Genetics of Malignant Hyperthermia: A Brief Update

Novel ryanodine receptor 1 (RYR1) missense gene variants in two pet dogs with fatal malignant hyperthermia identified by next-generation sequencing

OBJECTIVE

Evaluate a precision medicine approach to confirm a tentative diagnosis of fatal malignant hyperthermia (MH) in isoflurane-anesthetized pet dogs by identifying novel risk variants in known MH susceptibility genes.

STUDY DESIGN

Retrospective case series.

ANIMALS

A male Pit Bull mix aged 7 years (case #1), a male Golden Retriever aged 12 months (case #2) and the dam and sire of case #2.

METHODS

Available case histories and medical records were reviewed. Missense variants in MH susceptibility genes RYR-1, CACNA1S and STAC3 (case #2 only) were identified by next-generation sequencing of DNA from each case and the parents of case #2 with confirmation by Sanger sequencing. The pathogenicity of variants was evaluated by multiple in silico approaches.

RESULTS

Both cases demonstrated clinical signs during isoflurane anesthesia consistent with volatile anesthetic-induced MH, including tachypnea, tachycardia, severe hyperthermia and muscle rigidity. Despite whole body cooling and other treatments, both dogs died after cardiac arrest within 15 minutes of detecting hyperthermia. Gene sequencing identified novel missense RYR-1 variants in case #1 (p.Gly2375Arg) and case #2 (p.Pro152Leu). Both variants were likely pathogenic based on multiple criteria, including gene location, amino acid alteration and population allele frequency. The case #1 variant was identical to a known human diagnostic MH variant (p.Gly2375Arg). Neither parent of case #2 had the case #2 variant, indicating this variant was not inherited, but arose de novo in a germ cell of either parent or early in embryogenesis. Whole genome sequence analysis confirmed parentage. Two missense variants were identified in CACNA1S. Both variants were considered nonpathogenic. No variants were identified in STAC3.

CONCLUSIONS AND CLINICAL RELEVANCE

Like humans, MH susceptibility in dogs is associated with different rare variants located in pathogenic hotspots in the RYR-1 gene. Next-generation sequencing is a useful tool to assist in the definitive diagnosis of MH in dogs.

Evaluation of Malignant Hyperthermia Features in Patients with Pathogenic or Likely Pathogenic RYR1 Variants Disclosed through a Population Genomic Screening Program

BACKGROUND

Malignant hyperthermia (MH) susceptibility is a heritable musculoskeletal disorder that can present as a potentially fatal hypermetabolic response to triggering anesthesia agents. Genomic screening for variants in MH-associated genes RYR1 and CACNA1S provides an opportunity to prevent morbidity and mortality. There are limited outcomes data from disclosing variants in RYR1, the most common MH susceptibility gene, in unselected populations. The authors sought to identify the rate of MH features or fulminant episodes after triggering agent exposure in an unselected population undergoing genomic screening including actionable RYR1 variants.

METHODS

The MyCode Community Health Initiative by Geisinger (USA) is an electronic health record-linked biobank that discloses pathogenic and likely pathogenic variants in clinically actionable genes to patient-participants. Available electronic anesthesia and ambulatory records for participants with actionable RYR1 results returned through December 2020 were evaluated for pertinent findings via double-coded chart reviews and reconciliation. Descriptive statistics for observed phenotypes were calculated.

RESULTS

One hundred fifty-two participants had an actionable RYR1 variant disclosed during the study period. None had previous documented genetic testing for MH susceptibility; one had previous contracture testing diagnosing MH susceptibility. Sixty-eight participants (44.7%) had anesthesia records documenting triggering agent exposure during at least one procedure. None received dantrolene treatment or had documented muscle rigidity, myoglobinuria, hyperkalemia, elevated creatine kinase, severe myalgia, or tea-colored urine. Of 120 possibly MH-related findings (postoperative intensive care unit admissions, hyperthermia, arterial blood gas evaluation, hypercapnia, or tachycardia), 112 (93.3%) were deemed unlikely to be MH events; 8 (6.7%) had insufficient records to determine etiology.

CONCLUSIONS

Results demonstrate a low frequency of classic intraanesthetic hypermetabolic phenotypes in an unselected population with actionable RYR1 variants. Further research on the actionability of screening for MH susceptibility in unselected populations, including economic impact, predictors of MH episodes, and expanded clinical phenotypes, is necessary.

EDITOR’S PERSPECTIVE

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