The genetics of malignant hyperthermia: Evidence for heterogeneity

Study of phenotype and familial distribution of malignant hyperthermia (MH) suggests heterogeneity with MH possibly being a symptom of several disorders. Review of all reported family studies supports the concept of heterogeneity with autosomal dominant inheritance in about one-half of the families. There is no strong evidence for other mendelian patterns of inheritance, but sporadic and possibly multifactorially determined cases are common. MH is also seen in other musculoskeletal disorders. We report 12 Wisconsin families with MH and outline a preliminary approach to the counseling of MH patients and their families.     

Novel skeletal muscle ryanodine receptor mutation in a large Brazilian family with malignant hyperthermia

Malignant hyperthermia (MH) is an autosomal dominant disorder that predisposes susceptible individuals to a potentially life-threatening crisis when exposed to commonly used anesthetics. Mutations in the skeletal muscle calcium release channel, ryanodine receptor (RYR1) are associated with MH in over 50% of affected families. Linkage analysis of the RYR1 gene region at 19q13 was performed in a large Brazilian family and a distinct disease co-segregating haplotype was revealed in the majority of members with diagnosis of MH. Subsequent sequencing of RYR1 mutational hot spots revealed a nucleotide substitution of C to T at position 7062, causing a novel amino acid change from Arg2355 to Cys associated with MH in the family. Haplotype analysis of the RYR1 gene area at 19q13 in the family with multiple MH members is an important tool in identification of genetic cause underlying this disease.     

Determination of a positive malignant hyperthermia (MH) disposition without the in vitro contracture test in families carrying the RYR1 Arg614Cys mutation

Molecular genetic methods are used with caution for determining positive malignant hyperthermia (MH) disposition in clinical MH diagnosis because of the genetic variability of this disease. But under defined conditions, genotyping can have an advantage over the standardized in vitro contracture test (IVCT) in respect of invasive approach, specificity, patient compliance, and the work and expense involved in the method. We aim to demonstrate this using 10 families with the Arg614Cys mutation in the ryanodine receptor as an example. Fifty-one index patients who had been classified as MH-susceptible (MHS) in the IVCT (European MH protocol) after a clinical MH incident or suspected MH were screened for the Arg614Cys (C1840-->T) mutation in the RYR1 gene because this mutation is more common in German MH families (9%). The family members of those index patients, in whom a Arg614Cys mutation was detectable, were also screened for the presence of this mutation (n=136), and the results were subjected to a more detailed analysis including existing IVCT findings (n=71). The Arg614Cys mutation was identified in a total of 64 members of the 10 independent families. In 35 individuals in this group, there was a definite concordance between the MHS diagnosis in the IVCT and the presence of the Arg614Cys mutation. No individual phenotyped as MH-negative carried the mutation. On the basis of the guidelines of the EMHG for molecular genetic detection of MH susceptibility, 29 individuals who bore the Arg614Cys mutation were classified as MHS without the IVCT. If a causal mutation is detected in an MH family, the MHS diagnosis can be deduced without the invasive IVCT in all other mutation carriers. Despite inclusion of only one (Arg614Cys) of all known MH mutations, the study emphasizes the practical use of a genetic approach for determination of a positive MH diagnosis.     

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.     

Genetic recombination between malignant hyperthermia and calcium release channel in skeletal muscle

Absolute linkage between the gene, on chromosome 19, for the calcium release channel (CRC) of the sarcoplasmic reticulum in skeletal muscle and malignant hyperthermia (MH) has been reported by other workers. In the present study of three Swedish Families informative with respect to this linkage relationship, definite recombinants were found in two families. We conclude that mutations in other genes than the CRC gene can cause the clinical picture of MH. Accordingly, MH appears to be genetically heterogeneous.     

Linkage studies of Myotonia congenita and Paramyotonia congenita

Six German families segregating for Myotonia congenita (MC) and eight families from Germany and Great Britain with Paramyotonia congenita (PC) were tested for linkage relationships using 35 serological and biochemical markers. No linkage of MC to any of the markers was evident, but a positive sum of lod scores for PC vs. the HP locus (z = 1.16, theta = 0.16) was found. The results encourage further investigations involving chromosome 16 markers.     

Failure of norepinephrine to initiate procine malignant hyperthermia

Continuous intravenous infusion in pigs of norepinephrine, to blood concentrations of 140 ng.ml^–1, provided a test of the hypothesis that this sympathetic hormone can initiate malignant hyperthermia (MH). This study was performed during nitrous oxidepentobarbital anesthesia, and in part utilized sodium nitroprusside to maintain normal blood pressure and peripheral perfusion. Metabolic stimulation, or evidence of MH, did not occur in normal of susceptible pigs, as indicated by the lack of increase in both whole body O₂ consumption and arterial lactate concentration. Next, in contrast, susceptible pigs manifested MH when exposed to halothane and succinylcholine, while normal pigs did not. We conclude that norepinephrine does not mediate or initiate porcine whole body stress responses characteristic of MH.     

Epidemiological and clinical features of malignant hyperthermia: A scoping review

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

Discordance between malignant hyperthermia susceptibility and RYR1 mutation C1840T in two Scandinavian MH families exhibiting this mutation

The ryanodine receptor 1 (RYR1) mutation C1840T has been reported to segregate with malignant hyperthermia (MH) susceptibility in several families. We have investigated several Scandinavian MH families with respect to five different RYR1 mutations reported to cause predisposition to MH, and we here report on two of the families in which the C1840T mutation was detected. In these two families there was recombination between MH susceptibility and this mutation in one and three individuals, respectively. These findings may suggest that it is necessary to reconsider the specificity of the IVCT and the role of C1840T as a cause of MH susceptibility in some families exhibiting this mutation.     

Next‐generation DNA sequencing of a Swedish malignant hyperthermia cohort

Malignant hyperthermia (MH)‐related mutations have been identified in the ryanodine receptor type 1 gene (RYR1) and in the dihydropyridine gene (CACNA1S), but about half of the patients do not have causative mutations in these genes. We wanted to study the contribution of other muscle genes to the RYR1 phenotypes. We designed a gene panel for sequence enrichment targeting 64 genes of proteins involved in the homeostasis of the striated muscle cell. Next‐generation sequencing (NGS) resulted in >50,000 sequence variants which were further analyzed by software filtering criteria to identify causative variants. In four of five patients we identified previously reported RYR1 mutations while the fifth patient did not show any candidate variant in any of the genes investigated. In two patients pathogenic variants were found in other genes known to cause a muscle disorders. All but one patient carried likely benign rare polymorphisms. The NGS technique proved convenient in identifying variants in the RYR1. However, with a clinically variable phenotype‐like MH, the pre‐selection of genes poses problems in variant interpretation.     

Increased sensitivity to 4-chloro-m-cresol and caffeine in primary myotubes from malignant hyperthermia susceptible individuals carrying the ryanodine receptor 1 Thr2206Met (C6617T) mutation

Malignant hyperthermia (MH) is an autosomal-dominant disorder of skeletal muscle, triggered by volatile anaesthetics and depolarizing muscle relaxants. The causative defect lies in the control of Ca(2+) release from the sarcoplasmic reticulum in skeletal muscle. Numerous mutations have been detected in the ryanodine receptor 1 (RyR1) gene, but so far an MH-causative role has only been confirmed for 16 human RyR1 mutations. In this report we show that myotubes derived from individuals carrying the RyR1 Thr2206Met (C6617T) mutation have an abnormal response of the intracellular calcium concentration to 4-chloro-m-cresol and to caffeine. Satellite cells were obtained from muscle biopsies of patients referred for diagnosing MH. The intracellular calcium concentration in response to 4-chloro-m-cresol and to caffeine was investigated by fluorescence calcium imaging. In myotubes the half-maximal activation concentration (EC(50)) for 4-chloro-m-cresol was reduced from 203 micro m (wild type) to 98 micro m (Thr2206Met), and for caffeine from 3.8 mm to 1.8 mm. From the reduction of EC(50) we conclude that the RyR1 Thr2206Met mutation is pathogenic for MH.     

Genetic linkage for Darier disease (keratosis follicularis)

Darier disease is an autosomal dominant skin disorder characterized by abnormal keratinocyte adhesion. Recent data have provided evidence for linkage of the Darier disease locus to 12q23–24.1 in British families. We have carried out linkage analysis using the 12q markers D12S58, D12S84, D12S79, D12S86, PLA2, and D12S63 in 6 Canadian families. Pairwise linkage analysis generated positive lod scores at all 6 markers at various recombination fractions, and each family showed positive lod scores with more than one marker. The peak lod score in the multipoint analysis (Z_max) was 5.5 in the interval between markers D12S58 and D12S84. These positive lod scores in North American families of varied European ancestry confirm the location of the Darier disease gene, and suggest genetic homogeneity. The future identification and sequencing of the gene responsible for Darier disease should lead to improved understanding of the disease and of keratinocyte adhesion in general. © 1995 Wiley-Liss, Inc.     

Linkage of malignant hyperthermia and hyperkalemic periodic paralysis to the adult skeletal muscle sodium channel (SCN4A) gene in a large pedigree

Hyperkalemic periodic paralysis (HPP) is caused by mutations of the adult skeletal muscle sodium channel (SCN4A) gene on chromosome 17. Malignant hyperthermia (MH) is a genetically heterogeneous autosomal-dominant disorder occurring in association with various neuromuscular diseases or without other apparent abnormalities. In some families, MH is associated with mutations of a calcium release channel (RYR1) gene on chromosome 19. In other families, linkage of this disorder to the SCN4A gene on chromosome 17 has been suggested. We report on linkage analysis in a family in which both HPP and MH are inherited as autosomal-dominant traits. Two polymorphisms within the SCN4A locus, an RFLP and a (C-A)_n repeat, were typed on multiple family members. The findings were consistent with linkage of the polymorphic markers within the SCN4A gene to both HPP (Z_max = 6.79 at θ = 0.0) and MH (Z_max = 1.76 at θ = 0) in this family. Our data provide further evidence that MH is linked to the SCN4A locus in some families. Am. J. Med. Genet. 76:21–27, 1998. © 1998 Wiley-Liss, Inc.     

RYR mutation G1021A (Gly341Arg) is not frequent in Danish and Swedish families with malignant hyperthermia susceptibility

Malignant hyperthermia (MH) is a pharmacogenetic disorder. Susceptibility to MH (MHS) is presumed to be inherited in an autosomal dominant way. MH crises are triggered by halogenated inhalational anaesthetics and suxamethonium, and may be lethal if not treated early and adequately. Until now, eight mutations in the RYR1 gene have been described as causes of MHS phenotype in various MH families The mutation RYR1 G1021A (Gly341Arg) has been reported to account for approximately 10% of Caucasian MHS cases. However, in our study this mutation was discovered in only 1 out of 89 Scandinavian families, indicating that this mutation may be the cause of MHS in only about 1% of MHS families in those populations. The mutation may have been brought to Scandinavia by an immigrant.     

Novel missense mutations and unexpected multiple changes of RYR1 gene in 75 malignant hyperthermia families

Tammaro A, Di Martino A, Bracco A, Cozzolino S, Savoia G, Andria B, Cannavo A, Spagnuolo M, Piluso G, Aurino S, Nigro V. Novel missense mutations and unexpected multiple changes of RYR1 gene in 75 malignant hyperthermia families. Malignant hyperthermia (MH) is an autosomal dominant pharmacogenetic disorder of skeletal muscle characterized by disturbance of intracellular calcium homeostasis in the sarcoplasmic reticulum. Mutations of the ryanodine receptor 1 (RYR1) gene account for most cases, with some studies claiming up to 86% of mutations in this locus. However, RYR1 gene is large and variants are common even in the normal population. We examined 54 families with MH susceptibility and 21 diagnosed with equivocal MH. Thirty‐five were selected for an anesthetic reaction, whereas the remainder for hyperCKemia. In these, we studied all 106 exons of the RYR1 gene. When no mutation was found, we also screened: sodium channel voltage‐gated, type IV alpha subunit (SCN4A), calcium channel voltage‐dependent, L type, alpha 1S subunit (CACNA1S), and L‐type voltage‐gated calcium channel alpha 2/delta‐subunit (CACNL2A). Twenty‐nine different RYR1 mutations were discovered in 40 families. Three other MH genes were tested in negative cases. Fourteen RYR1 amino acid changes were novel, of which 12 were located outside the mutational ‘hot spots'. In two families, the known mutation p.R3903Q was also observed in malignant hyperthermia‐nonsusceptible (MHN) individuals. Unexpectedly, four changes were also found in the same family and two in another. Our study confirms that MH is genetically heterogeneous and that a consistent number of cases are not due to RYR1 mutations. The discordance between in vitro contracture test status and the presence of a proven causative RYR1 mutation suggests that the penetrance may vary due to as yet unknown factors.     

Batten disease (Spielmeyer-Sjogren disease) and haptoglobins (HP): indication of linkage and assignment to chr. 16

In a material of 26 Caucasian families, 23 with at least 2 children affected with Batten disease, we found a lod score of 3.00 at theta = 0.00 in males and theta = 0.26 in females with haptoglobin (HP), and assign the locus for Batten disease to 16q22.     

Recurrent neuroleptic malignant syndrome associated with inv dup(15) and mental retardation

Neuroleptic malignant syndrome (NMS) is an uncommon but serious adverse reaction to neuroleptic drugs. Clinically, it resembles malignant hyperthermia, a pharmacogenetic disorder of anesthesiology. Inv dup(15) is a rare but underrecognized cause of mental retardation among institutionalized patients. NMS and inv dup(15) have not been previously reported together. Their association should encourage clinicians to search for genetic markers for NMS.     

A simple method to detect the RYR1 mutation G1021A, a cause of malignant hyperthermia susceptibility

To search for the mutations RYR1 G1021A in families where malignant hyperthermia (MH) episodes have occurred, we have used an amplificationcreated restriction sites (ACRS) technique to detect the mutation. The previously described single-stranded conformation polymorphism (SSCP) technique was laborious and time consuming, but necessary to detect the mutation, whereas the method described here discriminates quickly and efficiently between homozygotes with the mutation, heterozygotes and homozygotes without the mutation.     

Mutation screening of the RYR1 gene and identification of two novel mutations in Italian malignant hyperthermia families

Point mutations in the ryanodine receptor (RYR1) gene are associated with malignant hyperthermia, an autosomal dominant disorder triggered in susceptible people (MHS) by volatile anaesthetics and depolarising skeletal muscle relaxants. To date, 17 missense point mutations have been identified in the human RYR1 gene by screening of the cDNA obtained from muscle biopsies. Here we report single strand conformation polymorphism (SSCP) screening for nine of the most frequent RYR1 mutations using genomic DNA isolated from MHS patients. In addition, the Argl63Cys mutation was analysed by restriction enzyme digestion. We analysed 57 unrelated patients and detected seven of the known RYR1 point mutations. Furthermore, we found a new mutation, Arg2454His, segregating with the MHS phenotype in a large pedigree and a novel amino acid substitution at position 2436 in another patient, indicating a 15.8% frequency of these mutations in Italian patients. A new polymorphic site in intron 16 that causes the substitution of a G at position -7 with a C residue was identified.