Background: Malignant hyperthermia susceptibility (MHS) is a life-threatening, inherited disorder of muscle calcium metabolism, triggered by anesthetics and depolarizing muscle relaxants. An unselected cohort was screened for MHS mutations using exome sequencing. The aim of this study was to pilot a strategy for the RYR1 and CACNA1S genes. Methods: Exome sequencing was performed on 870 volunteers not ascertained for MHS. Variants in RYR1 and CACNA1S were annotated using an algorithm that filtered results based on mutation type, frequency, and information in mutation databases. Variants were scored on a six-point pathogenicity scale. Medical histories and pedigrees were reviewed for malignant hyperthermia and related disorders. Results: The authors identified 70 RYR1 and 53 CACNA1S variants among 870 exomes. Sixty-three RYR1 and 41 CACNA1S variants passed the quality and frequency metrics but the authors excluded synonymous variants. In RYR1, the authors identified 65 missense mutations, one nonsense, two that affected splicing, and one non-frameshift indel. In CACNA1S, 48 missense, one frameshift deletion, one splicing, and one non-frameshift indel were identified. RYR1 variants predicted to be pathogenic for MHS were found in three participants without medical or family histories of MHS. Numerous variants, previously described as pathogenic in mutation databases, were reclassified by the authors as being of unknown pathogenicity. Conclusions: Exome sequencing can identify asymptomatic patients at risk for MHS, although the interpretation of exome variants can be challenging. The use of exome sequencing in unselected cohorts is an important tool to understand the prevalence and penetrance of MHS, a critical challenge for the field. hyperkalemia, as well some or all of the following symptoms: tachycardia, tachypnea, arrhythmias, skeletal muscle rigidity, and lethal hyperthermia. It is inherited in a predominately autosomal dominant pattern and associated with RYR1 or CACNA1S mutations, with other mapped loci. Seventy to 86% of patients with MHS have RYR1 mutations1-5 and 1% have CACNA1S mutations.6 The prevalence and penetrance of MHS mutations are difficult to determine because the pharmacologic exposure rate is low and it is an inconsistently manifesting gene-environment interaction; that is, when a susceptible patient is exposed to a triggering agent, the probability of malignant hyperthermia (MH) is less than 100%. Most MHS gene and variant studies have been performed on families with multiple generations affected with typical MHS. Studying these families made possible the discovery of the two implicated genes. However, these studies had ascertainment biases for those with severe reactions to the drugs. This has complicated efforts to establish the true prevalence and penetrance of MHS mutations. In addition, assigning pathogenicity to RYR1 and CACNA1S variants is challenging for several reasons. First is the issue of locus heterogeneity. With several mapped loci without identified genes, some RYR1 and CACNA1S variants may have been erroneously determined to be pathogenic when there was a causative variant in another (untested) gene. In addition, RYR1 and CACNA1S are large genes with 106 and 44 exons, respectively, making mutation screening challenging. Thus, some RYR1 and CACNA1S variants previously determined to be pathogenic may be benign, as has been shown for other genes.7 New sequencing technologies, including exome sequencing (ES), have made sequencing of the human exome (exons of known genes) feasible. This provides the opportunity to detect mutations in MHS genes in a less biased manner. Using this approach, we can improve our understanding of the mutational spectra of the RYR1 and CACNA1S genes, and estimate their penetrance. Our objective was to identify mutations in RYR1 and CACNA1S in a population not ascertained for MHS, as a pilot for the use of exome data for predictive medicine.
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