Genetics and tendon injury

Superficial digital flexor (SDF) tendon injury is a common cause of wastage in National Hunt Thoroughbred (TB) horses – leading to training and racing days lost and early retirement.

Recent research, funded by the Horserace Betting Levy Board, explored whether genetic susceptibility is a potential risk factor for SDF tendon damage in the TB racehorse.

The work, by Lucinda Tully and colleagues, compared the genotype of horses with and without SDF tendinitis in a case-control study.

Tully looked specifically at single nucleotide polymorphisms (SNPs) in seven genes that are involved in tendon structure, function, and remodelling or are known to be involved in Achilles tendinopathy (an equivalent condition in humans).

Genetic material for the study was derived from mane hair, or peripheral blood cells, collected from 270 horses with a history of SDFT strain, and 270 unaffected control samples, chosen at random from among the other horses on yards with affected cases.

The study's findings suggest that sequence variants in TNC and COL5A1 genes are associated with SDF tendinopathy in TB racehorses.

A SNP in COL5A1 significantly increased the odds of having SDF tendinitis. Racehorses having two copies of the COL5A1 COL5A1_01 variant allele were nearly 3 times more likely to have SDF tendinopathy than those homozygous for the wild-type allele.

Conversely , a SNP in the TNC gene was associated with significantly lower odds of SDFT injury. Racehorses heterozygous for the TNC BIEC2-696469 polymorphism were less likely to have SDF tendinopathy than those with two copies of the wild-type allele.

The research team conclude that variants in the TNC and COL5A1 genes are associated with SDF tendinopathy in a population of UK trained NH TB racehorses.

They suggest that further studies in a larger group of horses are needed to determine the significance of these findings at the population level.

In the future it may be possible to use genetic markers to identify horses at risk of SDF tendinopathy.

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