DISCORDANCE, IN A MALIGNANT HYPERTHERMIA PEDIGREE, BETWEEN IN-VITRO CONTRACTURE-TEST PHENOTYPES AND HAPLOTYPES FOR THE MHS1 REGION ON CHROMOSOME 19Q12-13.2, COMPRISING THE C1840T TRANSITION IN THE RYR1 GENE

A point mutation in the gene encoding the skeletal muscle calcium release channel (RYR1) has been proposed as the probable cause of malignant hyperthermia (MH) in swine, where it segregates with the disease in all MH-prone strains investigated. The same C-to-T exchange in nucleotide position 1840 of the human RYR1 cDNA sequence was found in a few human MH pedigrees. We report a German MH pedigree where in vitro contracture test (IVCT) results and haplotypes of markers for the MHS1/RYR1 region including this base transition have yielded several discrepancies. The MH-susceptible phenotype was defined by IVCT performed according to the European standard protocol. Haplotypes were constructed for markers for the MHS1/RYR1 region on chromosome 19 and include the C1840T base exchange. Discussing the probabilities for a number of hypotheses to explain these data, we suggest that our results may challenge the causative role of this mutation-and possibly the role of the RYR1 gene itself-in human MH susceptibility, at least in some cases.