Peer-reviewed veterinary case report
Frequency of Malignant Hyperthermia Gene Variant in Horses
By Aleman, Monica et al.·Published in Journal of Veterinary Internal Medicine·2025·School of Veterinary Medicine, University of California Department of Medicine and Epidemiology, , Davis, California,, United States·View original on Crossref →
PetCaseFinder translated the abstract of this peer-reviewed paper into plain English so pet owners can read it. We do not publish original research — every detail traces back to the citation above. How we work →
Original publication title: Allele Frequencies and Genotypes for the Ryanodine Receptor 1 Variant Causing Malignant Hyperthermia and Fatal Rhabdomyolysis With Hyperthermia in Horses
- Species:
- horse
Plain-English summary
A group of Quarter Horses and other breeds were studied to understand a genetic variant that can cause dangerous reactions during anesthesia, known as malignant hyperthermia (MH). In this study, 51% of horses with the MH variant experienced severe complications, including death, when anesthetized. Most of the affected horses were young males, and no horses with two copies of the MH gene variant were found, suggesting they may not survive. The findings highlight the importance of genetic testing for horses that may undergo anesthesia, especially if they show signs of stress or illness.
People also search for: Quarter Horse anesthesia risks · malignant hyperthermia in horses · horse genetic testing for anesthesia safety
Abstract
Abstract Background Fatal anesthesia-induced malignant hyperthermia (MH) and rhabdomyolysis with hyperthermia documented in Quarter Horses (QH) breeds are caused by a missense variant in the ryanodine receptor 1 gene (RYR1: XP_023505430.1.:p.(R2454G), designated as MH). The reported cases to date have all been heterozygous, and the allele frequency is suspected to be low. Objective To determine an accurate estimate of MH allele frequency in multiple horse breeds and investigate whether homozygous animals exist in the population. Animals In total, 159 227 horses from 16 breeds who were either submitted for clinical evaluation (n = 1500) or genetic testing (n = 157 727) were included. Methods Prospective study using banked DNA samples from two diagnostic laboratories determined the presence, zygosity, and estimated population MH allele frequencies. Results The MH allele was exclusively detected in 391 QH, 18 Paints (PT), one Appaloosa (AP), and one QH-Clydesdale cross with similar allele frequencies (QH = 0.0013 and PT and AP = 0.0012). In cases submitted for clinical evaluation, death occurred as anesthesia-induced MH or severe acute rhabdomyolysis with hyperthermia (≥ 42°C, 107.6°F) in 51% of N/MH horses. Nineteen of the 20 fatal cases were young males (median: 9 years old, range: 9 months–14 years). No MH homozygotes were detected in either cohort evaluated. Conclusions and Clinical Importance Homozygotes for the MH allele were not identified, and thus might be incompatible with life, but additional testing is needed to confirm. Although the allele frequency was low, being heterozygous poses a risk of death if anesthesia, stress, concurrent illness, breeding, or other stresses occur.
Find similar cases for your pet
PetCaseFinder finds other peer-reviewed reports of pets with the same symptoms, plus a plain-English summary of what was tried across them.
Search related cases →Original publication on Crossref: https://doi.org/10.1111/jvim.70081