Allele Frequencies and Genotypes for the Ryanodine Receptor 1 Variant Causing Malignant Hyperthermia and Fatal Rhabdomyolysis With Hyperthermia in Horses.

Summary

# Editorial Summary: RYR1 Malignant Hyperthermia in Quarter Horses A missense mutation in the ryanodine receptor 1 gene (RYR1 p.R2454G) has been identified as the causative variant for fatal malignant hyperthermia and exertional rhabdomyolysis with hyperthermia in Quarter Horses, a life-threatening condition previously recognised only in individual case reports. Aleman and colleagues characterised allele frequencies and genotype distributions across Quarter Horse populations to establish the prevalence of this mutation and assessed carrier status in animals with and without clinical disease history. All documented cases to date presented as heterozygotes, with the allele frequency remaining low within the breed, though the authors' work quantifies this distribution more precisely than earlier anecdotal evidence. For equine professionals, this research enables more informed genetic risk assessment and counselling—particularly for anaesthesia protocols, as affected heterozygous horses pose serious perioperative risk—and provides a foundation for potential selective breeding strategies if breeders wish to avoid propagating this variant. Given the mutation's severity and the availability of genetic testing, identifying carrier status before anaesthesia or intensive exercise becomes an increasingly practical preventative measure in Quarter Horse management.

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Key Findings

• •A missense variant in RYR1 gene (p.R2454G) causes fatal malignant hyperthermia and rhabdomyolysis with hyperthermia in Quarter Horses
• •All reported cases to date have been heterozygous for the MH variant
• •The allele frequency for this RYR1 variant is suspected to be low in the Quarter Horse population

Conditions Studied

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