The origin of the degenerative and painful equine disease has so far remained elusive to scientists. However, it has been known to appear with some frequency in Thoroughbreds, Warmbloods, and stock-type breeds such as Paints and Quarter Horses. It is also more prevalent in larger horses, and previous research has shown that it runs in families. Combined, these data point to a genetic link, said Christa Lafayette, CEO of Etalon Diagnostics in Menlo Park, Calif.
Lafayette, a biotechnology and equestrian scientist, was inspired to discover this connection during a dinner conversation at the 2019 American Association of Equine Practitioners (AAEP) meeting in Denver, Colorado.
“I was sitting with amazing equine vets at AAEP, and I literally wrote on a napkin what we hoped we could solve by next year, and the genetics behind kissing the thorns was tops. list,” Lafayette said.
Shortly after returning from the AAEP, Lafayette teamed up with Beau Whitaker, DVM, of Brazos Valley Equine Hospital, Salado, Texas, and Kent Allen, DVM, of Virginia Equine Imaging, The Plains, who were also at this AAEP dinner table. – and several other engineers and researchers to tackle the task of finding the “kissing spine gene”.
The group genotyped 155 Warmblood and pedigree horses that had presented to participating veterinary clinics due to back pain and/or poor performance. Veterinary evaluations of the horses revealed that they ranged from severe grade 4 kiss thorns to no kiss thorns.
Genetics: a higher level of severity for each copy
The team identified an associated variant, or allele, for the kissing thorns on chromosome 25. This single nucleotide polymorphism (SNP) BIEC2-668062 is linked to an average one degree increase in kissing thorn severity for each of the two copies of the horse allele (one from each parent).
This allele was not correlated with height in horses, which appears to be a distinct and unique factor in kissing spines, Lafayette said.
It was, however, close to a gene already known in other species to be associated with the proliferation of chondrocytes (a cartilage-producing cell), a sign sometimes observed histopathologically (under the microscope) with kissing spines, a said Laura Patterson Rosa, DVM, PhD, scientific consultant at Etalon Diagnostics and first author of the group’s study publication. “It was reassuring to know that one of the ‘neighbor’ genes to our best marker was indeed involved before,” she said.
The allele discovered is not a causal to kiss the thorns, however. This is just one of many factors linked to the development of the condition, including exercise, rider skill and weight, riding equipment and fit, core muscle strength, riding position head and neck injuries and lameness, Lafayette said.
“This (genetic) correlation, we believe, is a risk variant for a higher degree or severity of thorn kisses and possibly for the development of the disease itself,” Lafayette said. Horse. “So instead of kissing grade 1 spines, for example, they’re more likely to have grades 3 or 4.”
Smarter breeding and competition with kissing thorns
Armed with this new knowledge, breeders and owners can make informed decisions about which horses carry the at-risk variant, Lafayette and Patterson Rosa said.
“For example, if I have a stallion and I know he has a high risk of passing on a variant that is correlated with kissing, then I might not pair him with a mare that has the same disposition, because then my chances are much higher that the resulting colt will have high quality spines,” she said.
As research continues, scientists may even find a causative mutation that may “give the power to ‘reproduce’ kissing thorns,” Patterson Rosa said.
When it comes to riding horses that have one or two copies of the kissing thorns risk variant, Lafayette suggested taking a proactive and protective approach. Having the variant does not mean they cannot continue working.
“Now let’s say you have a horse that you bought for eventing or Western riding or whatever you’re going to do, and you find it has a high risk of kissing thorns,” he said. -she explains. “So you’re probably going to spend a little more time doing back-strengthening exercises, maybe a little more dressage, maybe a little lighter on your back. You’re going to pay a little more attention to the fit of the saddle, and you might even get x-rayed a little more proactively, because you know this horse is more likely to suffer from a kiss on the spine vertebral.
The researchers stressed the importance of being able to work with real cases in veterinary clinics, with the collaboration of practitioners and owners. “We greatly appreciate how the community has embraced this effort,” Patterson Rosa said.
The study, Genomic loci associated with performance-limiting equine spinal processes (kissing the spines), first appeared in Research in veterinary sciences in June 2022.
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