UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory

Malignant Hyperthermia(MH)


Malignant hyperthermia (MH) is an inherited autosomal dominant disease that causes a life-threatening condition in susceptible horses triggered by exposure to halogenated anesthetics or succinylcholine, and occasionally by stress or excitement. This genetic condition has been identified in Quarter Horses and American Paint Horses. A genetic defect in the calcium release channel that results in excessive release of calcium inside skeletal muscle cells which then triggers a hyper-metabolic state that can be fatal.  Signs of MH episodes include muscle contracture (rigidity), elevated body temperature (> 40°C), elevated heart rate, irregular heart rhythm, excessive sweating and shallow breathing. Presence of the MH mutation also results in more severe clinical tying-up phenotype in horses that have the PSSM1 mutation.

The diagnostic DNA test for MH allows identification of horses that have this mutation and are at risk of developing clinical signs of the disease, especially if subjected to anesthesia. This test is recommended for Quarter Horses, Paints and related breeds. The DNA test will also assist veterinarians to use appropriate medication for surgical procedures and make the correct diagnosis of the cause of a tying-up event.

Allow 2-6 business days for results.

Results reported as:

N/N: Normal - horse does not have the MH gene

N/MH: Affected - horse has one copy of the MH gene

MH/MH: Affected - horse has two copies of the MH gene


Aleman M, J Riehl , BM Aldridge, RA Lecouteur, JL Stott, IN Pessah. Association of a mutation in the ryanodine receptor 1 gene with equine malignant hyperthermia. Muscle Nerve 30(3):356-65, 2004.

Aleman M, JE Nieto, KG Magdesian. Malignant hyperthermia associated with ryanodine receptor 1 (C7360G) mutation in Quarter Horses. J Vet Intern Med. 23(2):329-34, 2009.

Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL