Breeds Affected: Most breeds
Samples Accepted: Blood, Hair
Disease Information: Symptoms of Malignant Hyperthermia include an elevated body temperature, muscle contractions and rigidity. Some affected horses show symptoms when under stress, and others only when exposed to anesthetics. MH can rapidly lead to death, making it very important to know if animals are normal before surgery or medical treatment. The presence of the RYR1 mutation can also modify (worsen) the symptoms of Polysaccharide Storage Myopathy (PSSM).
Inheritance Infromation: Malignant Hyperthermia is autosomal dominant, meaning that animals with only one copy of this allele will be affected, and will pass it on to 50% of its offspring.
The possible genotypes are:
n/n The horse is normal, and cannot produce affected offspring.
n/MH The horse is a carrier of MH, and can pass the allele on to approximately 50% of any offspring. There is a greater risk of being affected by itself.
MH/MH The horse is affected with MH. If bred to another horse (n/n or n/MH) 100% of the offspring will be affected. There is a extremely large risk of being affected by itself.
– Carriers and affected animals (m/m) should not be used for breeding
Test Information: This mutation test identifies a single base change in exon 46 of the RYR1 gene.
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 the Online Mendelian Inheritance in Animals website.