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veterinarians look for when trying to determine the cause of a muscle problem. “Awareness has increased and more veterinarians might think about this, but usually the owners spend a lot of money on a lameness exam before they get around to genetic testing,” says Finno.
“Being able to use the tests for diagnostics and pre-purchase exams is helpful for sports such as roping, racing or barrel racing. Unfortunately, a performance-limiting trait may also come across as a behavioral issue because the horse is uncomfort- able and doesn’t want to work. In these situations, we need to make sure we’ve ruled out everything else, including genetic diseases, before we assume it’s a training issue,” says Finno.
“In terms of the cost of horses and keeping horses, cost of testing is minimal,” she says. “You have also saved your veterinarian a step-in diagnos- tics if the horse ever has a performance problem. You’d have those results, so later if your horse does have a problem, you can tell your vet that you know it’s not this, this, or this,” she says.
MAKE SURE YOU USE VALIDATED TESTS
“Another issue is whether the genetic tests have been validated,” says Valberg. “All 5 tests offered by AQHA have been identified, published and validated by other scientists, and known to be accurate reflec- tion of disease. There are some other genetic tests now being offered, such as for type 2 PSSM, but to my knowledge there is no genetic mutation that has yet been published in the scientific literature and validated as causing type 2 PSSM.”
Winand also says there is no legitimate test at this time for what is being called type 2 PSSM. “Some companies claim to have a test, but have not yet published or disclosed anything about their test.”
Earlier, genetic tests were patented and only cer- tain labs could run a particular test. Now there are no longer any patents in the U.S. for genetic testing. There is no regulation of private labs for animal DNA testing. You are at the mercy of the lab, so you want to select one that you trust.
“That’s why a lot more labs are now testing,” says Winand. “This is a good thing and a bad thing. It’s good that there are more options for testing,
but the downside is that some labs appear to have significant error rates. That’s a huge concern, and that’s why AQHA uses the lab at UC-Davis because they are very confident in those results.”
Researchers put a lot of time and money into finding mutations and creating tests for them. Finno is concerned that equine genetic testing may be getting a “bad name” because some com- panies and individuals are offering tests that may not be validated.
“Once a genetic test is available to the public, cost of tests doesn’t completely reimburse the researcher for funds already invested,” Finno says. “Instead,
this money goes toward future research efforts. This research has made the tests available for the benefit
of the community. It’s important to use tests that are
Identified in 1985 and linked to the stallion Impressive (above), the genetic mutation hyperkalemic periodic paralysis (HYPP) affects muscle metabolism.
licensed and published.” You can have more faith in these because of the research and documentation. “Owners need to ask questions if they are not
using one of the well-established veterinary genetic testing laboratories such as UC-Davis Veterinary Genetics Laboratory,” says Finno. “If they go somewhere else because it’s cheaper, they need to be sure those labs are using the tests that are based on published mutations and have been validated. Using tests for diseases for which there is no mutation that’s been published provides an unverified and potentially inaccurate result.
“They are not all created equal. Check for qual- ity and accuracy. Don’t just cost shop. Reputable labs do everything possible to make sure results are accurate. Veterinary genetics labs are not regulated like human genetic testing.
There are millions of genetic variants in horses’ genes. It is important that the research is done to clearly connect an identified genetic variant with specific characteristics of the disease. “If a genetic discovery is valid, it stands up to the scrutiny of scientific publications,” Valberg explains. “If you don’t publicly identify genetic mutations and
just offer genetic tests, nobody knows whether it actually tests for a specific genetic disease or is just a common variant in a horse’s genetic code. This becomes very confusing for horse owners.
“In any breed, any species, there are genetic mutations,” she explains. “A horse may be hetero- zygous and inherit susceptibility to type 1 PSSM, which means one gene has the genetic mutation which came from one parent, and another gene from the other parent that doesn’t have the genetic muta- tion. In that situation, where a horse is heterozygous for that defect, you may see a variety of clinical signs in different individuals. Some horses are severely
affected when they have one gene that is abnormal and one that is normal, yet some horses may have minor signs or show no clinical signs,” she explains.
“In these situations, some people might say
the test isn’t accurate. The test is accurate in terms
of saying, yes, this horse has inherited this genetic mutation or no it has not. Yet there’s always a range of variability in the severity of clinical signs even though every horse that tests positive has the same genetic mutation. This is a bit dependent upon environmental influences on the gene, along with diet and exercise, and many other factors, like inter- action with the 20,000 other genes that horses have. Even though the genetic tests are fairly simple and the results are simple, there are still many other fac- tors that determine how severe the clinical signs are.”
It is important for horse owners to become knowledgeable about genetics and genetic testing. “Be aware of the three considerations for when
to use genetic testing: breeding, purchasing and diagnosis. Also be aware of what the genetic test is that is being offered, and whether a test has been validated,” Valberg says.
“For future research we are looking at the fact that some horses have underlying genetic suscep- tibilities, but it may be that a group of genes act together rather than one specific gene causing the disease,” she says. “Multiple interactions with other genes make it harder to find that specific cause. Since they are more complex and more complicated, it will require more detailed techniques and research and newer approaches before we can get to the bottom of them. There are still some diseases we suspect have an underlying genetic basis, but we have not yet been able to identify genes that are associated with them. There is still lots of research being done, to try to figure it all out. We are still learning,” she says.
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EQUINE HEALTH