When Petunia, a 13-year-old pug, began having trouble walking and controlling her bladder and bowels, her owners wanted to get to the bottom of the cause. So they bought a direct-to-consumer $65 genetic test specifically for dogs. The results were shocking: Petunia (not her real name) carried a mutation linked to a neurodegenerative condition similar to amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease).
To save their beloved dog from suffering progressive and irreversible paralysis before dying (as happens with this ALS-like disease), the owners had Petunia "put to sleep."
Now, scientists are saying that Petunia might not have even developed the disease. In fact, as few as 1 in 100 dogs with the mutation develop the rare disease, research shows. Moreover, Petunia's symptoms were consistent with a more-treatable spinal disorder, say scientists who are urging pet owners to steer clear of consumer DNA testing for the purposes of making medical decisions for their furry family members. [20 Weird Dog and Cat Behaviors Explained by Science]
That's because scientists are far from understanding the mysteries of dog genetics, said the authors of the article, published online today (July 25) in the journal Nature.
"Genetics is a really powerful, new tool, but it really is a new tool, and we don't understand what it means yet," study senior author Elinor Karlsson, an assistant professor of molecular medicine at the University of Massachusetts Medical School in Worcester, told Live Science.
Petunia's case isn't an isolated one, said study co-author Dr. Lisa Moses, a veterinarian at the Massachusetts Society for the Prevention of Cruelty to Animals-Angell Animal Medical Center and a research fellow of bioethics at Harvard Medical School. More vets and pet owners are now relying on genetic testing results "to make pretty important medical decisions about their pets, including truly life-and-death decisions," Moses told Live Science.
Even though the science behind doggy genetic testing is lagging, the market is booming. Worldwide, there are at least 19 laboratories that market genetic-testing products for dogs, the authors said. These tests often cost less than $200 and claim to reveal the genetic risk for more than 100 diseases. One U.S. veterinary hospital chain even recommends genetic testing for all dogs, claiming the tests can inform "individualized health care" and guide behavioral training for each pooch, the authors wrote in the perspective piece.
But to tease apart which mutation or combination of mutations can lead to health conditions, scientists must run huge genetic-testing studies with tens of thousands of participants, Karlsson said. Despite this, most of the pooch-related research is based on small, underpowered studies, she and her colleagues said. [How Do DNA Ancestry Tests Really Work?]
"Neither their accuracy nor their ability to predict health outcomes has been validated," the authors wrote in the perspective. "Most vets don't know enough about the limitations of the studies, or about genetics in general, to be able to advise worried owners."
For example, a genetic study might find that dogs with a medical condition have a specific genetic mutation. But the next step — which most canid researchers have yet to do — is to get a new pool of dogs to test how many with the mutation go on to develop the condition, Karlsson said.
This step would allow researchers to determine "whether, based on that genetic change, you can predict which dogs get the disease," Karlsson said. "That's the piece that we're missing. It's really important if you're going to use [the results] clinically." [7 Diseases You Can Learn About from a Genetic Test]
To improve genetic testing for dogs, the authors recommended several steps that could be implemented immediately. These include sharing studies on pet genetics (right now, most industry studies are private, meaning other researchers can't read and evaluate the results) and training pet genetic counselors who could explain pet test results to vets and pet owners.
The industry should also create a standard methodology for testing dog genetics — for example, outlining how samples should be collected, shipped and analyzed, the authors said. Pet studies should also have a certain number of participants before claims are made about the results, the authors added.
And, if a gene is suspected of increasing the risk for a medical condition, the company could indicate on a scale of 1 to 5 just how serious this risk is, and what the evidence says about it, Karlsson said.
These changes won't benefit only dogs but also human health, because dogs are now being used as models for studying human diseases, such as Alzheimer's and cancer, Karlsson said.
Should you test your pet?
As for whether pet owners should get tests for their dogs or even cats (there are fewer tests for cats, but the field is growing), the researchers said it depends on what kind of person you are. If you take the results with a grain of salt, meaning you realize that they might be an indication but not an absolute picture of your pet's health, then go for it, Karlsson said.
But, if you might see the results as a life-or-death sentence for your pet, then it's probably best to wait for the research to mature, Karlsson said.
Either way, pet owners should be cautious about using these tests to make medical decisions about their pets, Moses said. For now, "the scientific and industry communities need to set up some basic standards to ensure that we know what the tests really mean," Moses said.
Original article on Live Science.