In vitro contracture test and gene typing in diagnosing malignant hyperthermia

Background: Malignant hyperthermia (MH) is an autosomal dominantly inherited disorder,triggered in susceptible individuals by inhalation anesthetics and depolarizing muscle relaxants such as succinylcholine. Because of its high sensitivity (97-99%) and specificity (93,6%) as well as the genetic heterogeneity of MH disorder, the in vitro contracture test (IVCT) following the European-MH-Group is considered to be the "Gold Standard" for phenotypical determination of predisposed patients. On the other hand mutations in the skeletal muscle ryanodine receptor gene (RYR1) are tightly linked with MH susceptibility. After detecting a C1840T-mutation (Arg614Cys) in the RYR1 gene in one individual of a large MH family, we searched far this mutation in the remaining family members and determined the concordance with IVCT. Methods: According to the European standard protocol for MH, 43 individuals of a large MH pedigree were assigned the status of MH susceptible (MHS), - negative (MHN) or - equivocal (MHE). The genetic investigation of 44 family members for the Arg614Cys-mutation was carried out by restriction fragment analysis:Genomic DNA was prepared from EDTA whole blood followed by amplification of a 918 bp RYR1 gene fragment by polymerase chain reaction. In presence of the Arg614Cys-mutation digestion with the restriction endonuclease RsaI would result in different DNA fragments of the amplified sequence than in absence of mutation. Results: According to the response to IVCT, 25 individuals phenotypically revealed MHS, 7 MHE and 11 MHN status. Out of the 44 family members screened genetically for the Arg614Cys-mutation, the mutation was detected in 23 individuals. Out of them 19 were MHS and one was MHEc. The mutation was absent in 9 predisposed individuals, but six of them were MHE and three MHS. The mutation was also present in three individuals who had no MH screening (IVCT) before. For these last mentioned individuals the diagnosis MHS was deduced from genetic results. Conclusion: Based on results of IVCT the identification of a MH associated mutation in a MH-family can make and support a correct MH diagnosis and can resolve MHE findings.