Malignant Hyperthermia Susceptibility and Related Diseases

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.

Anesthetic Management of Two Patients With PHARC Syndrome: Case Report

PHARC syndrome (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts) is a rare autosomal recessive disease, caused by genetic mutation of the ABHD12 gene. This syndrome is still not well known and can be misdiagnosed, especially in the early stages, as it can be easily confused with other neurodegenerative diseases. We present the first description of the anesthetic management of 2 siblings with PHARC syndrome who underwent unilateral cochlear implantation.

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.

Functional benefit of CRISPR-Cas9-induced allele deletion for RYR1 dominant mutation

More than 700 pathogenic or probably pathogenic variations have been identified in the RYR1 gene causing various myopathies collectively known as "RYR1-related myopathies." There is no treatment for these myopathies, and gene therapy stands out as one of the most promising approaches. In the context of a dominant form of central core disease due to a RYR1 mutation, we aimed at showing the functional benefit of inactivating specifically the mutated RYR1 allele by guiding CRISPR-Cas9 cleavages onto frequent single-nucleotide polymorphisms (SNPs) segregating on the same chromosome. Whole-genome sequencing was used to pinpoint SNPs localized on the mutant RYR1 allele and identified specific CRISPR-Cas9 guide RNAs. Lentiviruses encoding these guide RNAs and the SpCas9 nuclease were used to transduce immortalized patient myoblasts, inducing the specific deletion of the mutant RYR1 allele. The efficiency of the deletion was assessed at DNA and RNA levels, and at the functional level after monitoring calcium release induced by the stimulation of the RyR1-channel. This study provides in cellulo proof of concept regarding the benefits of mutant RYR1 allele deletion, in the case of a dominant RYR1 mutation, from both a molecular and functional perspective, and could apply potentially to 20% of all patients with a RYR1 mutation.

Artificial intelligence approaches to the volumetric quantification of glycogen granules in EM images of human tissue

Skeletal muscle, the major processor of dietary glucose, stores it in myriad glycogen granules. Their numbers vary with cellular location and physiological and pathophysiological states. AI models were developed to derive granular glycogen content from electron-microscopic images of human muscle. Two UNet-type semantic segmentation models were built: "Locations" classified pixels as belonging to different regions in the cell; "Granules" identified pixels within granules. From their joint output, a pixel fraction pf was calculated for images from patients positive (MHS) or negative (MHN) to a test for malignant hyperthermia susceptibility. pf was used to derive vf, the volume fraction occupied by granules. The relationship vf (pf) was derived from a simulation of volumes ("baskets") containing virtual granules at realistic concentrations. The simulated granules had diameters matching the real ones, which were measured by adapting a utility devised for calcium sparks. Applying this relationship to the pf measured in images, vf was calculated for every region and patient, and from them a glycogen concentration. The intermyofibrillar spaces and the sarcomeric I band had the highest granular content. The measured glycogen concentration was low enough to allow for a substantial presence of non-granular glycogen. The MHS samples had an approximately threefold lower concentration (significant in a hierarchical test), consistent with earlier evidence of diminished glucose processing in MHS. The AI models and the approach to infer three-dimensional magnitudes from two-dimensional images should be adaptable to other tasks on a variety of images from patients and animal models and different disease conditions.

Burning Question: How Does Our Brain Process Positive and Negative Cues Associated with Thermosensation?

Whether it is the dramatic suffocating sensation from a heat wave in the summer or the positive reinforcement arising from a hot drink on a cold day; we can certainly agree that our thermal environment underlies our daily rhythms of sensation. Extensive research has focused on deciphering the central circuits responsible for conveying the impact of thermogenesis on mammalian behavior. Here, we revise the recent literature responsible for defining the behavioral correlates that arise from thermogenic fluctuations in mammals. We transition from the physiological significance of thermosensation to the circuitry responsible for the autonomic or behavioral responses associated with it. Subsequently, we delve into the positive and negative valence encoded by thermoregulatory processes. Importantly, we emphasize the crucial junctures where reward, pain, and thermoregulation intersect, unveiling a complex interplay within these neural circuits. Finally, we briefly outline fundamental questions that are pending to be addressed in the field. Fully deciphering the thermoregulatory circuitry in mammals will have far-reaching medical implications. For instance, it may lead to the identification of novel targets to overcome thermal pain or allow the maintenance of our core temperature in prolonged surgeries.

Ventilatory failure in chronic neuromuscular disease

Patients with neuromuscular diseases (NMD) can present to the neurologist with symptoms and signs of respiratory failure, either acutely or as an insidious process in the outpatient setting. Since the advent of non-invasive ventilation, the outcomes of patients with ventilatory failure due to NMD have dramatically improved. However, the natural history of different NMDs requires a nuanced approach to respiratory investigation and management. Respiratory failure dictates the prognosis of many NMDs and timing the most appropriate investigation and referral to ventilation services is crucial in optimising care.

Application of Advanced Technologies-Nanotechnology, Genomics Technology, and 3D Printing Technology-In Precision Anesthesia: A Comprehensive Narrative Review

There has been increasing interest and rapid developments in precision medicine, which is a new medical concept and model based on individualized medicine with the joint application of genomics, bioinformatics engineering, and big data science. By applying numerous emerging medical frontier technologies, precision medicine could allow individualized and precise treatment for specific diseases and patients. This article reviews the application and progress of advanced technologies in the anesthesiology field, in which nanotechnology and genomics can provide more personalized anesthesia protocols, while 3D printing can yield more patient-friendly anesthesia supplies and technical training materials to improve the accuracy and efficiency of decision-making in anesthesiology. The objective of this manuscript is to analyze the recent scientific evidence on the application of nanotechnology in anesthesiology. It specifically focuses on nanomedicine, precision medicine, and clinical anesthesia. In addition, it also includes genomics and 3D printing. By studying the current research and advancements in these advanced technologies, this review aims to provide a deeper understanding of the potential impact of these advanced technologies on improving anesthesia techniques, personalized pain management, and advancing precision medicine in the field of anesthesia.

A case report of Andersen-Tawil syndrome misdiagnosed with myodystrophy

Andersen-Tawil syndrome (ATS) is a rare periodic paralysis caused by the KCNJ2 gene mutation. Here, we report on an ATS patient misdiagnosed with myodystrophy. A 66-year-old man presented with a 60-year history of episodic weakness in the proximal muscles of the upper and lower limbs. The man has been diagnosed with muscle pathology and has undergone genetic examinations in many hospitals since childhood. We conducted a correct diagnosis in combination with the patient's history, electrical physiology, and genetic analysis and identified a heterozygous KCNJ2 gene variant (c.220A > G; p.T74A). Patients with ATS can develop permanent myasthenia characterized by chronic progressive myopathy. ATS patients should also pay special attention to the risks of anesthesia in surgery, including malignant hyperthermia (MH), muscle spasms affecting tracheal intubation or ventilation, and ventilator weakness. Early diagnosis and therapy could help delay the onset of myasthenia and prevent risks associated with anesthesia accidents.

Rhabdomyosarcoma Associated with Core Myopathy/Malignant Hyperthermia: Combined Effect of Germline Variants in RYR1 and ASPSCR1 May Play a Role

Rhabdomyosarcomas have been described in association with thyroid disease, dermatomyositis, Duchenne muscular dystrophy, and in muscular dystrophy models but not in patients with ryanodine receptor-1 gene (RYR1) pathogenic variants. We described here an 18-year-old male who reported a cervical nodule. Magnetic resonance images revealed a mass in the ethmoidal sinus corresponding to rhabdomyosarcoma. As his father died from malignant hyperthermia (MH), an in vitro contracture test was conducted and was positive for MH susceptibility. Muscle histopathological analysis in the biopsy showed the presence of cores. Molecular analysis using NGS sequencing identified germline variants in the RYR1 and ASPSCR1 (alveolar soft part sarcoma) genes. This report expands the spectrum of diseases associated with rhabdomyosarcomas and a possible differential diagnosis of soft tissue tumors in patients with RYR1 variants.

Patient suspected susceptibility to malignant hyperthermia: impact of the disease

INTRODUCTION

Malignant Hyperthermia (MH) is an inherited hypermetabolic syndrome triggered by exposure to halogenated anesthetics/succinylcholine. The lack of knowledge regarding this condition might be associated with the rare occurrence of MH reaction and symptoms.

METHODS

This observational study evaluated 68 patients from 48 families with confirmed or suspected MH susceptibility due to medical history of MH reaction or idiopathic increase of creatine kinase or MH-related myopathies. Participants were assessed by a standardized questionnaire and submitted to physical/neurological examination to assess the characteristics of patients with MH, their knowledge about the disease, and the impact suspected MH had on their daily lives.

RESULTS

Suspected MH impacted the daily life of 50% of patients, creating difficulties in performing surgical/clinical/dental treatment and problems related to their family life/working/practicing sports. The questionnaire on MH revealed a correct answer score of 62.1 ± 20.8 (mean ± standard deviation) on a scale 0 to 100. Abnormal physical/neurological examination findings were detected in 92.6% of susceptible patients.

CONCLUSIONS

Suspected MH had impacted the daily lives of most patients, with patients reporting problems even before MH investigation with IVCT. Patients showed a moderate level of knowledge about MH, suggesting the need to implement continuing education programs. MH susceptible patients require regular follow-up by a health team to detect abnormalities during physical and neurological examination.

Fatigue, depression, and physical activity in patients with malignant hyperthermia: a cross-sectional observational study

BACKGROUND

Malignant Hyperthermia (MH) is a pharmacogenetic disorder triggered by halogenated anesthesia agents/succinylcholine and characterized by hypermetabolism crisis during anesthesia, but also by day-to-day symptoms, such as exercise intolerance, that may alert the health professional.

OBJECTIVE

The study aimed to analyze the incidence of fatigue in MH susceptible patients and the variables that can impact perception of fatigue, such as the level of routine physical activity and depression.

METHODS

A cross-sectional observational study was carried out with three groups ... 22 patients susceptible to MH (positive in vitro muscle contracture test), 13 non-susceptible to MH (negative in vitro muscle contracture test) and 22 controls (no history of MH). Groups were assessed by a demographic/clinical questionnaire, a fatigue severity scale (intensity, specific situations, psychological consequences, rest/sleep response), and the Beck depression scale. Subgroups were re-assessed with the Baecke habitual physical exercise questionnaire (occupational physical activity, leisure physical exercise, leisure/locomotion physical activity).

RESULTS

There were no significant differences among the three groups regarding fatigue intensity, fatigue related to specific situations, psychological consequences of fatigue, fatigue response to resting/sleeping, depression, number of active/sedentary participants, and the mean time and characteristics of habitual physical activity. Nevertheless, unlike the control sub-group, the physically active MH-susceptible subgroup had a higher fatigue response to resting/sleeping than the sedentary MH susceptible subgroup (respectively, 5.9.ß...ß1.9 vs. 3.9.ß...ß2, t-test unpaired, p.ß<.ß0.05).

CONCLUSION

We did not detect subjective fatigue in MH susceptible patients, although we reported protracted recovery after physical activity, which may alert us to further investigation requirements.

Muscle calcium stress cleaves junctophilin1, unleashing a gene regulatory program predicted to correct glucose dysregulation

Calcium ion movements between cellular stores and the cytosol govern muscle contraction, the most energy-consuming function in mammals, which confers skeletal myofibers a pivotal role in glycemia regulation. Chronic myoplasmic calcium elevation ("calcium stress"), found in malignant hyperthermia-susceptible (MHS) patients and multiple myopathies, has been suggested to underlie the progression from hyperglycemia to insulin resistance. What drives such progression remains elusive. We find that muscle cells derived from MHS patients have increased content of an activated fragment of GSK3β - a specialized kinase that inhibits glycogen synthase, impairing glucose utilization and delineating a path to hyperglycemia. We also find decreased content of junctophilin1, an essential structural protein that colocalizes in the couplon with the voltage-sensing CaV1.1, the calcium channel RyR1 and calpain1, accompanied by an increase in a 44 kDa junctophilin1 fragment (JPh44) that moves into nuclei. We trace these changes to activated proteolysis by calpain1, secondary to increased myoplasmic calcium. We demonstrate that a JPh44-like construct induces transcriptional changes predictive of increased glucose utilization in myoblasts, including less transcription and translation of GSK3β and decreased transcription of proteins that reduce utilization of glucose. These effects reveal a stress-adaptive response, mediated by the novel regulator of transcription JPh44.

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.

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.

Management of patients susceptible to malignant hyperthermia: A surgeon's perspective

OBJECTIVES

Malignant hyperthermia (MH) susceptibility caries broad implications for the care of pediatric surgical patients. While precautions must often be taken for only a vague family history, two options exist to assess MH-susceptibility. We evaluate the use of MH precautions and susceptibility testing at a freestanding children's hospital.

METHODS

This single institution retrospective cohort study identified patients of any age who received general anesthetics utilizing MH precautions over a five-year period. The electronic medical record was further queried for patients diagnosed with MH. The indication for MH precautions and uses of susceptibility testing are assessed. Secondary outcomes included a diagnosis of bona fide MH.

RESULTS

A total of 125 patients received 174 anesthetics with MH precautions at a mean age of 114 months (0-363 months). Otolaryngology was the procedural service most frequently involved in the care of the cohort (n = 45; 26%). A reported personal or family history of MH (n = 102; 59%) was the most common indication for precautions, followed by muscular dystrophy (n = 29; 17%). No MH events occurred in the cohort and further review of ICD-9 and -10 diagnosis codes found no MH diagnoses. No study subjects received muscle biopsy and contracture testing and only 5 (4%) underwent genetic testing for genomic variants known to cause MH susceptibility. A case example is given to highlight the implications of a reported MH history.

CONCLUSION

Otolaryngologists should maintain a familiarity with the precautions necessary to manage patients at risk for MH and MH-like reactions. Without an accessible test to rule out susceptibility, surgeons must rely on a careful history to appropriately utilize precautions. An inappropriate label of "MH-susceptible" may result in decreased access to care and treatment delays.

Impact of a digital manual for guidance on malignant hyperthermia: patient education

Background

Malignant hyperthermia (MH) is a rare, hereditary disease with a hypermetabolic response to volatile anesthetics/succinylcholine. Susceptible patients face difficulties due to a lack of knowledge about MH. As informational materials could increase knowledge and adherence to prevention/therapy, digital information about rare diseases validated for patients is needed. Our objective was to evaluate the following: (1) the impact of digital manuals on the knowledge/quality of life of MH patients and (2) access to MH services.

Materials and methods

Fifty MH-susceptible patients filled out a virtual questionnaire twice (demographic/economic/clinical data, MH knowledge and impact on daily life, and SF-36 quality of life). Test groups 1 (n = 17) and 2 (n = 16) were evaluated 30 and 180 days after receiving a digital manual, and the control group (n = 17; without manual) was evaluated after 180 days. We collected the MH service data about the number of contacts.

Results

Twenty-four (48%) patients reported problems in personal/professional life, sports, clinical/surgical/dental treatments, and military service, in addition to concerns about emergency care and complaints of sequelae. The percentage of correct answers in the second MH knowledge questionnaire increased for test group 2 (62% vs. 74.1%; unpaired t test, p < 0.01), was significantly greater in test groups 1 (68.1%) and 2 (74.1%) than in the control group (56.5%; Kruskal–Wallis, p < 0.05), and correlated with more time studying the manual and reports of MH-related problems (multiple regression, p < 0.05).

Conclusions

The digital manual improved patients’ MH knowledge. Online contacts with the MH service increased, allowing greater information dissemination. As informational materials could increase knowledge/adherence to prevention/therapy, digital information about MH validated for patients should be implemented.

Creation and Implementation of a Preoperative Malignant Hyperthermia Screening Tool

BACKGROUND

Malignant hyperthermia (MH) is a potentially lethal pharmacogenetic disorder triggered by certain anesthetic agents. There is currently no standardized preoperative screening tool utilized to identify MH-susceptible individuals.

LOCAL PROBLEM

This quality improvement (QI) project aimed to enhance preoperative screening for MH susceptibility (MHS) by implementing an evidence-based screening tool for surgical patients at 2 sites.

METHODS

This prospective descriptive QI project evaluated the success of implementing an MHS screening tool preoperatively and its impact on the anesthesia plan.

INTERVENTIONS

Anesthesia professionals included the screening tool in their preoperative interview for surgical patients so that positively screened patients could receive MH prevention measures.

RESULTS

A total of 95 patients at site A and 234 patients at site B were screened using the MH tool, a cumulative total of 21 patients were positively screened, and 1 anesthetic plan was altered.

CONCLUSIONS

This MHS screening tool has the potential to prevent MH episodes when used consistently by staff.

Variants in ASPH cause exertional heat illness and are associated with malignant hyperthermia susceptibility

Exertional heat illness (EHI) and malignant hyperthermia (MH) are life threatening conditions associated with muscle breakdown in the setting of triggering factors including volatile anesthetics, exercise, and high environmental temperature. To identify new genetic variants that predispose to EHI and/or MH, we performed genomic sequencing on a cohort with EHI/MH and/or abnormal caffeine-halothane contracture test. In five individuals, we identified rare, pathogenic heterozygous variants in ASPH, a gene encoding junctin, a regulator of excitation-contraction coupling. We validated the pathogenicity of these variants using orthogonal pre-clinical models, CRISPR-edited C2C12 myotubes and transgenic zebrafish. In total, we demonstrate that ASPH variants represent a new cause of EHI and MH susceptibility.

Mapping the current evidence on the anesthetic management of adult patients with neuromuscular disorders-a scoping review

PURPOSE

Patients with neuromuscular disorders (NMDs) are at increased risk of perioperative complications. The objective of this scoping review was to examine emerging evidence from published studies, case reports, and review articles on anesthetic management of patients with NMDs, following the methodological frame for scoping reviews.

SOURCES

We searched PubMed and EMBASE for articles published between 1 January 2000 and 14 July 2021.

PRINCIPAL FINDINGS

Three prospective and 21 retrospective studies on altered pharmacokinetics and pharmacodynamics of neuromuscular blocking agents (NMBA) in NMD patients were included. Furthermore, 168 case reports/series reporting 212 anesthetics in 197 patients were included. These studies showed that preanesthetic neuromuscular monitoring can be used for precise NMBA dosing in myasthenia gravis patients. Sugammadex was associated with fewer postoperative myasthenic crises. Perioperative complications were not associated with specific anesthetic agents. Case reports/series showed that in 32% (67/212) of anesthetics, at least one complication was reported. Unexpected intensive care unit admission was a frequently reported complication. Patients with a complicated disease course may have had a higher use of succinylcholine (unadjusted relative risk, 0.13; 95% confidence interval [CI], 0.20 to 0.86) and volatile anesthetics (adjusted odds ratio [OR], 0.38; 95% CI, 0.20 to 0.73; P = 0.004).

CONCLUSION

Evidence on the anesthetic management and perioperative complications of patients with NMDs is mainly based on small retrospective studies and case reports. Further clinical trials or large retrospective studies are required to investigate the choice of safe anesthetic agents. Main areas of interest are the potential benefits of neuromuscular monitoring and sugammadex and the risks possibly associated with volatile anesthetics and succinylcholine.

Expanding the clinical-pathological and genetic spectrum of RYR1-related congenital myopathies with cores and minicores: an Italian population study

Mutations in the RYR1 gene, encoding ryanodine receptor 1 (RyR1), are a well-known cause of Central Core Disease (CCD) and Multi-minicore Disease (MmD). We screened a cohort of 153 patients carrying an histopathological diagnosis of core myopathy (cores and minicores) for RYR1 mutation. At least one RYR1 mutation was identified in 69 of them and these patients were further studied. Clinical and histopathological features were collected. Clinical phenotype was highly heterogeneous ranging from asymptomatic or paucisymptomatic hyperCKemia to severe muscle weakness and skeletal deformity with loss of ambulation. Sixty-eight RYR1 mutations, generally missense, were identified, of which 16 were novel. The combined analysis of the clinical presentation, disease progression and the structural bioinformatic analyses of RYR1 allowed to associate some phenotypes to mutations in specific domains. In addition, this study highlighted the structural bioinformatics potential in the prediction of the pathogenicity of RYR1 mutations. Further improvement in the comprehension of genotype-phenotype relationship of core myopathies can be expected in the next future: the actual lack of the human RyR1 crystal structure paired with the presence of large intrinsically disordered regions in RyR1, and the frequent presence of more than one RYR1 mutation in core myopathy patients, require designing novel investigation strategies to completely address RyR1 mutation effect.

Variant landscape of the RYR1 gene based on whole genome sequencing of the Singaporean population

The RYR1 gene codes for a ryanodine receptor which is a calcium release channel in the skeletal muscle sarcoplasmic reticulum. It is associated with Malignant Hyperthermia (MH) and congenital myopathies including Central Core Disease (CCD), Multiminicore Disease (MMD) and Congenital Fibre-Type Disproportion (CFTD). There is currently little information on the epidemiology of RYR1 variants in Asians. Our study aims to describe the RYR1 variant landscape in a Singapore cohort unselected for RYR1-associated conditions. Data was retrieved from the SG10K pilot project, where whole genome sequencing was performed on volunteers unselected and undetermined for RYR1-associated conditions. Variants were classified based on pathogenicity using databases ClinVar and InterVar. Allele frequencies of pathogenic variants were compared between Chinese, Indians and Malays. Using databases ExAC, GnomAD and GenomeAsia 100k study, we further compared local allele frequencies to those in Europe, America and Asia. Data was analysed using R Commander. Significant P value was set at p < 0.05. Majority of the RYR1 variants were missense mutations. We identified four pathogenic and four likely pathogenic RYR1 variants. All were related to the aforementioned RYR1-associated conditions. There were 6 carriers of RYR1 pathogenic variants amongst 4810 individuals, corresponding to an allele frequency of 0.06%. The prevalence of pathogenic variants was the highest amongst Indians (4 in 1127 individuals) (p = 0.030). Majority of pathogenic and likely pathogenic mutations were missense and located in mutational hotspots. These variants also occurred at higher frequencies in Asians than globally. This study describes the variant landscape of the RYR1 gene in Singapore. This knowledge will facilitate genetic screening for RYR1-related conditions.

Anesthesia in a Patient with Potocki-Lupski Syndrome

Introduction

Potocki–Lupski syndrome (PTLS) is a rare disease caused by the duplication of a small segment of chromosome 17 (17p11.2). The clinical presentation of this syndrome is quite variable and includes hypotonia, failure to thrive, oropharyngeal dysphagia, developmental delay, and behavioral abnormalities. In addition, congenital heart disease, sleep apnea, and mildly dysmorphic features are common and should be considered during anesthetic management. However, because of the rarity and newness of the syndrome, there are few reports on the anesthetic care of patients with PTLS. Case Report. We report a case of a 4-year-old girl diagnosed with this syndrome who underwent general anesthesia for exotropia surgery. The patient exhibited micrognathia; a mild decrease in muscle tone; and a developmental delay in motor, speech, and cognition. She had a history of swallowing incoordination and gastroesophageal reflux. No abnormalities were found on a preoperative echocardiography. A videolaryngoscope was used for tracheal intubation, and the state of neuromuscular blockade was monitored in addition to standard monitoring. Anesthesia was maintained with sevoflurane and remifentanil. The patient recovered without any adverse events.

Conclusion

As PTLS patients may have several malformations, preanesthetic evaluation is important. Preoperative echocardiography and cardiologic consultations are required. It is desirable to prepare for the risk of difficult airway and pulmonary aspiration. Postoperatively, close monitoring is needed to prevent airway compromise.

Challenges in Obstetric Anesthesia in a Parturient With Native American Myopathy: A Case Report

Native American Myopathy (NAM) is an inherited, malignant hyperthermia-susceptible myopathy associated with abnormal craniofacial development and neuromuscular scoliosis. There is scant NAM anesthetic literature and, to our knowledge, no existing publications describing the anesthetic management of a NAM parturient. The constellation of symptoms of NAM in the parturient presents a number of challenges to the obstetric anesthesiologist, including difficult airway associated with craniofacial abnormalities and pregnancy, malignant hyperthermia susceptibility, and possible difficult neuraxial block. In this report, we present the anesthetic management of a parturient with NAM and previous extensive posterior spinal fusion undergoing cesarean delivery under general anesthesia.

A case report of malignant hyperthermia in a patient with myotonic dystrophy type I: A CARE-compliant article

RATIONALE

Several hereditary myopathies that can predispose to malignant hyperthermia (MH) are reported. However, the risk of MH in myotonic dystrophy type I (DM1) has been suggested equal to general population, although the evidence is limited to only a few case reports.

PATIENT CONCERNS

We encountered a rare case of MH during anesthesia induction with sevoflurane in a male adolescent with previously undiagnosed DM1.

DIAGNOSES

After the event, genetic testing revealed the presence of a previously unknown heterozygous missense mutation in ryanodine receptor 1 (RYR1) associated with MH (c.6898T > C; p.ser2300Pro). Concomitantly, the patient was diagnosed with DM1 with abnormal cytosine-thymine-guanine triplet expansion in the DMPK gene.

INTERVENTIONS

Dantrolene was administered to treat the hypermetabolic manifestations in 20 minutes after the identification of MH.

OUTCOMES

The patient was successfully treated and discharged without any complications. Laboratory abnormalities were recovered to baseline at postoperative 4 days.

LESSONS

The authors suggest that possible MH susceptibility in DM1 patients may be refocused. Genetic testing can be a screening tool for MH susceptibility in these population, prior to receiving general anesthesia.

[Cardiac arrest under special circumstances]

These guidelines of the European Resuscitation Council (ERC) Cardiac Arrest under Special Circumstances are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. This section provides guidelines on the modifications required for basic and advanced life support for the prevention and treatment of cardiac arrest under special circumstances; in particular, specific causes (hypoxia, trauma, anaphylaxis, sepsis, hypo-/hyperkalaemia and other electrolyte disorders, hypothermia, avalanche, hyperthermia and malignant hyperthermia, pulmonary embolism, coronary thrombosis, cardiac tamponade, tension pneumothorax, toxic agents), specific settings (operating room, cardiac surgery, cardiac catheterization laboratory, dialysis unit, dental clinics, transportation [in-flight, cruise ships], sport, drowning, mass casualty incidents), and specific patient groups (asthma and chronic obstructive pulmonary disease, neurological disease, morbid obesity, pregnancy).

Secondary findings in 622 Turkish clinical exome sequencing data

CES (Clinical Exome Sequencing) is a method that we use to diagnose rare diseases with nonspesific clinical features. Besides primary indication for testing genetic information may be detected about diseases which have not yet emerged. ACMG guidelines recommend to report pathogenic variations in medically actionable 59 genes. In this study we evaluated CES data of 622 cases which were tested for various indications. According to ACMG recommendations 59 genes were screened for reportable variations. The detected variations were reviewed using distinct databases and ACMG variation classification guidelines. Among 622 cases 13 (2.1%) had reportable variations including oncogenetic, cardiogenetic disorders, and malignant hyperthermia susceptibility-related genes. In 15 cases (2.4%) heterozygous pathogenic and likely pathogenic variations were detected in genes showing autosomal recessive inheritance. Ten novel variations causing truncated protein or splicing defect were reported. We detected 11 variations having conflicting interpretations in databases and 30 novel variations, predicted as likely pathogenic via insilico analysis tools which further evaluations are needed. As to our knowledge this is the first study investigating secondary findings in Turkish population. To extract the information that may lead to prevent severe morbidities and mortalities from big data is a valuable and lifesaving effort. Results of this study will contrbute to existing knowledge about secondary findings in exome sequencing and will be a pioneer for studies in Turkish population.

European Resuscitation Council Guidelines 2021: Cardiac arrest in special circumstances

These European Resuscitation Council (ERC) Cardiac Arrest in Special Circumstances guidelines are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. This section provides guidelines on the modifications required to basic and advanced life support for the prevention and treatment of cardiac arrest in special circumstances; specifically special causes (hypoxia, trauma, anaphylaxis, sepsis, hypo/hyperkalaemia and other electrolyte disorders, hypothermia, avalanche, hyperthermia and malignant hyperthermia, pulmonary embolism, coronary thrombosis, cardiac tamponade, tension pneumothorax, toxic agents), special settings (operating room, cardiac surgery, catheter laboratory, dialysis unit, dental clinics, transportation (in-flight, cruise ships), sport, drowning, mass casualty incidents), and special patient groups (asthma and COPD, neurological disease, obesity, pregnancy).

Relevance of pathogenicity prediction tools in human RYR1 variants of unknown significance

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle metabolism characterized by generalized muscle rigidity, increased body temperature, rhabdomyolysis, hyperkalemia and severe metabolic acidosis. The underlying mechanism of MH involves excessive Ca²⁺ release from myotubes via the ryanodine receptor type 1 (RYR1) and the voltage-dependent L-type calcium channel (CACNA1S). As more than 300 variants of unknown significance have been detected to date, we examined whether freely available pathogenicity prediction tools are able to detect relevant MH causing variants. In this diagnostic accuracy study, blood samples from 235 individuals with a history of a clinical malignant hyperthermia or their close relatives were genetically screened for RYR1 variants of all 106 RYR1 exons and additionally for known variants of CACNA1S. In vitro contracture tests were conducted on muscle biopsies obtained from all individuals, independently of whether a pathogenic variant, a variant of unknown significance or no variant was detected. Comparisons were made to three established bioinformatic pathogenicity detection tools to identify the clinical impact of the variants of unknown significance. All detected genetic variants were tested for pathogenicity by three in silico approaches and compared to the in vitro contracture test. Sensitivity and specificity of exon screening of all individuals listed in our MH database was analyzed. Exon screening identified 97 (41%) of the 235 individuals as carriers of pathogenic variants. Variants of unknown significance were detected in 21 individuals. Variants of unknown significance were subdivided into 19 malignant-hyperthermia-susceptible individuals and 2 non-malignant-hyperthermia-susceptible individuals. All pathogenic variants as well as the malignant-hyperthermia-suspectible variants were correctly identified by the bioinformatic prediction tools. Sensitivity of in silico approaches ranged between 0.71 and 0.98 (Polyphen 0.94 [CI 95% 0.75; 0.99]; Sift 0.98 [CI 95% 0.81; 0.99]; MutationTaster 0.92 [CI 95% 0.75; 0.99]). Specificity differed depending on the used tool (Polphen 0.98 [CI 95% 0.32; 0.99]; Sift 0.98 [CI 95% 0.32; 0.99]; MutationTaster 0.00 [CI 95% 0.00; 0.60]). All pathogenic variants and variants of unknown significance were scored as probably damaging in individuals, demonstrating a high sensitivity. Specificity was very low in one of the three tested programs. However, due to potential genotype–phenotype discordance, bioinformatic prediction tools are currently of limited value in diagnosing pathogenicity of MH-susceptible variants.

Ryanodine receptor 1-related disorders: an historical perspective and proposal for a unified nomenclature

The RYR1 gene, which encodes the sarcoplasmic reticulum calcium release channel or type 1 ryanodine receptor (RyR1) of skeletal muscle, was sequenced in 1988 and RYR1 variations that impair calcium homeostasis and increase susceptibility to malignant hyperthermia were first identified in 1991. Since then, RYR1-related myopathies (RYR1-RM) have been described as rare, histopathologically and clinically heterogeneous, and slowly progressive neuromuscular disorders. RYR1 variants can lead to dysfunctional RyR1-mediated calcium release, malignant hyperthermia susceptibility, elevated oxidative stress, deleterious post-translational modifications, and decreased RyR1 expression. RYR1-RM-affected individuals can present with delayed motor milestones, contractures, scoliosis, ophthalmoplegia, and respiratory insufficiency.

Historically, RYR1-RM-affected individuals were diagnosed based on morphologic features observed in muscle biopsies including central cores, cores and rods, central nuclei, fiber type disproportion, and multi-minicores. However, these histopathologic features are not always specific to RYR1-RM and often change over time. As additional phenotypes were associated with RYR1 variations (including King-Denborough syndrome, exercise-induced rhabdomyolysis, lethal multiple pterygium syndrome, adult-onset distal myopathy, atypical periodic paralysis with or without myalgia, mild calf-predominant myopathy, and dusty core disease) the overlap among diagnostic categories is ever increasing. With the continuing emergence of new clinical subtypes along the RYR1 disease spectrum and reports of adult-onset phenotypes, nuanced nomenclatures have been reported (RYR1- [related, related congenital, congenital] myopathies). In this narrative review, we provide historical highlights of RYR1 research, accounts of the main diagnostic disease subtypes and propose RYR1-related disorders (RYR1-RD) as a unified nomenclature to describe this complex and evolving disease spectrum.

The Use of Continuous Blood Purification for the Treatment of Malignant Hyperthermia in an Infant

BACKGROUND

Malignant hyperthermia (MH) is a rare and potentially life-threatening pharmacogenetic disorder encountered during general anesthesia, with the incidence higher in children than in adults. Dantrolene is the specific antagonist of MH, but it is not readily available in China, thus developing alternative treatment protocols is of great practical importance.

CASE PRESENTATION

Herein, the authors report a two-month-old infant who underwent holmium laser epiglottis retrofitting through a bronchoscope, but developed limb muscular stiffness, tachypnea, tachycardia, and hyperthermia after sevoflurane exposure. After the diagnosis of MH, corresponding supportive treatment was implemented. Because there was no dantrolene available, continuous blood purification and mechanical ventilation were performed. A few days later, the boy recovered without any complications.

CONCLUSION

Based on the authors' successful clinical practice, the authors consider continuous blood purification as a reliable treatment for MH. But its feasibility still needs to be clarified after multicenter clinical observations.

Dietary Caffeine Synergizes Adverse Peripheral and Central Responses to Anesthesia in Malignant Hyperthermia Susceptible Mice

Ryanodine receptor (RYR) mutations confer stress-triggered malignant hyperthermia (MH) susceptibility. Dietary caffeine (CAF) is the most commonly consumed psychoactive compound by humans. CAF-triggered Ca2+ release and its influences on skeletal muscle contractility are widely used as experimental tools to study RYR function/dysfunction and diagnose MH susceptibility. We hypothesize that dietary CAF achieving blood levels measured in human plasma exacerbates the penetrance of RYR1 MH susceptibility mutations triggered by gaseous anesthetic, affecting both central and peripheral adverse responses. Heterozygous R163C-RYR1 (HET) MH susceptible mice are used to investigate the influences of dietary CAF on both peripheral and central responses before and after induction of halothane (HAL) maintenance anesthesia under experimental conditions that maintain normal core body temperature. HET mice receiving CAF (plasma CAF 893 ng/ml) have significantly shorter times to respiratory arrest compared with wild type, without altering blood chemistry or displaying hyperthermia or muscle rigor. Intraperitoneal bolus dantrolene before HAL prolongs time to respiratory arrest. A pilot electrographic study using subcutaneous electrodes reveals that dietary CAF does not alter baseline electroencephalogram (EEG) total power, but significantly shortens delay to isoelectric EEG, which precedes respiratory and cardiac arrest. CAF ± HAL are studied on RYR1 single-channel currents and HET myotubes to define molecular mechanisms of gene-by-environment synergism. Strong pharmacological synergism between CAF and HAL is demonstrated in both single-channel and myotube preparations. Central and peripheral nervous systems mediate adverse responses to HAL in a HET model of MH susceptibility exposed to dietary CAF, a modifiable lifestyle factor that may mitigate risks of acute and chronic diseases associated with RYR1 mutations. SIGNIFICANCE STATEMENT: Dietary caffeine at a human-relevant dose synergizes adverse peripheral and central responses to anesthesia in malignant hyperthermia susceptible mice. Synergism of these drugs can be attributed to their actions at ryanodine receptors.

Bioenergetic defects in muscle fibers of RYR1 mutant knock-in mice associated with malignant hyperthermia

Mutations in the skeletal muscle ryanodine receptor gene (RYR1) can cause susceptibility to malignant hyperthermia (MH), a potentially lethal genetic condition triggered by volatile anesthetics. MH is associated with hypermetabolism, which has directed research interest into oxidative phosphorylation and muscle bioenergetics. The most common cause of MH in the United Kingdom is the c.7300G>A RYR1 variant, which is present in ∼16% of MH families. Our study focuses on the MH susceptible G2435R-RYR1 knock-in mouse model, which is the murine equivalent of the human c.7300G>A genotype. Using a combination of transcriptomics, protein expression, and functional analysis, we investigated adult muscle fiber bioenergetics in this mouse model. RNA-Seq data showed reduced expression of genes associated with mitochondria and fatty acid oxidation in RYR1 mutants when compared with WT controls. Mitochondrial function was assessed by measuring oxygen consumption rates in permeabilized muscle fibers. Comparisons between WT and homozygous G2435R-RYR1 mitochondria showed a significant increase in complex I-facilitated oxidative phosphorylation in mutant muscle. Furthermore, we observed a gene-dose-specific increase in reactive oxygen species production in G2435R-RYR1 muscle fibers. Collectively, these findings provide evidence of metabolic defects in G2435R-RYR1 knock-in mouse muscle under basal conditions. Differences in metabolic profile could be the result of differential gene expression in metabolic pathways, in conjunction with mitochondrial damage accumulated from chronic exposure to increased oxidative stress.

Pharmacogenomics, concepts for the future of perioperative medicine and pain management: A review

Pharmacogenomics is the study of how genetic differences between individuals affect pharmacokinetics and pharmacodynamics. These differences are apparent to clinicians when taking into account the wide range of responses to medications given in clinical practice. A review of literature involving pharmacogenomics and pain management was performed. The implementation of preoperative pharmacogenomics will allow us to better care for our patients by delivering personalized, safer medicine. This review describes the current state of pharmacogenomics as it relates to many aspects of clinical practice and how clinicians can use these tools to improve patient outcomes.

Preclinical model systems of ryanodine receptor 1-related myopathies and malignant hyperthermia: a comprehensive scoping review of works published 1990-2019

BACKGROUND

Pathogenic variations in the gene encoding the skeletal muscle ryanodine receptor (RyR1) are associated with malignant hyperthermia (MH) susceptibility, a life-threatening hypermetabolic condition and RYR1-related myopathies (RYR1-RM), a spectrum of rare neuromuscular disorders. In RYR1-RM, intracellular calcium dysregulation, post-translational modifications, and decreased protein expression lead to a heterogenous clinical presentation including proximal muscle weakness, contractures, scoliosis, respiratory insufficiency, and ophthalmoplegia. Preclinical model systems of RYR1-RM and MH have been developed to better understand underlying pathomechanisms and test potential therapeutics.

METHODS

We conducted a comprehensive scoping review of scientific literature pertaining to RYR1-RM and MH preclinical model systems in accordance with the PRISMA Scoping Reviews Checklist and the framework proposed by Arksey and O'Malley. Two major electronic databases (PubMed and EMBASE) were searched without language restriction for articles and abstracts published between January 1, 1990 and July 3, 2019.

RESULTS

Our search yielded 5049 publications from which 262 were included in this review. A majority of variants tested in RYR1 preclinical models were localized to established MH/central core disease (MH/CCD) hot spots. A total of 250 unique RYR1 variations were reported in human/rodent/porcine models with 95% being missense substitutions. The most frequently reported RYR1 variant was R614C/R615C (human/porcine total n = 39), followed by Y523S/Y524S (rabbit/mouse total n = 30), I4898T/I4897T/I4895T (human/rabbit/mouse total n = 20), and R163C/R165C (human/mouse total n = 18). The dyspedic mouse was utilized by 47% of publications in the rodent category and its RyR1-null (1B5) myotubes were transfected in 23% of publications in the cellular model category. In studies of transfected HEK-293 cells, 57% of RYR1 variations affected the RyR1 channel and activation core domain. A total of 15 RYR1 mutant mouse strains were identified of which ten were heterozygous, three were compound heterozygous, and a further two were knockout. Porcine, avian, zebrafish, C. elegans, canine, equine, and drosophila model systems were also reported.

CONCLUSIONS

Over the past 30 years, there were 262 publications on MH and RYR1-RM preclinical model systems featuring more than 200 unique RYR1 variations tested in a broad range of species. Findings from these studies have set the foundation for therapeutic development for MH and RYR1-RM.

Intracellular calcium leak lowers glucose storage in human muscle, promoting hyperglycemia and diabetes

Most glucose is processed in muscle, for energy or glycogen stores. Malignant Hyperthermia Susceptibility (MHS) exemplifies muscle conditions that increase [Ca2+]cytosol. 42% of MHS patients have hyperglycemia. We show that phosphorylated glycogen phosphorylase (GPa), glycogen synthase (GSa) - respectively activated and inactivated by phosphorylation - and their Ca2+-dependent kinase (PhK), are elevated in microsomal extracts from MHS patients' muscle. Glycogen and glucose transporter GLUT4 are decreased. [Ca2+]cytosol, increased to MHS levels, promoted GP phosphorylation. Imaging at ~100 nm resolution located GPa at sarcoplasmic reticulum (SR) junctional cisternae, and apo-GP at Z disk. MHS muscle therefore has a wide-ranging alteration in glucose metabolism: high [Ca2+]cytosol activates PhK, which inhibits GS, activates GP and moves it toward the SR, favoring glycogenolysis. The alterations probably cause these patients' hyperglycemia. For basic studies, MHS emerges as a variable stressor, which forces glucose pathways from the normal to the diseased range, thereby exposing novel metabolic links.

Mouse model of severe recessive RYR1-related myopathy

Ryanodine receptor type I (RYR1)-related myopathies (RYR1 RM) are a clinically and histopathologically heterogeneous group of conditions that represent the most common subtype of childhood onset non-dystrophic muscle disorders. There are no treatments for this severe group of diseases. A major barrier to therapy development is the lack of an animal model that mirrors the clinical severity of pediatric cases of the disease. To address this, we used CRISPR/Cas9 gene editing to generate a novel recessive mouse model of RYR1 RM. This mouse (Ryr1TM/Indel) possesses a patient-relevant point mutation (T4706M) engineered into 1 allele and a 16 base pair frameshift deletion engineered into the second allele. Ryr1TM/Indel mice exhibit an overt phenotype beginning at 14 days of age that consists of reduced body/muscle mass and myofibre hypotrophy. Ryr1TM/Indel mice become progressively inactive from that point onward and die at a median age of 42 days. Histopathological assessment shows myofibre hypotrophy, increased central nuclei and decreased triad number but no clear evidence of metabolic cores. Biochemical analysis reveals a marked decrease in RYR1 protein levels (20% of normal) as compared to only a 50% decrease in transcript. Functional studies at end stage show significantly reduced electrically evoked Ca2+ release and force production. In summary, Ryr1TM/Indel mice exhibit a post-natal lethal recessive form of RYR1 RM that pheno-copies the severe congenital clinical presentation seen in a subgroup of RYR1 RM children. Thus, Ryr1TM/Indel mice represent a powerful model for both establishing the pathomechanisms of recessive RYR1 RM and pre-clinical testing of therapies for efficacy.

Single Amino Acid Changes in the Ryanodine Receptor in the Human Population Have Effects In Vivo on Caenorhabditis elegans Neuro-Muscular Function

The ryanodine receptor mediates intracellular calcium ion release with excitation of nerve and muscle cells. Ryanodine receptor missense variants cause a number of myopathologies, such as malignant hyperthermia, and have been linked with various neuropathologies, including Alzheimer's disease. We characterized the consequences of ryanodine receptor variants in vivo. Eight Caenorhabditis elegans strains, with ryanodine receptor modifications equivalent to human myopathic RYR1 variants, were generated by genome editing. In humans, these variants are rare and confer sensitivity to the inhalational anaesthetic halothane when heterozygous. Increased sensitivity to halothane was found in both homozygous and heterozygous C. elegans. Close analysis revealed distinct subtle locomotion defects, due to the different single amino acid residue changes, even in the absence of the external triggering agent. Distinct pre- and postsynaptic consequences of the variants were characterized through the responses to cholinergic pharmacological agents. The range of phenotypes reflects the complexity of the regulatory inputs to the ryanodine receptor and the criticality of the calcium ion channel opening properties, in different cell types and with age. Ryanodine receptors with these single amino acid residue changes still function as calcium ion channels, but with altered properties which are likely to have subtle consequences for human carriers of such variants. The long-term consequences of subtly altered calcium ion signalling could be cumulative and may be focussed in the smaller nerve cells rather than the more robust muscle cells. It was important to assess phenotypes in vivo to properly appreciate consequences for a whole organism.

Malignant Hyperthermia-Susceptible Adult Patient and Ambulatory Surgery Center: Society for Ambulatory Anesthesia and Ambulatory Surgical Care Committee of the American Society of Anesthesiologists Position Statement

This document represents a joint effort of the Society for Ambulatory Anesthesia (SAMBA) and the Ambulatory Surgical Care Committee of the American Society of Anesthesiologists (ASA) concerning the safe anesthetic care of adult malignant hyperthermia (MH)-susceptible patients in a free-standing ambulatory surgery center (ASC). Adult MH-susceptible patients can safely undergo a procedure in a free-standing ASC assuming that proper precautions for preventing, identifying, and managing MH are taken. The administration of preoperative prophylaxis with dantrolene is not indicated in MH-susceptible patients scheduled for elective surgery. There is no evidence to recommend an extended stay in the ASC, and the patient may be discharged when the usual discharge criteria for outpatient surgery are met. Survival from an MH crisis in an ASC setting requires early recognition, prompt treatment, and timely transfer to a center with critical care capabilities.

Prevalence of malignant hyperthermia diagnosis in obstetric patients in the United States, 2003 to 2014

Background

The cost-benefit of stocking dantrolene in maternity units for treating malignant hyperthermia (MH) has been recently questioned because of the low incidence of MH crisis in the general population and the low utilization of general anesthesia in obstetrics. However, no study has examined the prevalence of MH susceptibility in obstetrics. This study aimed to assess the prevalence of MH diagnosis and associated factors in obstetric patients.

Methods

Data for this study came from the National Inpatient Sample from 2003 to 2014, a 20% nationally representative sample of discharge records from community hospitals. A diagnosis of MH due to anesthesia was identified using the International Classification of Diseases, Ninth Revision, Clinical Modification code 995.86. MH prevalence was estimated according to the delivery mode and patient and hospital characteristics.

Results

During the 12-year study period, 47,178,322 delivery-related discharges [including 15,175,127 (32.2%) cesarean deliveries] were identified. Of them, 215 recorded a diagnosis of MH, yielding a prevalence of 0.46 per 100,000 [95% confidence interval (CI), 0.40 to 0.52]. The prevalence of MH diagnosis in cesarean deliveries was 0.81 per 100,000 (95% CI, 0.67 to 0.97), compared with 0.29 per 100,000 (95% CI, 0.23 to 0.35) in vaginal deliveries (P <  0.001). Multivariable logistic regression revealed that cesarean delivery was associated with a significantly increased risk of MH diagnosis [adjusted rate ratio (aOR) 2.88; 95% CI, 2.19 to 3.80]. Prevalence of MH diagnosis was lower in Hispanics than in non-Hispanic whites (aOR 0.47; 95% CI, 0.29 to 0.76) and higher in the South than in the Northeast census regions (aOR 2.44; 95% CI, 1.50 to 3.96).

Conclusion

The prevalence of MH-susceptibility is about 1 in 125,000 in cesarean deliveries, similar to the prevalence reported in non-obstetrical surgery inpatients. The findings of this study suggest that stocking dantrolene in maternity units is justified.

Perioperative Neurocognitive Disorder: State of the Preclinical Science

The purpose of this article is to provide a succinct summary of the different experimental approaches that have been used in preclinical postoperative cognitive dysfunction research, and an overview of the knowledge that has accrued. This is not intended to be a comprehensive review, but rather is intended to highlight how the many different approaches have contributed to our understanding of postoperative cognitive dysfunction, and to identify knowledge gaps to be filled by further research. The authors have organized this report by the level of experimental and systems complexity, starting with molecular and cellular approaches, then moving to intact invertebrates and vertebrate animal models. In addition, the authors' goal is to improve the quality and consistency of postoperative cognitive dysfunction and perioperative neurocognitive disorder research by promoting optimal study design, enhanced transparency, and "best practices" in experimental design and reporting to increase the likelihood of corroborating results. Thus, the authors conclude with general guidelines for designing, conducting and reporting perioperative neurocognitive disorder rodent research.

The current status of malignant hyperthermia

Malignant hyperthermia (MH) is a rare and life-threatening pharmacogenetic disorder triggered by volatile anesthetics, the depolarizing muscle relaxant succinylcholine, and rarely by strenuous exercise or environmental heat. The exact prevalence of MH is unknown, and it varies from 1:16 000 in Denmark to 1:100 000 in New York State. The underlying mechanism of MH is excessive calcium release from the sarcoplasmic reticulum (SR), leading to uncontrolled skeletal muscle hyper-metabolism. Genetic mutations in ryanodine receptor type 1 ( RYR1) and CACNA1S have been identified in approximately 50% to 86% and 1% of MH-susceptible (MHS) individuals, respectively. Classic clinical symptoms of MH include hypercarbia, sinus tachycardia, masseter spasm, hyperthermia, acidosis, muscle rigidity, hyperkalemia, myoglobinuria, and etc. There are two types of testing for MH: a genetic test and a contracture test. Contracture testing is still being considered as the gold standard for MH diagnosis. Dantrolene is the only available drug approved for the treatment of MH through suppressing the calcium release from SR. Since clinical symptoms of MH are highly variable, it can be difficult to establish a diagnosis of MH. Nevertheless, prompt diagnosis and treatments are crucial to avoid a fatal outcome. Therefore, it is very important for anesthesiologists to raise awareness and understand the characteristics of MH. This review summarizes epidemiology, clinical symptoms, diagnosis and treatments of MH and any new developments.

Neuromuscular Diseases of the Newborn

The peripheral nervous system (PNS) is composed of motor neurons, nerve roots, plexuses, peripheral nerves (motor, sensory and autonomic), neuromuscular junction, and skeletal muscles. Disorders of the PNS in neonates most frequently cause weakness, hypotonia, and contractures, which may be generalized or focal. Since these findings may also occur with brain and spinal cord lesions, key features of the history and neurologic exam, together with diagnostic testing, are helpful in reaching a diagnosis. This review covers the diagnostic approach to PNS disorders in the neonate and includes a discussion of representative diseases of the motor neuron, brachial plexus, peripheral nerves, neuromuscular junction, and muscles. The importance of reaching a precise genetic diagnosis is highlighted with a discussion of current and emerging treatments for neonatal PNS diseases, particularly spinal muscular atrophy.