A multi-dimensional analysis of genotype–phenotype discordance in malignant hyperthermia susceptibility

Background: Malignant hyperthermia (MH) susceptibility is an inherited condition, diagnosed either by the presence of a pathogenic genetic variant or by in vitro caffeine–halothane contracture testing. Through a multi-dimensional approach, we describe the implications of discordance between genetic and in vitro test results in a patient with a family history of possible MH. Methods: The patient, whose brother had a possible MH reaction, underwent the caffeine–halothane contracture test (CHCT) according to the North American MH Group protocol. Screening of the complete RYR1 and CACNA1S transcripts was done using Sanger sequencing. Additional functional analyses included skinned myofibre calcium-induced calcium release sensitivity, calcium signalling assays in cultured myotubes, and in silico evaluation of the effect of any genetic variants on their chemical environment. Results: The patient's CHCT result was negative but she carried an RYR1 variant c.1209C>G, p.Ile403Met, that is listed as pathogenic by the European Malignant Hyperthermia Group. Functional tests indicated a gain-of-function effect with a weak impact, and the variant was predicted to affect the folding stability of the 3D structure of the RyR1 protein. Based on American College of Medical Genetics and Genomics/Association of Molecular Pathology guidelines, this variant would be characterised as a variant of uncertain significance. Conclusions: Available data do not confirm or exclude an increased risk of MH for this patient. Further research is needed to correlate RyR1 functional assays, including the current gold standard testing for MH susceptibility, with clinical phenotypes. The pathogenicity of genetic variants associated with MH susceptibility should be re-evaluated