Safety of exposure of malignant hyperthermia non-susceptible patients and their relatives to anaesthetic triggering agents

Epidemiological and clinical features of malignant hyperthermia: A scoping review

Malignant hyperthermia (MH) is a potentially fatal inherited pharmacogenetic disorder related to pathogenic variants in the RYR1, CACNA1S, or STAC3 genes. Early recognition of the occurrence of MH and prompt medical treatment are indispensable to ensure a positive outcome. The purpose of this study was to provide valuable information for the early identification of MH by summarizing epidemiological and clinical features of MH. This scoping review followed the methodological framework recommended by Arksey and O'Malley. PubMed, Embase, and Web of science databases were searched for studies that evaluated the epidemical and clinical characteristics of MH. A total of 37 studies were included in this review, of which 26 were related to epidemiology and 24 were associated with clinical characteristics. The morbidity of MH varied from 0.18 per 100 000 to 3.9 per 100 000. The mortality was within the range of 0%-18.2%. Identified risk factors included sex, age, disorders associated with MH, and others. The most frequent initial clinical signs included hyperthermia, sinus tachycardia, and hypercarbia. The occurrence of certain signs, such as hypercapnia, delayed first temperature measurement, and peak temperature were associated with poor outcomes. The epidemiological and clinical features of MH varied considerably and some risk factors and typical clinical signs were identified. The main limitation of this review is that the treatment and management strategies were not assessed sufficiently due to limited information.

Identification and Functional Analysis of RYR1 Variants in a Family with a Suspected Myopathy and Associated Malignant Hyperthermia

BACKGROUND

The ryanodine receptor 1 (RyR1) is a major skeletal muscle calcium release channel located in the sarcoplasmic reticulum and involved in excitation-contraction coupling. Variants in the gene encoding RyR1 have been linked to a range of neuromuscular disorders including myopathies and malignant hyperthermia (MH).

OBJECTIVE

We have identified three RYR1 variants (c.1983 G>A, p.Trp661*; c.7025A>G, p.Asn2342Ser and c.2447 C>T, p.Pro816Leu) in a family with a suspected myopathy and associated malignant hyperthermia susceptibility. We used calcium release assays to functionally characterise these variants in a recombinant system.

METHODS

Site-directed mutagenesis was used to introduce each variant separately into the human RYR1 cDNA. HEK293-T cells were transfected with the recombinant constructs and calcium release assays were carried out using 4-chloro-m-cresol (4-CmC) as the RyR1 agonist to investigate the functional consequences of each variant.

RESULTS

RYR1 c.1983 G>A, p.Trp661* resulted in a non-functional channel, c.7025A>G, p.Asn2342Ser in a hypersensitive channel and c.2447 C>T, p.Pro816Leu in a hypersensitive channel at higher concentrations of 4-CmC.

CONCLUSIONS

The p.Trp661* RYR1 variant should be considered as a risk factor for myopathies. The p.Asn2342Ser RYR1 variant, when expressed as a compound heterozygote with a nonsense mutation on the second allele, is likely to result in MH-susceptibility. The role of the p.Pro816Leu variant in MH remains unclear.

Functional Characterization of C-terminal Ryanodine Receptor 1 Variants Associated with Central Core Disease or Malignant Hyperthermia

Background: Central core disease and malignant hyperthermia are human disorders of skeletal muscle resulting from aberrant Ca²⁺ handling. Most malignant hyperthermia and central core disease cases are associated with amino acid changes in the type 1 ryanodine receptor (RyR1), the skeletal muscle Ca²⁺-release channel. Malignant hyperthermia exhibits a gain-of-function phenotype, and central core disease results from loss of channel function. For a variant to be classified as pathogenic, functional studies must demonstrate a correlation with the pathophysiology of malignant hyperthermia or central core disease.

Objective: We assessed the pathogenicity of four C-terminal variants of the ryanodine receptor using functional analysis. The variants were identified in families affected by either malignant hyperthermia or central core disease.

Methods: Four variants were introduced separately into human cDNA encoding the skeletal muscle ryanodine receptor. Following transient expression in HEK-293T cells, functional studies were carried out using calcium release assays in response to an agonist. Two previously characterized variants and wild-type skeletal muscle ryanodine receptor were used as controls.

Results: The p.Met4640Ile variant associated with central core disease showed no difference in calcium release compared to wild-type. The p.Val4849Ile variant associated with malignant hyperthermia was more sensitive to agonist than wild-type but did not reach statistical significance and two variants (p.Phe4857Ser and p.Asp4918Asn) associated with central core disease were completely inactive.

Conclusions: The p.Val4849Ile variant should be considered a risk factor for malignant hyperthermia, while the p.Phe4857Ser and p.Asp4918Asn variants should be classified as pathogenic for central core disease.

Masseter muscle rigidity and the role of DNA analysis to confirm malignant hyperthermia susceptibility

Malignant hyperthermia (MH) is an uncommon, autosomal dominant disorder of skeletal muscle, triggered by inhalational anaesthetics or depolarizing muscle relaxants. Masseter muscle rigidity (MMR) can be regarded as potentially a preceding sign for an MH reaction. Susceptibility to MH can be determined by the in vitro contracture test (IVCT) or DNA analysis where a familial variant is known. Our aims were to review patients with MMR, where IVCT and DNA analysis had been undertaken, to determine if DNA analysis could be used as an initial screening tool for MH susceptibility, and, by reviewing standard monitored variables (SMVs), to determine if any clinical characteristics could be used to differentiate between MMR patients who are MH susceptible (MHS) and those who are not. Patients with MMR were identified from the Palmerston North Hospital MH Reactions Database. IVCT and DNA analysis results were documented. DNA testing was performed retrospectively in the majority of patients as many patients had presented before DNA analysis was available. Forty-one patients were analysed. Fourteen were DNA positive/IVCT positive and six DNA positive only (48% in total), seven were IVCT positive/DNA negative and 14 were IVCT normal. Increased creatine kinase (>18,000 units/L) was consistent with MH susceptibility. Severity of MMR was not linked to MH susceptibility. This study confirmed that DNA analysis can be used as a first-line test for MH susceptibility in patients presenting with MMR (consistent with European MH Group recommendations). Creatine kinase was the only SMV that was significantly different between MHS and MH normal individuals.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for the Use of Potent Volatile Anesthetic Agents and Succinylcholine in the Context of RYR1 or CACNA1S Genotypes

The identification in a patient of 1 of the 50 variants in the RYR1 or CACNA1S genes reviewed here should lead to a presumption of malignant hyperthermia susceptibility (MHS). MHS can lead to life-threatening reactions to potent volatile anesthetic agents or succinylcholine. We summarize evidence from the literature supporting this association and provide therapeutic recommendations for the use of these agents in patients with these RYR1 or CACNA1S variants (updates at https://cpicpgx.org/guidelines and www.pharmgkb.org).

Malignant Hyperthermia Susceptibility and Related Diseases

This review identifies disease states associated with malignant hyperthermia susceptibility based on genotypic and phenotypic findings, and a framework is established for clinicians to identify a potentially malignant hyperthermia–susceptible patient.

Administration of Anaesthetic Triggering Agents to Patients Tested Malignant Hyperthermia Normal and Their Relatives in New Zealand: An Update

Testing for malignant hyperthermia in New Zealand involves two tests—in vitro contracture testing of excised lateral quadriceps muscle and DNA analysis. In vitro contracture testing is regarded as the gold standard in malignant hyperthermia diagnosis but several publications have questioned the reliability of a normal result. Analysis of 479 anaesthetic records in 280 patients or their descendants throughout New Zealand who had tested negative for malignant hyperthermia, demonstrated there was no evidence of malignant hyperthermia episodes in this group who had been administered anaesthetic triggering agents. A wide range of anaesthetics were used over the study period. Analysis of each anaesthetic record was undertaken using the malignant hyperthermia grading scale which determines the likelihood that an anaesthetic event represents a malignant hyperthermia episode. Confirmation of the negative results was further supported by normal DNA analysis of patients in 48% of anaesthetics. There are advantages to using inhalational agents in certain situations and although demonstrating a zero risk of a malignant hyperthermia episode is not statistically possible, evidence in this large series suggests that the risk of an episode in these patients is extremely low and may be negligible. We suggest that anaesthetic triggering agents can be used safely in patients with normal in vitro contracture tests, and in their descendants.

Functional analysis of RYR1 variants linked to malignant hyperthermia

Malignant hyperthermia manifests as a rapid and sustained rise in temperature in response to pharmacological triggering agents, e.g. inhalational anesthetics and the muscle relaxant suxamethonium. Other clinical signs include an increase in end-tidal CO₂, increased O₂ consumption, as well as tachycardia, and if untreated a malignant hyperthermia episode can result in death. The metabolic changes are caused by dysregulation of skeletal muscle Ca²⁺ homeostasis, resulting from a defective ryanodine receptor Ca²⁺ channel, which resides in the sarcoplasmic reticulum and controls the flux of Ca²⁺ ions from intracellular stores to the cytoplasm. Most genetic variants associated with susceptibility to malignant hyperthermia occur in the RYR1 gene encoding the ryanodine receptor type 1. While malignant hyperthermia susceptibility can be diagnosed by in vitro contracture testing of skeletal muscle biopsy tissue, it is advantageous to use DNA testing. Currently only 35 of over 400 potential variants in RYR1 have been classed as functionally causative of malignant hyperthermia and thus can be used for DNA diagnostic tests. Here we describe functional analysis of 2 RYR1 variants (c. 7042_7044delCAG, p.ΔGlu2348 and c.641C>T, p.Thr214Met) that occur in the same malignant hyperthermia susceptible family. The p.Glu2348 deletion, causes hypersensitivity to ryanodine receptor agonists using in vitro analysis of cloned human RYR1 cDNA expressed in HEK293T cells, while the Thr214Met substitution, does not appear to significantly alter sensitivity to agonist in the same system. We suggest that the c. 7042_7044delCAG, p.ΔGlu2348 RYR1 variant could be added to the list of diagnostic mutations for susceptibility to malignant hyperthermia.

Functional characterisation of the R2452W ryanodine receptor variant associated with malignant hyperthermia susceptibility

Malignant hyperthermia (MH) is a pharmacogenetic disorder that manifests in susceptible individuals exposed to volatile anaesthetics. Over 400 variants in the ryanodine receptor 1 (RYR1) have been reported but relatively few have been definitively associated with susceptibility to MH. This is largely due to the technical challenges of demonstrating abnormal Ca(2+) release from the sarcoplasmic reticulum. This study focuses on the R2452W variant and its functional characterisation with the aim of classifying this variant as MH causative. HEK293 cells were transiently transfected with full-length human wildtype or R2452W mutant RYR1 cDNA. In addition, B-lymphoblastoid cells from blood and myoblasts propagated from in vitro contracture tests were extracted from patients positive for the R2452W variant. All cell lines generated were loaded with the ratiometric dye Fura-2 AM, stimulated with the RYR1-specific agonist 4-chloro-m-cresol and Ca(2+) release from the sarcoplasmic/endoplasmic reticulum was monitored by fluorescence emission. All cells expressing the RYR1 R2452W variant show a significantly higher Ca(2+) release in response to the agonist, 4-chloro-m-cresol, compared to cells expressing RYR1 WT. These results indicate that the R2452W variant results in a hypersensitive ryanodine receptor 1 and suggest that the R2452W variant in the ryanodine receptor 1 is likely to be causative of MH.

[Anesthetic malignant hyperthermia: what's new in 2012?]

Malignant hyperthermia (MH) is a pharmacogenetic disorder of anesthesia. Recent advances dealing with epidemiology of MH and the safe anesthetic course of MH susceptible patients are shortly presented here with a special insight into the preparation of modern anesthesia workstations, which they will share in operating room.

Sequence capture and massively parallel sequencing to detect mutations associated with malignant hyperthermia

BACKGROUND

Malignant hyperthermia (MH) is a potentially fatal pharmacogenetic disorder in which intracellular calcium homeostasis in the skeletal muscle of susceptible individuals is disrupted upon exposure to halogenated anaesthetics. While MH is linked to the ryanodine receptor (RYR1) on chromosome 19 and the α1S subunit of the voltage-dependent L-type calcium channel (CACNA1S) on chromosome 1, mutations have been found in only 50-70% of patients, and subsequently, there is a need for a more powerful screening tool.

METHODS

Genomic DNA capture and next-generation sequencing was used to screen 32 genes involved in excitation-contraction coupling, skeletal muscle calcium homeostasis, or immune response in two MH patients. Lymphoblastoid cell lines were used to functionally characterize candidate RYR1 mutations in one family.

RESULTS

Sequence analysis revealed two putative causative mutations in RYR1 in one patient. Segregation analysis and functional analysis support a causative role of the detected variants. The amount of Ca(2+) released after stimulation with 4-chloro-m-cresol from B lymphocytes of the MH-susceptible patients in the family was significantly greater compared with that of Ca(2+) released from cells of an MH-negative family member. In the other patient, no causative mutations were identified in the 32 genes screened.

CONCLUSIONS

In this study, we successfully demonstrate the use of genomic DNA capture and next-generation sequencing for identification of putative mutations causing MH. We also suggest that whole exome sequencing may be necessary to identify MH causing mutations in patients where no mutations in RYR1 and CACNA1S have been identified thus far.