Exercise-induced rhabdomyolysis and stress-induced malignant hyperthermia events, association with malignant hyperthermia susceptibility, and RYR1 gene sequence variations

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.

Integration of yoga within exercise and sports science as a preventive and management strategy for musculoskeletal injuries/disorders and mental disorders - A review of the literature

OBJECTIVES

Exercise-induced musculoskeletal injuries/disorders and associated mental disorders are prevalent among athletes. The main objective of this review is to analyze the prospects of Yoga practices as a preventive and management strategy for musculoskeletal injuries/disorders and associated mental disorders often encountered in exercise and sports activities.

METHODS

A review of the literature was performed using electronic databases such as MEDLINE/PubMed and google scholar published between January 1991 and December 2021 which yielded 88 research articles. The keywords used were yoga OR exercise AND musculoskeletal injuries OR disorders, yoga OR exercise AND mental disorders, yoga AND sports injuries, yoga AND stress, yoga OR exercise AND oxidative stress, yoga OR exercise AND inflammation, yoga OR exercise AND diet.

RESULTS

The moderate and regular exercises are beneficial to health. However, high intensity and overtraining physical activities lead to immune suppression, oxidative stress, muscle damage/fatigue, coronary risk, psychiatric disorders and so on due to enormous strain on various physiological functions. Yoga seems to undermine these adverse activities through up-regulating the functions of the parasympathetic nervous system (PNS) and down-regulating the activities of hypothalamohypophysial axis (HPA) which are conducive to healing, recovery, regeneration, reduction in stress, relaxation of mind, better cognitive functions, promotion of mental health, reduction in inflammation and oxidative stress, and so on.

CONCLUSION

Literature suggests that Yoga should be integrated within exercise and sports sciences mainly to prevent & manage musculoskeletal injuries/disorders and associated mental disorders.

Impact of rhabdomyolysis on outcomes of hospitalizations for heat stroke in the United States

BACKGROUND

The objective of this study was to evaluate the predictors and associated outcomes of rhabdomyolysis in admitted patients for heat stroke in the United States.

METHODS

The National Inpatient Sample was utilized to identify hospitalized patients with a primary diagnosis of heat stroke from the years 2003-2014. Rhabdomyolysis was identified using hospital diagnosis code. We compared the clinical characteristics, in-hospital treatment, complications, outcomes, and resource utilization between patients with and without rhabdomyolysis.

RESULTS

A total of 3,372 hospital admissions for heat stroke were studied. Of these, rhabdomyolysis occurred in 1049 (31%) admissions. The risk factors for rhabdomyolysis were age 20-39 years, male sex, African American race, history of alcohol drinking, whereas age ≥60 years, smoking, history of diabetes mellitus, and hypertension were associated with lower risk of rhabdomyolysis. Patients with rhabdomyolysis had greater requirements for mechanical ventilation, blood component transfusion, and renal replacement therapy. Rhabdomyolysis was significantly associated with increased risk of hyponatremia, hypernatremia, hyperkalemia, hypocalcemia, serum phosphorus and magnesium derangement, metabolic acidosis, sepsis, ventricular arrhythmia or cardiac arrest, renal failure, respiratory failure, liver failure, neurological failure, hematologic failure, and in-hospital mortality. Length of hospital stay and hospitalization cost were higher when rhabdomyolysis occurred during hospital stay.

CONCLUSION

Rhabdomyolysis occurred in about one-third of hospitalized patients for heat stroke and was associated with increased morbidity, mortality, and resource utilization.

Adaptive thermogenesis enhances the life-threatening response to heat in mice with an Ryr1 mutation

Mutations in the skeletal muscle Ca2+ release channel, the type 1 ryanodine receptor (RYR1), cause malignant hyperthermia susceptibility (MHS) and a life-threatening sensitivity to heat, which is most severe in children. Mice with an MHS-associated mutation in Ryr1 (Y524S, YS) display lethal muscle contractures in response to heat. Here we show that the heat response in the YS mice is exacerbated by brown fat adaptive thermogenesis. In addition, the YS mice have more brown adipose tissue thermogenic capacity than their littermate controls. Blood lactate levels are elevated in both heat-sensitive MHS patients with RYR1 mutations and YS mice due to Ca2+ driven increases in muscle metabolism. Lactate increases brown adipogenesis in both mouse and human brown preadipocytes. This study suggests that simple lifestyle modifications such as avoiding extreme temperatures and maintaining thermoneutrality could decrease the risk of life-threatening responses to heat and exercise in individuals with RYR1 pathogenic variants.

Update on Congenital Myopathies in Adulthood

Congenital myopathies (CMs) constitute a group of heterogenous rare inherited muscle diseases with different incidences. They are traditionally grouped based on characteristic histopathological findings revealed on muscle biopsy. In recent decades, the ever-increasing application of modern genetic technologies has not just improved our understanding of their pathophysiology, but also expanded their phenotypic spectrum and contributed to a more genetically based approach for their classification. Later onset forms of CMs are increasingly recognised. They are often considered milder with slower progression, variable clinical presentations and different modes of inheritance. We reviewed the key features and genetic basis of late onset CMs with a special emphasis on those forms that may first manifest in adulthood.

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.

Exertional rhabdomyolysis: Relevance of clinical and laboratory findings, and clues for investigation

Some degree of exertional rhabdomyolysis (ER), striated muscle breakdown associated with strenuous exercise, is a well-known phenomenon associated with endurance sports. However in rare cases, severe and/or recurrent ER is a manifestation of an underlying condition, which puts patients at risk for significant morbidity and mortality. Selecting the patients that need a diagnostic work up of an acute rhabdomyolysis episode is an important task.

Based on the diagnostic work up of three illustrative patients treated in our hospital, retrospectively using the ‘RHABDO’ screening tool, we discuss the clinical and biochemical clues that should trigger further investigation for an underlying condition. Finally, we describe the most common genetic causes of this clinical syndrome.

RYR1 Sequence Variants in Myopathies: Expression and Functional Studies in Two Families

The skeletal muscle ryanodine receptor (RyR1), i.e., the Ca²⁺ channel of the sarco/endoplasmic reticulum (S/ER), and the voltage-dependent calcium channel Cav1.1 are the principal channels involved in excitation-contraction coupling in skeletal muscle. RYR1 gene variants are linked to distinct skeletal muscle disorders, including malignant hyperthermia susceptibility and central core disease (CCD), mainly with autosomal dominant inheritance, and autosomal recessive myopathies with a broad phenotypic and histopathological spectrum. The age at onset of RYR1-related myopathies varies from infancy to adulthood. We report the identification of four RYR1 variants in two Italian families: one with myopathy and variants c.4003C>T (p.R1335C) and c.7035C>A (p.S2345R), and another with CCD and variants c.9293G>T (p.S3098I) and c.14771_14772insTAGACAGGGTGTTGCTCTGTTGCCCTTCTT (p.F4924_V4925insRQGVALLPFF). We demonstrate that, in patient-specific lymphoblastoid cells, the c.4003C>T (p.R1335C) variant is not expressed and the in-frame 30-nucleotide insertion variant is expressed at a low level. Moreover, Ca²⁺ release in response to the RyR1 agonist 4-chloro-m-cresol and to thapsigargin showed that the c.7035C>A (p.S2345R) variant causes depletion of S/ER Ca²⁺ stores and that the compound heterozygosity for variant c.9293G>T (p.S3098I) and the 30-nucleotide insertion increases RyR1-dependent Ca²⁺ release without affecting ER Ca²⁺ stores. In conclusion, we detected and functionally characterized disease-causing variants of the RyR1 channel in patient-specific lymphoblastoid cells.

This paper is dedicated to the memory and contribution of Luigi Del Vecchio.

Phenotype and genotype of muscle ryanodine receptor rhabdomyolysis-myalgia syndrome

OBJECTIVES

Rhabdomyolysis and myalgia are common conditions, and mutation in the ryanodine receptor 1 gene (RYR1) is suggested to be a common cause. Due to the large size of RYR1, however, sequencing has not been widely accessible before the recent advent of next-generation sequencing technology and limited phenotypic descriptions are therefore available.

MATERIAL & METHODS

We present the medical history, clinical and ancillary findings of patients with RYR1 mutations and rhabdomyolysis and myalgia identified in Denmark, France and The Netherlands.

RESULTS

Twenty-two patients with recurrent rhabdomyolysis (CK > 10 000) or myalgia with hyperCKemia (>1.5 × ULN) and a RYR1 mutation were identified. One had mild wasting of the quadriceps muscle, but none had fixed weakness. Symptoms varied from being restricted to intense exercise to limiting ADL function. One patient developed transient kidney failure during rhabdomyolysis. Two received immunosuppressants on suspicion of myositis. None had episodes of malignant hyperthermia. Muscle biopsies were normal, but CT/MRI showed muscle hypertrophy in most. Delay from first symptom to diagnosis was 12 years on average. Fifteen different dominantly inherited mutations were identified. Ten were previously described as pathogenic and 5 were novel, but rare/absent from the background population, and predicted to be pathogenic by in silico analyses. Ten of the mutations were reported to give malignant hyperthermia susceptibility.

CONCLUSION

Mutations in RYR1 should be considered as a significant cause of rhabdomyolysis and myalgia syndrome in patients with the characteristic combination of rhabdomyolysis, myalgia and cramps, creatine kinase elevation, no weakness and often muscle hypertrophy.

Aerobic Training Prevents Heatstrokes in Calsequestrin-1 Knockout Mice by Reducing Oxidative Stress

Calsequestrin-1 knockout (CASQ1-null) mice suffer lethal episodes when exposed to strenuous exercise and environmental heat, crises known as exertional/environmental heatstroke (EHS). We previously demonstrated that administration of exogenous antioxidants (N-acetylcysteine and trolox) reduces CASQ1-null mortality during exposure to heat. As aerobic training is known to boost endogenous antioxidant protection, we subjected CASQ1-null mice to treadmill running for 2 months at 60% of their maximal speed for 1 h, 5 times/week. When exposed to heat stress protocol (41°C/1 h), the mortality rate of CASQ1-null mice was significantly reduced compared to untrained animals (86% versus 16%). Protection from heatstrokes was accompanied by a reduced increase in core temperature during the stress protocol and by an increased threshold of response to caffeine of isolated extensor digitorum longus muscles during in vitro contracture test. At cellular and molecular levels, aerobic training (i) improved mitochondrial function while reducing their damage and (ii) lowered calpain activity and lipid peroxidation in membranes isolated from sarcoplasmic reticulum and mitochondria. Based on this evidence, we hypothesize that the protective effect of aerobic training is essentially mediated by a reduction in oxidative stress during exposure of CASQ1-null mice to adverse environmental conditions.

Pathophysiology of heatstroke in dogs - revisited

Heatstroke results from a failure to dissipate accumulated heat during exposure to hot environments, or during strenuous physical exercise under heat stress. It is characterized by core body temperatures > 41°C, with central nervous system dysfunction. Functional morphology and thermoregulatory effectors differences between dogs and humans may require special heatstroke protective adaptations in dogs, however, the risk factors for developing heatstroke are similar in both. In dogs, these include hot, especially highly humid environments, excessive physical activity, obesity, large (>15 kg) body weight, being of certain breed (e.g., Labrador retrievers and brachycephalic breeds), upper airway obstruction and prolonged seizures. Lack of acclimation to heat and physical fitness decreases the survival of heat stroked dogs. At the systemic level, blood pooling within the large internal organs (e.g., spleen, liver) is a major contributor to the development of shock and consequent intestinal ischemia, hypoxia and endothelial hyperpermeability, commonly occurring in heatstroke patients. Evoked serious complications include rhabdomyolysis, acute kidney injury, acute respiratory distress syndrome and ultimately, sepsis and disseminated intravascular coagulation. The most common clinical signs in dogs include acute collapse, tachypnea, spontaneous bleeding, shock signs and mental abnormalities, including depression, disorientation or delirium, seizures, stupor and coma. In such dogs, presence of peripheral blood nucleated red blood cells uniquely occurs, and is a highly sensitive diagnostic and prognostic biomarker. Despite early, appropriate body cooling, and intensive supportive treatment, with no available specific treatment to ameliorate the severe inflammatory and hemostatic derangements, the mortality rate is around 50%, similar to that of human heatstroke victims. This review discusses the pathophysiology of canine heatstroke from a veterinarian's point of view, integrating new and old studies and knowledge.

RYR1-related rhabdomyolysis: A common but probably underdiagnosed manifestation of skeletal muscle ryanodine receptor dysfunction

Mutations in the skeletal muscle ryanodine receptor (RYR1) gene are associated with a wide spectrum of inherited myopathies presenting throughout life. Malignant hyperthermia susceptibility (MHS)-related RYR1 mutations have emerged as a common cause of exertional rhabdomyolysis, accounting for up to 30% of rhabdomyolysis episodes in otherwise healthy individuals. Common triggers are exercise and heat and, less frequently, viral infections, alcohol and drugs. Most subjects are normally strong and have no personal or family history of malignant hyperthermia. Heat intolerance and cold-induced muscle stiffness may be a feature. Recognition of this (probably not uncommon) rhabdomyolysis cause is vital for effective counselling, to identify potentially malignant hyperthermia-susceptible individuals and to adapt training regimes. Studies in various animal models provide insights regarding possible pathophysiological mechanisms and offer therapeutic perspectives.

Is It Exertional Heatstroke or Something More? A Case Report

BACKGROUND

Heat stroke, heat-related illness, and malignant hyperthermia all present with hyperthermia. The former two are common presentations in the emergency department (ED). On the other hand, malignant hyperthermia (MH) is an uncommon but equally dangerous condition that requires prompt recognition and specific treatment with dantrolene sodium and avoidance of certain medications to reduce morbidity and mortality. Recent research focusing on nonanesthetic or exercise-induced MH has demonstrated a relationship between certain gene mutations and malignant hyperthermia susceptibility.

CASE REPORT

We report the case of a 19 year-old man with a family history of MH who was treated for exertional heat stroke, but despite cooling and adequate fluid resuscitation, demonstrated worsening rhabdomyolysis that subsequently responded to the administration of dantrolene sodium. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case illustrates the importance of recognizing the potential relationship between exertional heat stroke and malignant hyperthermia. The overlap between heat stroke and malignant hyperthermia susceptibility has important implications in the treatment and evaluation of patients presenting with signs and symptoms of heat stroke or heat-related illness in the ED.

Exertional Heat Stroke and Susceptibility to Malignant Hyperthermia in an Athlete: Evidence for a Link?

OBJECTIVE

To describe the possible association (pathophysiologic and clinical features) between exertional heat stroke (EHS) and malignant hyperthermia (MH).

BACKGROUND

Both EHS and MH are acute and life-threatening disorders. It has repeatedly been shown that EHS can occur in well-trained patients with known MH-associated mutation in the RYR1 gene in the absence of any extreme environmental conditions or extreme physical activity, thereby supporting a possible link between EHS and MH. In this case, a highly trained 30-year-old male athlete suddenly collapsed while running. He had initial hyperthermia (40.2°C) and progressive multiple organ failure requiring medical management in an intensive care unit. After he recovered completely, a maximal exercise test was performed and showed an obvious abnormality of oxidative metabolism in muscle; genetic analysis of the RYR1 gene identified a heterozygous missense variation p.K1393R. Consequently, the athlete was given appropriate information and allowed to progressively return to sport competition.

DIFFERENTIAL DIAGNOSIS

Doping, use of drugs and toxic agents, exercise-associated hyponatremia, exertional heat illness.

TREATMENT

Initial management started with the basic resuscitative guidelines of airway, breathing, and circulation (intubation). Cooling, administration of fresh frozen plasma, and intensive rehydration resulted in improvement.

UNIQUENESS

To our knowledge, ours is the first description of this MH mutation (p.K1393R) in the RYR1 gene that was associated with exertional rhabdomyolysis involving a dramatic impairment of oxidative metabolism in muscle.

CONCLUSIONS

Common features are shared by EHS and MH. Careful attention must therefore be paid to athletes who experience EHS, especially in temperate climates or when there are no other predisposing factors.

Hypothesis: exertional heat stroke-induced myopathy and genetically inherited malignant hyperthermia represent the same disorder, the human stress syndrome

Exertional heat stroke is usually experienced as a result of a prolonged and intensive exercise. It is a life-threatening condition that is characterized by an increase in core body temperature and rhabdomyolysis. The associated hyperkalemia and metabolic acidosis may lead to an acute renal, cardiac, and hemostatic failure. Exactly, the same symptoms are noticed in case of the anesthesia-induced malignant hyperthermia (MH), an inherited disorder of the skeletal muscle ryanodine receptor. This receptor is a Ca(2+) channel that is activated by the volatile anesthetic agents and depolarizing muscle relaxant. The presence of MH-associated ryanodine receptor variant in the individuals who suffered from EH and improvement of the symptoms with dantrolene has frequently raised the question as to whether the two disorders actually represent one and the same disease. Nevertheless, an exact explanation of the susceptibility of the genetically predisposed MH individuals to ER remains elusive. We have attempted to review the published clinical reports to explore the possibility that ER and EH represent one and the same disorder.

RYR1-related myopathies: a wide spectrum of phenotypes throughout life

BACKGROUND AND PURPOSE

Although several recent studies have implicated RYR1 mutations as a common cause of various myopathies and the malignant hyperthermia susceptibility (MHS) trait, many of these studies have been limited to certain age groups, confined geographical regions or specific conditions. The aim of the present study was to investigate the full spectrum of RYR1-related disorders throughout life and to use this knowledge to increase vigilance concerning malignant hyperthermia.

METHODS

A retrospective cohort study was performed on the clinical, genetic and histopathological features of all paediatric and adult patients in whom an RYR1 mutation was detected in a national referral centre for both malignant hyperthermia and inherited myopathies (2008-2012).

RESULTS

The cohort of 77 non-related patients (detection rate 28%) included both congenital myopathies with permanent weakness and 'induced' myopathies such as MHS and non-anaesthesia-related episodes of rhabdomyolysis or hyperCKemia, manifested throughout life and triggered by various stimuli. Sixty-one different mutations were detected, of which 24 were novel. Some mutations are present in both dominant (MHS) and recessive modes (congenital myopathy) of inheritance, even within families. Histopathological features included an equally wide spectrum, ranging from only subtle abnormalities to prominent cores.

CONCLUSIONS

This broad range of RYR1-related disorders often presents to the general paediatric and adult neurologist. Its recognition is essential for genetic counselling and improving patients' safety during anaesthesia. Future research should focus on in vitro testing by the in vitro contracture test and functional characterization of the large number of RYR1 variants whose precise effects currently remain uncertain.

Rhabdomyolysis: a genetic perspective

Rhabdomyolysis (RM) is a clinical emergency characterized by fulminant skeletal muscle damage and release of intracellular muscle components into the blood stream leading to myoglobinuria and, in severe cases, acute renal failure. Apart from trauma, a wide range of causes have been reported including drug abuse and infections. Underlying genetic disorders are also a cause of RM and can often pose a diagnostic challenge, considering their marked heterogeneity and comparative rarity.

In this paper we review the range of rare genetic defects known to be associated with RM. Each gene has been reviewed for the following: clinical phenotype, typical triggers for RM and recommended diagnostic approach. The purpose of this review is to highlight the most important features associated with specific genetic defects in order to aid the diagnosis of patients presenting with hereditary causes of recurrent RM.

Diagnostic evaluation of rhabdomyolysis

Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.

Safe duration of postoperative monitoring for malignant hyperthermia patients administered non-triggering anaesthesia: an update

The postoperative care of malignant hyperthermia (MH) patients is subject to international variation, with a paucity of data in the literature to guide management. Over a series of three studies, our aim was to evaluate whether MH-susceptible patients (and relatives who had not yet been investigated), who had received a non-triggering anaesthetic, could be managed in the same way as the standard surgical population. Following a retrospective study, 206 anaesthetics were administered in a prospective second study to MH-susceptible/related individuals who were monitored for a minimum of one hour in the post anaesthesia care unit and a further 90 minutes in a step-down facility. No problems relating to MH were encountered. The postoperative monitoring time was subsequently changed and, in a third study, patients were managed no differently from standard surgical patients. One hundred and twenty-five anaesthetics were administered with no evidence of problems. This data shows that standard postoperative monitoring times are safe and appropriate in MH-susceptible patients.

Anesthetic considerations in myofibrillar myopathy

Myofibrillar myopathy (MFM) is a relatively newly recognized genetic disease that leads to progressive muscle deterioration. MFM has a varied phenotypic presentation and impacts cardiac, skeletal, and smooth muscles. Affected individuals are at increased risk of respiratory failure, significant cardiac conduction abnormalities, cardiomyopathy, and sudden cardiac death. In addition, significant skeletal muscle involvement is common, which may lead to contractures, respiratory insufficiency, and airway compromise as the disease progresses. This study is the first report of anesthetic management of a patient with MFM. We report multiple anesthetic encounters of a child with genetically confirmed BAG3-myopathy, a subtype of MFM with severe childhood disease onset. A review of the anesthetic implications of the disease is provided, with specific exploration of possible susceptibility to malignant hyperthermia, rhabdomyolysis, and sensitivity to other anesthetic agents.

The disorders of the calcium release unit of skeletal muscles: what have we learned from mouse models?

Calcium storage, release, and reuptake are essential for normal physiological function of muscle. Several human skeletal muscle disorders can arise from dysfunction in the control and coordination of these three critical processes. The release from the Sarcoplasmic Reticulum stores (SR) is handled by a multiprotein complex called Calcium Release Unit and composed of DiHydroPyridine Receptor or DHPR, Ryanodine Receptor or RYR, Calsequestrin or CASQ, junctin, Triadin, Junctophilin and Mitsugumin 29. Malignant hyperthermia (MH), Central Core Disease (CCD), Exertional/environmental Heat Stroke (EHS) and Multiminicore disease (MmD) are inherited disorders of calcium homeostasis in skeletal muscles directly related to mutations of genes coding for proteins of the CRU, primarily ryanodine receptor (RYR1). To understand the pathophysiology of MH and CCD, four murine lines carrying point mutations of human RYR1 have been developed: Y524S, R163C, I4898T and T4826I. Mice carrying those mutations show a phenotype with the traits of MH and/or CCD. Interestingly, also ablation of skeletal muscle calsequestrin (CASQ1) leads to a phenotype with MH-like lethal episodes in response to halothane and heat stress and development of central cores. In this review, we aim to describe the murine lines with RYR mutations or CASQ ablation, which show a phenotype similar to human MH or CCD, to underline their specific phenotypes and their differences and to discuss their contribution to the understanding of the pathophysiology of the disorders and the development of therapeutic strategies.

Unexpected MH deaths without exposure to inhalation anesthetics in pediatric patients

Children, later found to have ryanodine receptor type one variants (RYR1), died without exposure to inhalation anesthetics. Family members with the same RYR1 variants had contracture tests consistent with susceptibility to malignant hyperthermia or in vitro testing showed increased sensitivity to RYR1 agonist.