Referral indications for malignant hyperthermia susceptibility diagnostics in patients without adverse anesthetic events in the era of next-generation sequencing

Pathogenicity assessment of seven RYR1 variants in patients with confirmed susceptibility to malignant hyperthermia in the Netherlands

BACKGROUND

Malignant hyperthermia (MH) susceptibility is associated with variants in RYR1, the gene encoding the skeletal muscle ryanodine receptor-1 (RyR1), in 70-75% of patients. Functional characterisation demonstrating an increased sensitivity to RyR1 agonists is necessary among other criteria for inclusion in the European Malignant Hyperthermia Group list of MH susceptibility diagnostic variants.

METHODS

Seven variants in the RYR1 gene, p.Glu342Lys, p.Leu2288Ser, p.Phe2340Leu, p.Arg2676Trp, p.Val3324Ala, p.Phe4076Leu, and p.Trp5020Cys, identified in MH-susceptible individuals were introduced into the cDNA for the human RYR1 gene. These variants were tested in cultured human embryonic kidney HEK293 cells for their effect on calcium release in response to the RyR1 agonist 4-chloro-m-cresol. Calcium release of each variant was compared with wild-type and benign and pathogenic controls. Each variant was subjected to curation using the European Malignant Hyperthermia Group scoring matrix and ClinGen RYR1 Variant Curation Expert Panel guidelines.

RESULTS

Six of seven RYR1 variants (p.Glu342Lys, p.Leu2288Ser, p.Phe2340Leu, p.Arg2676Trp, p.Val3324Ala, p.Phe4076Leu) showed hypersensitivity to 4-chloro-m-cresol compared with wild-type. The p.Trp5020Cys variant did not release calcium in response to 4-chloro-m-cresol. All variants had minor allele frequencies <0.1%. Rare exome variant ensemble learner scores of p.Glu342Lys, p.Leu2288Ser, p.Phe4076Leu, and p.Trp5020Cys were >0.85, supporting pathogenicity.

CONCLUSIONS

The variants p.Glu342Lys, p.Leu2288Ser p.Phe2340Leu, and p.Arg2676Trp are pathogenic or likely pathogenic for MH and can be used for presymptomatic testing for MH susceptibility. As current knowledge on the p.Val3324Ala, p.Phe4076Leu, and p.Trp5020Cys variants remains insufficient, they are still classified as variants of uncertain significance.

Myopathic manifestations across the adult lifespan of patients with malignant hyperthermia susceptibility: a narrative review

Malignant hyperthermia susceptibility (MHS) designates individuals at risk of developing a hypermetabolic reaction triggered by halogenated anaesthetics or the depolarising neuromuscular blocking agent suxamethonium. Over the past few decades, beyond the operating theatre, myopathic manifestations impacting daily life are increasingly recognised as a prevalent phenomenon in MHS patients. At the request of the European Malignant Hyperthermia Group, we reviewed the literature and gathered the opinion of experts to define MHS-related myopathy as a distinct phenotype expressed across the adult lifespan of MHS patients unrelated to anaesthetic exposure; this serves to raise awareness about non-anaesthetic manifestations, potential therapies, and management of MHS-related myopathy. We focused on the clinical presentation, biochemical and histopathological findings, and the impact on patient well-being. The spectrum of symptoms of MHS-related myopathy encompasses muscle cramps, stiffness, myalgias, rhabdomyolysis, and weakness, with a wide age range of onset mainly during adulthood. Histopathological analysis can reveal nonspecific abnormalities suggestive of RYR1 involvement, while metabolic profiling reflects altered energy metabolism in MHS muscle. Myopathic manifestations can significantly impact patient quality of life and lead to functional limitations and socio-economic burden. While currently available therapies can provide symptomatic relief, there is a need for further research into targeted treatments addressing the underlying pathophysiology. Counselling early after establishing the MHS diagnosis, followed by multidisciplinary management involving various medical specialties, is crucial to optimise patient care.

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

Malignant hyperthermia: Report on a successful rescue of a case with the highest temperature of 44.2°C

Malignant hyperthermia (MH) is an inherited skeletal muscle disorder caused primarily by a genetic mutation, usually in the calcium channel gene of the muscle. This mutation can lead to muscle hypersensitivity to volatile anesthetics (such as sevoflurane) and the depolarizing muscle relaxant succinylcholine, resulting in hyperthermia, muscle stiffness, metabolic disturbances, and other severe physiological reactions. This condition may prove fatal unless it is recognized in its early stages and treatment is administered promptly and aggressively. We report a 13-year-old adolescent who underwent laparoscopic appendectomy and developed MH after the use of inhalational anesthetics, manifested by unremitting hyperthermia with a maximum temperature of 44.2°C, muscle rigidity, tachycardia, hypercapnia; and malignant arrhythmias, cardiogenic shock, hyperkalemia, metabolic, and respiratory acidosis. After early and timely recognition, multidisciplinary management and administration of dantrolene, the case was successfully treated. Exome sequencing revealed a point mutation (amino acid change) on the RYR1 gene: c.12700G>C(p.Val4234Leu). Due to the lack of ready-made dantrolene in our hospital, the patient in this case received dantrolene treatment only 6 h after the first observation of high body temperature. We review the development of the disease and summarize the success of treatment and what can be done to improve the chances of saving the patient's life if dantrolene is not available in time.

Real Evidence and Misconceptions about Malignant Hyperthermia in Children: A Narrative Review

Malignant hyperthermia is a rare but life-threatening pharmacogenetic disorder triggered by exposure to specific anesthetic agents. Although this occurrence could affect virtually any patient during the perioperative time, the pediatric population is particularly vulnerable, and it has a five-fold higher incidence in children compared to adults. In the last few decades, synergistic efforts among leading anesthesiology, pediatrics, and neurology associations have produced new evidence concerning the diagnostic pathway, avoiding unnecessary testing and limiting false diagnoses. However, a personalized approach and an effective prevention policy focused on clearly recognizing the high-risk population, defining perioperative trigger-free hospitalization, and rapid activation of supportive therapy should be improved. Based on epidemiological data, many national scientific societies have produced consistent guidelines, but many misconceptions are common among physicians and healthcare workers. This review shall consider all these aspects and summarize the most recent updates.

Muscle Ultrasound Abnormalities in Individuals with RYR1-Related Malignant Hyperthermia Susceptibility

BACKGROUND

Variants in RYR1, the gene encoding the ryanodine receptor-1, can give rise to a wide spectrum of neuromuscular conditions. Muscle imaging abnormalities have been demonstrated in isolated cases of patients with a history of RYR1-related malignant hyperthermia (MH) susceptibility.

OBJECTIVE

To provide insights into the type and prevalence of muscle ultrasound abnormalities and muscle hypertrophy in patients carrying gain-of-function RYR1 variants associated with MH susceptibility and to contribute to delineating the wider phenotype, optimizing the diagnostic work-up and care for of MH susceptible patients.

METHODS

We performed a prospective cross-sectional observational muscle ultrasound study in patients with a history of RYR1-related MH susceptibility (n = 40). Study procedures included a standardized history of neuromuscular symptoms and a muscle ultrasound assessment. Muscle ultrasound images were analyzed using a quantitative and qualitative approach and compared to reference values and subsequently subjected to a screening protocol for neuromuscular disorders.

RESULTS

A total of 15 (38%) patients had an abnormal muscle ultrasound result, 4 (10%) had a borderline muscle ultrasound screening result, and 21 (53%) had a normal muscle ultrasound screening result. The proportion of symptomatic patients with an abnormal result (11 of 24; 46%) was not significantly higher compared to the proportion of asymptomatic patients with an abnormal ultrasound result (4 of 16; 25%) (P = 0.182). The mean z-scores of the biceps brachii (z = 1.45; P <  0.001), biceps femoris (z = 0.43; P = 0.002), deltoid (z = 0.31; P = 0.009), trapezius (z = 0.38; P = 0.010) and the sum of all muscles (z = 0.40; P <  0.001) were significantly higher compared to 0, indicating hypertrophy.

CONCLUSIONS

Patients with RYR1 variants resulting in MH susceptibility often have muscle ultrasound abnormalities. Frequently observed muscle ultrasound abnormalities include muscle hypertrophy and increased echogenicity.

European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders

BACKGROUND AND PURPOSE

Patients with neuromuscular conditions are at increased risk of suffering perioperative complications related to anaesthesia. There is currently little specific anaesthetic guidance concerning these patients. Here, we present the European Neuromuscular Centre (ENMC) consensus statement on anaesthesia in patients with neuromuscular disorders as formulated during the 259th ENMC Workshop on Anaesthesia in Neuromuscular Disorders.

METHODS

International experts in the field of (paediatric) anaesthesia, neurology, and genetics were invited to participate in the ENMC workshop. A literature search was conducted in PubMed and Embase, the main findings of which were disseminated to the participants and presented during the workshop. Depending on specific expertise, participants presented the existing evidence and their expert opinion concerning anaesthetic management in six specific groups of myopathies and neuromuscular junction disorders. The consensus statement was prepared according to the AGREE II (Appraisal of Guidelines for Research &amp; Evaluation) reporting checklist. The level of evidence has been adapted according to the SIGN (Scottish Intercollegiate Guidelines Network) grading system. The final consensus statement was subjected to a modified Delphi process.

RESULTS

A set of general recommendations valid for the anaesthetic management of patients with neuromuscular disorders in general have been formulated. Specific recommendations were formulated for (i) neuromuscular junction disorders, (ii) muscle channelopathies (nondystrophic myotonia and periodic paralysis), (iii) myotonic dystrophy (types 1 and 2), (iv) muscular dystrophies, (v) congenital myopathies and congenital dystrophies, and (vi) mitochondrial and metabolic myopathies.

CONCLUSIONS

This ENMC consensus statement summarizes the most important considerations for planning and performing anaesthesia in patients with neuromuscular disorders.

Risk of malignant hyperthermia in patients carrying a variant in the skeletal muscle ryanodine receptor 1 gene

Malignant hyperthermia is a life-threatening disorder, which can be prevented by avoiding certain anesthetic agents. Pathogenic variants in the skeletal muscle ryanodine receptor 1-gene are linked to malignant hyperthermia. We retrospectively studied 15 patients who presented to our clinic with symptoms of muscle dysfunction (weakness, myalgia or cramps) and were later found to have a variant in the skeletal muscle ryanodine receptor 1-gene. Symptoms, creatine kinase levels, electromyography, muscle biopsy and in vitro contracture test results were reviewed. Six out of the eleven patients, with a variant of unknown significance in the skeletal muscle ryanodine receptor 1-gene, had a positive in vitro contracture test, indicating malignant hyperthermia susceptibility. In one patient, with two variants of unknown significance, both variants were required to express the malignant hyperthermia-susceptibility trait. Neurologists should consider screening the skeletal muscle ryanodine receptor 1-gene in patients with myalgia or cramps, even when few to no abnormalities on ancillary testing.

Neuromuscular symptoms in patients with RYR1-related malignant hyperthermia and rhabdomyolysis

Malignant hyperthermia and exertional rhabdomyolysis have conventionally been considered episodic phenotypes that occur in otherwise healthy individuals in response to an external trigger. However, recent studies have demonstrated a clinical and histopathological continuum between patients with a history of malignant hyperthermia susceptibility and/or exertional rhabdomyolysis and RYR1-related congenital myopathies. We hypothesize that patients with a history of RYR1-related exertional rhabdomyolysis or malignant hyperthermia susceptibility do have permanent neuromuscular symptoms between malignant hyperthermia or exertional rhabdomyolysis episodes. We performed a prospective cross-sectional observational clinical study of neuromuscular features in patients with a history of RYR1-related exertional rhabdomyolysis and/or malignant hyperthermia susceptibility (n = 40) compared with healthy controls (n = 80). Patients with an RYR1-related congenital myopathy, manifesting as muscle weakness preceding other symptoms as well as other (neuromuscular) diseases resulting in muscle weakness were excluded. Study procedures included a standardized history of neuromuscular symptoms, a review of all relevant ancillary diagnostic tests performed up to the point of inclusion and a comprehensive, standardized neuromuscular assessment. Results of the standardized neuromuscular history were compared with healthy controls. Results of the neuromuscular assessment were compared with validated reference values. The proportion of patients suffering from cramps (P < 0.001), myalgia (P < 0.001) and exertional myalgia (P < 0.001) was higher compared with healthy controls. Healthcare professionals were consulted because of apparent neuromuscular symptoms by 17/40 (42.5%) patients and 7/80 (8.8%) healthy controls (P < 0.001). Apart from elevated creatine kinase levels in 19/40 (47.5%) patients and mild abnormalities on muscle biopsies identified in 13/16 (81.3%), ancillary investigations were normal in most patients. The Medical Research Council sum score, spirometry and results of functional measurements were also mostly normal. Three of 40 patients (7.5%) suffered from late-onset muscle weakness, most prominent in the proximal lower extremity muscles. Patients with RYR1 variants resulting in malignant hyperthermia susceptibility and/or exertional rhabdomyolysis frequently report additional neuromuscular symptoms such as myalgia and muscle cramps compared with healthy controls. These symptoms result in frequent consultation of healthcare professionals and sometimes in unnecessary invasive diagnostic procedures. Most patients do have normal strength at a younger age but may develop muscle weakness later in life.

Malignant Hyperthermia in PICU—From Diagnosis to Treatment in the Light of Up-to-Date Knowledge

Malignant Hyperthermia (MH) is a rare, hereditary, life-threatening disease triggered by volatile anesthetics and succinylcholine. Rarely, MH can occur after non-pharmacological triggers too. MH was detected more often in children and young adults, which makes this topic very important for every pediatric specialist, both anesthesiologists and intensivists. MH crisis is a life-threatening severe hypermetabolic whole-body reaction. Triggers of MH are used in pediatric intensive care unit (PICU) as well, volatile anesthetics in difficult sedation, status asthmaticus or epilepticus, and succinylcholine still sometimes in airway management. Recrudescence or delayed onset of MH crisis hours after anesthesia was previously described. MH can also be a cause of rhabdomyolysis and hyperpyrexia in the PICU. In addition, patients with neuromuscular diseases are often admitted to PICU and they might be at risk for MH. The most typical symptoms of MH are hypercapnia, tachycardia, hyperthermia, and muscle rigidity. Thinking of the MH as the possible cause of deterioration of a patient’s clinical condition is the key to early diagnosis and treatment. The sooner the correct treatment is commenced, the better patient´s outcome. This narrative review article aims to summarize current knowledge and guidelines about recognition, treatment, and further management of MH in PICU.