Malignant hyperthermia associated with ryanodine receptor 1 (C7360G) mutation in Quarter Horses.
BACKGROUND
Anesthetic-induced malignant hyperthermia (MH) has been documented in Quarter Horses with a single point mutation in the ryanodine receptor 1 gene (RyR1) at nucleotide C7360G, generating a R2454G amino acid substitution. However, there have been no reports of nonanesthetic manifestations of MH in horses with the C7360G mutation.


OBJECTIVE
To describe clinical manifestations of Quarter Horses with the C7360G mutation.


METHODS
Eleven Quarter Horses with the RyR1 C7360G mutation.


METHODS
This prospective study included horses with suspected MH, undetermined etiology of sudden death, death within hours of onset of rhabdomyolysis, muscle rigidity, stiffness, intermittent sweating, and persistent increases in serum muscle enzyme activities. Whole blood in EDTA and skeletal muscle were processed for genetic and histochemical analysis. Medical records and pedigrees were collected when available.


RESULTS
Both anesthetic- and non-anesthetic-associated myopathic manifestations of MH occurred in halter Quarter Horses with mutation of RyR1. The disease is inherited as an autosomal dominant trait. Clinical and laboratory abnormalities were similar in both forms. Rhabdomyolysis was a common finding in both groups of horses. Skeletal muscle histochemical findings were nonspecific and compatible with a noninflammatory myopathic process.


CONCLUSIONS
MH is a potentially fatal disease of Quarter Horses that could be triggered by halogenated anesthetics and other nonanesthetic factors that may include exercise, stress, breeding, illnesses, and concurrent myopathies.
Aleman
M
M
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Tupper Hall 2108, One Shields Avenue, Davis, CA 95616, USA. mraleman@ucdavis.edu
Nieto
J E
JE
Magdesian
K G
KG
D000818:Animals; D004247:DNA / Q000737:chemistry / Q000235:genetics; D005260:Female; D006651:Histocytochemistry / Q000662:veterinary; D006734:Horse Diseases / Q000235:genetics*; D006736:Horses; D008297:Male; D008305:Malignant Hyperthermia / Q000235:genetics / Q000662:veterinary*; D017354:Point Mutation; D011446:Prospective Studies; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics*; D017422:Sequence Analysis, DNA
D019837:Ryanodine Receptor Calcium Release Channel; D004247:DNA