Genetics for Horses and Humans: We are more alike than you think!

Horses and humans go way back–humans first domesticated horses somewhere around 6,000 years ago. But it’s not just our history that we share, as mammals, it’s also our DNA. Because we share a common genetic code many of the hereditary diseases affecting horses are also found in humans. One such example is Waardenburg syndrome, another is malignant hyperthermia.

Malignant hyperthermia, or MH, is a condition where muscles contract too hard and too long (muscle rigidity) in response to a certain trigger. This leads to potentially deadly complications like high heart rate and an abnormal rhythm, dangerous rise in body temperature (hyperthermia), and ultimately muscle damage. The trigger is often a certain type of medication used in general anesthesia, so both horse and human with this condition may not discover the danger until suffering an episode while being prepared for a surgery. Once MH has been diagnosed, different medications can be used for any general anesthesia needed in the future to avoid these complications. In horses, and less often in humans, extreme exercise, exposure to extreme heat, or other physical stress can also trigger an MH episode, which, if unrecognized, can be fatal.

MH is caused by a mutation in a gene called RYR1. This mutation (a change that causes the normal gene to stop working) can be passed down from parent to offspring, so the disease tends to run in families. In horses, MH has so far been found primarily in Quarter Horses however other breeds could also be affected. Testing for MH in horses is becoming more common to avoid unfortunate surprises during stress or anesthesia. Even people with MH may not know the mutation runs in their family, simply because so many go their entire lives never needing general anesthesia!

Owners of Quarter Horses and other breeds may want to consider testing for MH even if their horse has never needed surgery.Knowing ahead of time could save a horse’s life should they undergo general anesthesia at some point in the future. Learn more about testing here.

If you have a relative who has MH or has experienced a bad reaction to anesthesia, you can find out more about your risk (and get genetic testing if you need it) by consulting a genetic counselor. A genetic counselor is a health care professional who helps people understand and adapt to the impact of genetics on their health, including assessing the need for genetic testing. You can find a genetic counselor near you at findageneticcounselor.nsgc.org. November is also Family History Month! Gathering with your loved ones for Thanksgiving is a great time to check in about each other’s health and find out if there are any conditions in your family that might be hereditary. Read more about the importance of knowing your family health history.

Oh, and by the way: Even though horses and humans have many of the same genes, there are enough small differences in those genes that you cannot use a genetic test for horses on humans, or vice versa!

Written by Leslie Ordal, MSc, CGC, a board-certified genetic counselor and the Assistant Director of the Master’s in Genetic Counseling program at Boise State University (go Broncos!). An avid equestrian since age 10, she enjoys dressage and trail riding with her two sport ponies.