NEUROMUSCULAR CASE OF THE MONTH – OCTOBER 2008

Genetic test now available for malignant hyperthermia in horses
Contributed by Dr. Monica Aleman
Neuromuscular Disease Laboratory
University of California, Davis





Malignant hyperthermia (MH) is a potentially fatal disease when triggered by inhalant anesthetics such as halothane and isoflurane. However, other agents such as succinylcholine and caffeine can also trigger episodes. The disease has been reported or suspected in various breeds of horses and ponies. Recently, the genetic basis in Quarter Horses has been linked to a mutation in the ryanodine receptor 1 (RYR1, an intracellular calcium release channel) within muscle cells (Aleman et al, Muscle Nerve 2004;30:356-365). Horses with the mutation may be subclinical (no obvious signs) or develop clinical signs not associated with anesthesia. Based on our studies, affected horses can develop hyperthermia, sweating, stiffness, rhabdomyolysis (“tying up”), colic-like signs, elevated muscle enzymes, and death. The disease in the Quarter Horse is inherited as an autosomal dominant trait; therefore breeding affected horses may result in clinical signs regardless of lineage or breed. Studies on MH in horses are under way at University of California, Davis (UCD). The genetic defect was identified in our laboratory and testing is currently available (MH testing submission form). A publication detailing clinical aspects of MH in Quarter Horses will be available in early 2009.  

Examples of testing results and interpretation are shown below.
Negative for the mutation (no MH disease) = N/N
MH homozygous (affected horse) = MH/MH
MH heterozygous (affected horse) = N/MH

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Horse 1: N/N bred to horse 2: N/MH
50% offspring affected
 

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Horse 1: N/MH bred to horse 2 N/MH
75% offspring affected

 

For information on sample submission and testing contact:

Dr. Monica Aleman; MVZ Cert., PhD, Dipl. ACVIM
Neuromuscular Disease Laboratory, Director
Veterinary Medical Teaching Hospital
Large Animal Clinic
One Shields Avenue
University of California, Davis 95616
Telephone: + (530)-752-0290 (Hospital), or + (530)-752-1170 (NDL lab)
Fax: + (530)-752-9815 (Hospital)
E-mail: mraleman@ucdavis.edu

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