Genetic Prevalence of Variant for Immune-Mediated Myositosis and ER in Quarter Horses

A genetic test for the E321G MYH1 variant is now available, allowing veterinarians to diagnose IMM and non-ER with ease and providing horse owners with a tool to make informed breeding decisions and avoid producing affected foals.

Three-hundred seven elite performance Quarter Horses and 146 random registered Quarter Horse controls were included in the study.

The Journal of Veterinary Internal Medicine recently published the open-access article titled, “Prevalence of the E321G MYH1 variant for immune-mediated myositis and nonexertional rhabdomyolysis in performance subgroups of American Quarter Horses.” The study was authored by Giuliana M. Gianino, Stephanie J. Valberg, Sudeep Perumbakkam, Marisa L. Henry, Keri Gardner, Cecilia Penedo, and Carrie J. Finno.


The authors noted that, “Immune-mediated myositis (IMM) in American Quarter Horses causes acute muscle atrophy and lymphocytic infiltration of myofibers. Recently, an E321G mutation in a highly conserved region of the myosin heavy chain 1 (MYH1) gene was associated with susceptibility to IMM and nonexertional rhabdomyolysis. Objectives: To estimate prevalence of the E321G”

Conclusions and Clinical Importance

Knowing that reining and working cow Quarter Horses have the highest prevalence of the E321G MYH1 variant, and that the variant is more prevalent than the alleles for hereditary equine regional dermal asthenia and hyperkalemic periodic paralysis in the general Quarter Horse population, will guide the use of genetic testing for diagnostic and breeding purposes.”

You can access the article here.

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