Malignant Hyperthermia (MH)

Malignant hyperthermia (MH) is a muscle disorder in which anaesthesia, stress, or extreme exercise trigger a hypothermic state. Symptoms include high temperature, increased heart rate, high blood pressure, sweating, acidosis, and muscle rigidity. If symptoms are not immediately resolved, death is likely to occur. As this condition is autosomal dominant, even horses with a single allele (MH/N) exhibit symptoms. One study has shown that horses with both MH and polysaccharide storage myopathy (PSSM) have more severe clinical symptoms.

RYR1 is involved in the control of calcium channels within the muscle. Mutations in both humans and swine have been shown to cause conditions similar to MH seen in the horse. This mutation is a single base substitution that alters an amino acid, likely affected the function of the encoded protein.

Publications

Aleman M et al., “Association of a mutation in the ryanodine receptor 1 gene with equine malignant hyperthermia.” (2004) Muscle Nerve. 30: 356-65. PMID: 15318347

McCue ME et al., “Polysaccharide storage myopathy phenotype in quarter horse-related breeds is modified by the presence of an RYR1 mutation.” (2009) Neuromuscul Disord. 19: 37-43. PMID: 19056269

Aleman M et al., “Malignant hyperthermia associated with ryanodine receptor 1 (C7360G) mutation in Quarter Horses.” (2009) J Vet Intern Med. 23: 329-34. PM: 19220734