Autosomal dominant canine malignant hyperthermia is caused by a mutation in the gene encoding the skeletal muscle calcium release channel (RYR1)

Background: Malignant hyperthermia (MH) is an inherited disorder of skeleta l muscle characterized by hypercarbia, rhabdomyolysis, generalized skeletal muscle contracture, cardiac dysrhythmia, and renal failure, that develops on exposure to succinylcholine or volatile anesthetic agents. All swine and up to 50% of human MH events are thought to be associated with mutations i n the calcium release channel of the sarcoplasmic reticulum, also known as the ryanodine receptor (RYR1). Events resembling MH have been reported in o ther species, but none have undergone genetic investigation to date. Methods: To determine the molecular basis of canine MH, a breeding colony w as established with a male, mixed-breed, MH-susceptible (MHS) dog that surv ived an in vivo halothane-succinylcholine challenge. He was mated to three unaffected females to produce four litters and back-crossed to an affected daughter to produce one litter. One of his MHS sons was mated to an unaffec ted female to produce an additional Utter. Forty-seven dogs were phenotyped with an in vitro contracture test and diagnosed as MHS or MH normal based on the North American in vitro contracture test protocol. Nine microsatelli te markers in the vicinity of RYR1 on canine chromosome 1 (CFA01) were test ed for linkage to the MHS phenotype. Mutational analysis in two MHS and two MH-normal dogs was performed with direct sequencing of polymerase chain re action products and of cloned fragments that represent frequently mutated h uman RYR1 regions. A restriction fragment length polymorphism was chosen to detect the candidate mutation in the pedigree at large. Results: Pedigree inspection revealed that MHS in this colony is transmitte d as an autosomal dominant trait. FH2294, the marker closest to RYR1, is li nked to MHS at a theta = 0.03 with a LOD score of 9.24. A T1640C mutation g ives rise to an alanine for valine substitution of amino acid 547 in the RY R1 protein, generating a maximum LOD score of 12.29 at theta = 0.00. All do gs diagnosed as MHS by in vitro contracture test were heterozygous for the mutation, and all MH-normal dogs were homozygous for the T1640 allele. Conclusions: These results indicate that autosomal dominant canine MH is ca used by a mutation in the gene encoding the skeletal muscle calcium release channel and that the MHS trait in this pedigree of mixed-breed dogs is in perfect cosegregation with the RYR1 V547A mutation.