Genetic link to muscle disease discovered; a vaccine for allergies
Immune-mediated myositis is a muscle disease seen in Quarter Horses and related breeds such as Paints and Appaloosas. It can lead quickly to muscle weakness and atrophy and can leave your horse feeling generally ill. Unfortunately, not a lot has been known about the cause of IMM. New research, though, shows there is likely a genetic link.
A team led by Carrie Finno, DVM, PhD, DACVIM, assistant professor in the department of population health and reproduction at the University of California, Davis, set out to examine genetic aspects of the disease. The team included Stephanie J. Valberg, DVM, PhD, DACVIM, ACVSMR, from the department of large animal clinical sciences at Michigan State University, and colleagues from both universities as well as from the University of Minnesota.
The researchers gathered DNA samples from three groups of horses:
36 Quarter Horses with a history of IMM
54 Quarter Horses with no history of IMM 175 horses from 21 other breeds. Each group was a mix of geldings, mares and stallions with approximately the same average age range. All were housed in the same environment. Any horses with polysaccharide storage myopathy (another muscle disease particularly found in Quarter Horses) were excluded from the study. None of the horses were related to each other within at least one generation.
After extensive analysis of the DNA samples, the team identified a mutation in the MYH1 gene. This gene is related to the protein myosin, which plays a role in muscle contraction. The mutation affected 14 different amino acids in the protein. Specifically, it appeared to destroy Type II (slow-twitch) muscle fibers, leading to the disease’s characteristic muscle atrophy.
Notably, the mutation was not found among the 175 horses from non-Quarter Horse breeds. This supports the idea that IMM may be an issue only for Quarter Horses and related breeds.
The researchers also analyzed the horses’ pedigrees and found that certain stallions were heavily represented among the horses showing the mutation, indicating that IMM has a genetic component.
However, researchers do not necessarily believe that the MYH1 mutation directly causes IMM. Rather, horses with the mutation are more likely to experience active symptoms of the disease under certain circumstances. For instance, this could include age, as IMM is more likely to affect horses under age 8 or over age 17. And, according to past studies, there may also be a connection between IMM symptoms and a recent history of certain types of infections or vaccinations.
On the bright side, IMM-affected horses generally regain full muscle mass after one to 10 weeks of corticosteroid treatment.
A Vaccine for Allergies
As if the distracting buzzing of flying insects wasn’t enough of a bother, bug bites are also a leading cause of allergic skin reactions in horses. In particularly bad cases, horses may be faced with swelling, skin flaking or thickening and even weeping, bleeding wounds. Now imagine if a simple vaccination could prevent all that unpleasantness.
That’s just what an international team of researchers believe they’ve developed. The participants included representatives from the Universities of Bern and Zurich (both in Switzerland), England’s Oxford University, the Latvian Biomedical Research & Study Center and private-sector partners.
An allergic reaction can occur when an insect, such as a mosquito, injects allergens while feeding on your horse. (An allergen is any substance that causes an allergic response.) In a nutshell, the allergen triggers a type of immune reaction in the horse’s body that includes sending an “itch” message to the brain as well as giving rise to other symptoms commonly associated with an allergy.
The researchers theorized that if they could block the internal triggers of the immune response, they could then prevent the allergic outcome. So they created a vaccine with two primary functions—control both the immune response and the related allergic reaction. To do this, the vaccine works to control T-cells and eosinophils, two types of white blood cells important to the immune system and allergic responses.
The team tested its vaccine on a herd of 34 Icelandic horses afflicted with chronic allergic reactions to insect bites. Nineteen of the horses were given the vaccine while 15 were given a placebo. All of the vaccinated horses showed clinical improvements, including reduced skin lesions compared to what they had experienced the previous year and compared to the placebo group. In addition, none of the horses showed adverse reactions to the vaccine. Considerably fewer horses in the placebo group showed improvement in their allergy symptoms.
The researchers believe this development could potentially change medical treatment for all pets, as it demonstrates the successful use of an immunotherapy for a chronic health issue. It may even assist in asthma therapy for humans. — Sushil Dulai Wenholz
Scientists have found a genetic link to the cause of immune-mediated myositis, a muscle disease often seen in Quarter Horses.
Researchers are working on a vaccine to alleviate allergic skin reactions that can be caused by insect bites.