s cheek cells to determine their background — the canine version of a genealogy test. But genetic testing can also give you vital information about your dog’s health. Additionally, your dog’s DNA sample may be used for research to study ways to advance the prevention, detection, progression and treatment of serious canine health conditions — helping future generations of dogs.

Genetics 101

Normally, dogs have 78 chromosomes. These are bands of genetic material (DNA) composed of nucleotides. There are four nucleotides: adenine, guanine, thymine and cytosine. How these are arranged and paired determines your dog’s genetic makeup. Each puppy receives half their genetic material from their dam and half from their sire.

For each gene, a dog has two copies, maternal and paternal. If the two copies match, it is considered “homozygous” for that gene. If they differ, then your dog is “heterozygous” for that gene.

Everyone loves a simple inheritance, where one gene controls a trait. In most cases, however, there are often all kinds of modifiers that influence whether a trait is expressed.

There are also “recessive” and “dominant” traits. For a recessive trait, your dog needs two copies (homozygous genes) for that trait to be expressed. If the trait is dominant, only one copy is needed (heterozygous genes).

And, finally, some traits are “sex-linked” and carried on either the X or the Y chromosome. Males have an X and a Y chromosome. Females have two X chromosomes. A male dog can get traits via the Y or via the X. A female will only show a trait if it comes on one or both of her X chromosomes.

If this information feels overwhelming, don’t get discouraged. The testing results are simpler.

Here’s the fun stuff

Doing genetic testing to breakdown the breed makeup of your dog can be fun, though we’re still in the early stages and some researchers question the accuracy.

Experts also emphasize that you shouldn’t feel doomed if your dog’s test reveals signs of hereditary diseases. For example, if your Golden Retriever’s genetic tests says they have a gene for muscle dystrophy, it doesn’t guarantee that they will get the disease. However, if your mix has the MDR1 gene, you will now know to notify your veterinarian and keep your dog away from certain drugs.

Remember, if the testing shows that your dog has a specific gene for any medical-related condition, discuss these results with your veterinarian before making any assumptions.

There are more than health issues involved though. Knowing your dog’s genetic background also may help predict some behaviors. For example, if your pup is 80% Border Collie, the odds are good that they will be very energetic, enjoy chasing things and show herding instincts.

Dr. Adam Boyko, associate professor in the Department of Biomedical Sciences and co-founder of Embark Veterinary Inc., had his own dog tested.

“My dog was a shelter mutt that I knew very little about, other than she was rescued from a hoarding situation. I was interested in not only knowing what she was possibly predisposed to in terms of health, but also anything about her background,” he said. “The shelter listed her as terrier-Basenji mix, which sounded a bit too exotic to be true.”

He continued, “For my dog, it really helped me get to know her so much better. She wasn’t at risk for any known genetic conditions, but she also wasn’t part Basenji and was another mix entirely.”

The ability to do DNA tests for dogs has much broader applications too.

“Breeders have long known the importance of genetic screening to avoid producing puppies affected with known genetic conditions, and newer tests looking genome-wide are also invaluable to help maintain diversity and minimize inbreeding in litters,” Boyko said. “For individuals with pedigreed dogs, genetic health screening is helpful to ensure you’ve added a healthy, well-bred dog to your home.”

Genetic testing can also be done to establish parentage. Some breeders will do a multi-sire litter, and each puppy will need to have their sire verified. Or there may be an “oops” where the breeder isn’t 100% certain which male bred the female. A simple swab can determine the paternity.

Health testing

But truly, the best use of genetic testing is for predicting and preventing canine health conditions.

Many diseases now have genetic markers that reveal if your dog will develop a genetic problem, or if they are a carrier and might pass it on. With a one gene test, you can find out if your dog has the potential to develop a certain illness. We want to emphasize the word potential here because as we said before, many genetic problems have multiple factors that influence whether a gene will ultimately be expressed.

There are two ways to approach disease genetic testing. One is do breed-specific tests. For example, if your dog is a Border Collie, you should have them screened for the MDR1 gene. This gene influences how your dog’s body processes certain drugs, including ones commonly used for chemotherapy, diarrhea and deworming. Dogs who have a mutation for this gene can respond negatively if given some of those medications which other dogs (without the gene) can handle easily.

The second way is to do a general screening for all potential disease-associated genes. That may give you some information you don’t really need, but would hopefully catch any problems you may not have considered.

“I would recommend a full genetic panel,” Boyko said. “Generally, the costs are on par or even less expensive than doing single-gene tests for all the breed-relevant health and trait conditions. Screening for all known genetic conditions also allows breeders to discover new mutations within their breed that have historically not been problematic, if they crop up. And knowing the expected coefficient of inbreeding, or COI, of breeding pairs and confirming pedigree relationships is also valuable.”

Breed-specific tests

There are many breed-specific tests for various genetic mutations. Some of these tests are only offered by the universities or companies that developed the test. For example, the University of Wisconsin School of Veterinary Medicine has a test that looks at the risk of cranial cruciate ligament (CCL) rupture (when the ligament in the knee is injured or torn) in Labrador Retrievers.

This is not a simple one-gene test. Instead, the testing laboratory evaluates your dog’s genome for a variety of genetic markers. The results are analyzed with bioinformatics to develop a unique disease risk profile for each dog.

Environmental factors will also play a role in your dog’s long-term risk. For example, if your dog is overweight and participating in high-impact sports, they will naturally have a higher risk for CCL, with or without the gene. Still, a heads up could help you plan your dog’s lifestyle to minimize the risks of this injury.

Even the same defect can be caused by a different series of mutations, depending on the individual dog or the breed.

PRA, progressive retinal atrophy, occurs in a wide variety of breeds. Some breeds share the same genetic defect that leads to blindness, while others have a mutation that ultimately leads to the same problem. After the genetic mutation associated with a breed is found, researchers then look at other breeds known to have a similar health problem and see if the genetic defect matches.

For the future

As we learn more about inheritance and genetics, more testing will become available for our canine companions. Testing can help with planned breedings to minimize risks of illness. It can also alert people to potential health risks that their dog may develop so they can take steps to modify their dog’s lifestyle.

Genetic findings in canine health can also be used for studying similarities in human conditions, such as in the field of comparative oncology (cancer).

“Developing tests that can identify dogs with high risks for cancer will be hugely important, especially as our ability to screen and treat cancer in dogs continues to improve,” Boyko said. “There are also cardiac diseases, orthopedic diseases and autoimmune diseases where genetic screening has the potential to become quite important in the future. Eventually, I think, genetic screening will be invaluable for more than just assessing health risks, and it will be commonly used to assess behavioral predispositions and guide decisions for training — as well as our recommendations for nutrition, supplements and medications.”

Back in 2001, Cornell was involved in one of the first cases of using genetic therapy to treat an inherited canine disease. Briards who have young dog congenital stationary night blindness (or impaired night vision) were successfully treated with gene therapy. This disease is similar to a disease in human infants called called Leber congenital amaurosis that causes blindness at birth, and now studies are underway to help human patients with their version of this problem.

In addition to providing valuable health and trait information, genetic testing helps support the future of a breed and the health of all dogs. When we integrate this information into a digital biobank (where every dog is tested on a research-grade genotyping array), it allows the data to be freely downloaded by owners, breeders and researchers to make future genetic discoveries.

These genetic data, coupled with health data from other surveys or veterinary records, sets the future of breeding up for success. It puts us in the best possible position for quickly identifying specific genetic defects when they crop up in a breed, and it enables researchers to develop the tests needed to reduce the impact and prevalence of these disorders.

The Orthopedic Foundation for Animals maintains a list of canine genetic testing laboratories in North America and Europe to help people learn more about the tests that already exist.

This article has been reprinted with permission from the Cornell University College of Veterinary Medicine’s DogWatch newsletter, published by Belvoir Media Group. When you become a member of the Riney Canine Health Center, you will receive a free subscription to DogWatch.