Equine malignant hyperthermia (EMH)
Equine malignant hyperthermia (EMH) is a dominant disease (one copy of the mutation is sufficient to produce disease) identified in Quarter Horses and American Paint Horses that can cause severe typing up and even death when horses are subjected to anesthesia.
It has been shown that a gene mutation in the calcium release channel causes a dysfunction in skeletal muscles resulting in excessive release of calcium inside the muscle cell. This triggers a series of events resulting in a hyper-metabolic state and/or death. Symptoms include fever, excessive sweating, elevated heart rate, abnormal heart rhythm, shallow breathing, muscle rigidity, and death with acute rigor mortis.
Tying up can occur in some horses without anesthesia and can increase the severity of signs in horses who also have Polysaccharide Storage Myopathy (PSSM).