Etalon Releases Chronic Anhidrosis Risk DNA Testing in Early Discovery Phase

Etalon Equine Genetics now offers early discovery phase testing for risk of Chronic Idiopathic Anhidrosis (CIA) in the horse. The presence of this variant indicates potential increased risk for developing chronic anhidrosis when exposed to environmental triggers, such as heat.

Here’s the quick and dirty on the condition and new testing available… Nerd Herd, read on for more scientific information. (Don’t worry, we’ll give you a warning before things get really technical!)

What is anhidrosis?

Also known as “non-sweater”, anhidrosis is the medical term describing a compromised or complete inability to sweat in response to increased body temperature.

This condition is dangerous and sometimes life-threatening for horses. Horses regulate their body temperature (thermoregulate) primarily through sweating, which is responsible for 65-70% of cooling, according to AAEP veterinarian Martha Mallicote DVM, Dipl. ACVIM. In the United States, cases of anhidrosis are more commonly observed in the hot and humid Southeastern regions. However, there are also reports in cooler climate regions like the Northern United States, Canada and even Ireland. Anhidrosis can affect several breeds of horses, although previous studies have demonstrated an increased incidence in Thoroughbreds and Warmbloods¹.

The condition can be acute: an isolated incident with a sudden onset, or chronic: repeated episodes that do not resolve with treatment of known triggers. Flared nostrils, an increased respiratory rate, and a lack of observable sweat after exercise are the most common initial findings. In situations that should cause copious sweating, affected animals produce minimal sweat – perhaps a small amount under the saddle pad – when all other horses are completely lathered. Severely affected horses might not even be able to tolerate turnout on hot days; they will stand in distress with an extremely high respiratory rate and body temperature as high as 104°F (40°C). Left untreated, hyperthermia in the horse due to anhidrosis can be fatal.

Can I DNA test my horse for chronic anhidrosis?

DNA testing for anhidrosis is now being offered by Etalon Diagnostics in an “early validation/discovery only” phase. This means that research findings are strong but require further validation. We recommend you include your veterinarian throughout the testing process to help interpret your horse’s results.

Here’s where things get a bit more complicated… buckle up for more on the science behind the condition, current research, and what your horse’s test results will look like.

What is the difference between chronic anhidrosis and acute anhidrosis?

Horses suffering from acute cases may exhibit an elevated respiratory rate and elevated body temperature, but most of these horses go back to sweating normally after treating the underlying condition. Acute cases can be caused by several factors including stress, as a side effect of some medications or antihistamines, electrolyte imbalance or hormonal issues.

In contrast, horses with chronic cases of anhidrosis - called “Chronic Idiopathic Anhidrosis” or CIA - have a long history of an insufficient sweat response, sometimes even all year long, and despite treatment of the known triggers mentioned above. For these horses, even moving to a cooler climate region may not help them recover the ability to sweat. The severe inability to thermoregulate puts CIA horses in danger of overheating, collapse and even death. You can learn more about anhidrosis here.

What recent research has been conducted on equine anhidrosis?

Studies conducted in Florida¹ found that horses with a family history of anhidrosis have over 21x higher odds of being affected with CIA. Recent work conducted by Dr. Laura Patterson Rosa at the University of Florida focused on the chronic form of the condition (CIA), and discovered a mutation in a potassium channel as the possible cause for CIA². Although hypothesized as a congenital potassium channel weakness, even chronic cases require exposure to conditions that induce exhaustion of the sweat response. For horses with CIA, sweat exhaustion may occur in response to conditions that are manageable for a normal horse, and may be accelerated by overworking, excessive sweating to control body temperature, and extreme heat conditions. Thus, these new genetic markers likely indicate an increased risk for development of CIA in response to environmental triggers.

With luck, further research might help us learn how to better prevent chronic anhidrosis in at-risk animals.

What will my horse’s test results look like?

Variant Definitions:

A/A - Lower than average risk of developing the chronic form of anhidrosis after environmental trigger exposures.

A/G - Moderate risk of developing the chronic form of anhidrosis after environmental trigger exposures.

G/G - Higher than average risk of developing the chronic form of anhidrosis after environmental trigger exposures. Please discuss proper management with your veterinarian.

References

¹Johnson EB, Mackay RJ, Hernandez JA. An epidemiologic study of anhidrosis in horses in Florida. J Am Vet Med Assoc. 2010 May 15;236(10):1091-7. doi: 10.2460/javma.236.10.1091. PMID: 20470071.

²Rosa LP, Walker N, Mallicote M, MacKay RJ, Brooks SA. Genomic Association of Chronic Idiopathic Anhidrosis to a Potassium Channel Subunit in a Large Animal Model. Journal of Investigative Dermatology. 2021 May 31. DOI: 10.1016/j.jid.2021.05.014