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Malignant Hyperthermia (MH)


→ Fever, muscle rigidity and respiratory distress triggered by anaesthetics or other stress.

Instructions for ordering:

  1. Enter the information of the first horse for which you want to order the test
  2. Add to cart
  3. Go to cart to check out, or
  4. Enter the information for a second horse
  5. For sample collection follow the instructions here.
  6. You can use this template to send in hair samples.
  7. Please also send the completed order form together with the samples.

For a breeder or veterinarian discount please contact us before ordering.

Any information you include here is optional, but will be included on the certificate of results.

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Is there anything else you would like to tell us about your horse? Reason for testing, symptoms etc.?

General Information

  • MH causes skeletal muscles to degenerate, which is associated with low blood pH (acidemia).
  • MH may worsen symptoms of PSSM (Polysaccharide Storage Myopathy).
  • In 34% of cases, MH results in death of the affected horse. Therefore, horses should be tested, especially prior to surgery or medical treatment.
  • Symptoms are not only triggered by anesthetics but also by stress and/or exercise.


  • Hyperthermia (fever)
  • Muscle rigidity
  • Respiratory distress
  • Excessive sweating
  • Increased hematocrit
  • Increased heart rate

Inheritance and Genotypes

→ MH is an autosomal dominant hereditary disease, meaning that horses with one or two copies of the genetic variant (n/MH or MH/MH) are affected.

Genotype: The horse is: Effects:
n/n normal. The horse does not have any copies of the genetic variant causative for MH and therefore cannot pass it on to any offspring.
n/MH affected (heterozygous).
The genetic variant causative for MH will be passed on to its offspring with a probability of 50%. These foals will also be affected (n/MH).
MH/MH affected (homozygous). The genetic variant causative for MH will be passed on to all offspring. All offspring will also be affected (n/MH).


  • Affected horses (n/MH or MH/MH) should not be used for breeding.


Aleman, M., Riehl, J., Aldridge, BM., LeCouteur, RA., Stott, JL., Pessah, IN.: Association of a mutation in the ryanodine receptor 1 gene with equine malignant hyperthermia. Muscle Nerve 30:356-65, 2004. Pubmed reference: 15318347. Doi: 10.1002/mus.20084.

Aleman, M., Nieto, JE., Magdesian, KG.: Malignant hyperthermia associated with ryanodine receptor 1 (C7360G) mutation in Quarter Horses. J Vet Intern Med 23:329-34, 2009. Pubmed reference: 19220734. Doi: 10.1111/j.1939-1676.2009.0274.x.

McCue, ME., Valberg, SJ., Jackson, M., Borgia, L., Lucio, M., Mickelson, JR.: Polysaccharide storage myopathy phenotype in quarter horse-related breeds is modified by the presence of an RYR1 mutation. Neuromuscul Disord 19:37-43, 2009. Pubmed reference: 19056269. Doi: 10.1016/j.nmd.2008.10.001

Further information is available at Online Mendelian Inheritance in Animals.

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