Malignant hyperthermia, a Scandinavian update.

BACKGROUND: Malignant Hyperthermia (MH) is a rare pharmacogenetic disorder, triggered by halogenated anesthetics and/or succinylcholine. In susceptible individuals, these drugs can activate an explosive life threatening clinical reaction. Leading symptoms are hypercarbia, muscle rigidity, and metabolic acidosis. MH is inherited in an autosomal-dominant manner and linked to mutations in the large ryanodine 1 gene (RYR1) gene in the majority of cases. Very few MH patients have been found to carry mutations in the CACNA1S gene. METHODS: For this review a large litterature search was carried out and the Swedish MH database consisting of 436 probands who have undergone in vitro muscle contraction test (IVCT) during 1984-2014 was analyzed. RESULTS: Twelve different MH causative mutations have been found in Swedish patients so far. These mutations lead to a disturbed calcium balance in striated muscle tissue. A muscle biopsy for the IVCT or finding of an approved causative mutation are required for the diagnosis. CONCLUSION: A Malignant Hyperthermia susceptible (MHS) patient should be anesthetized with trigger-free anesthesia. There are a few reports of MH-like reactions in patients unrelated to anesthesia. The outcome is dependent on early recognizing of the reaction and fast disconnection of the trigger agents and administration of dantrolene.

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.

Phenotype standardization of angioedema in the head and neck region caused by agents acting on the angiotensin system.

Angioedema is a potentially life-threatening adverse reaction to angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. To study the genetic etiology of this rare adverse event, international consortia and multicenter recruitment of patients are needed. To reduce patient heterogeneity, we have standardized the phenotype. In brief, it comprises swelling in the head and neck region that first occurs during treatment. It should not coincide with urticaria or have another likely cause such as hereditary angioedema.

Mutation screening of the RYR1-cDNA from peripheral B-lymphocytes in 15 Swedish malignant hyperthermia index cases.

BACKGROUND: Malignant hyperthermia (MH), linked to the ryanodine receptor 1 gene (RYR1) on chromosome 19, is a potentially lethal pharmacogenetic disorder which may lead to a disturbance of intracellular calcium homeostasis when susceptible individuals are exposed to halogenated anaesthetics, suxamethonium, or both. Central core disease (CCD) is a rare dominantly inherited congenital myopathy allelic to MH-susceptibility. METHODS: In this study, 14 unrelated MH-susceptible probands and one CCD patient from Sweden were screened for mutations in the RYR1. Since the RYR1 is also expressed in B-lymphocytes, RYR1-cDNA was transcribed from total RNA extracted from white blood cells. RESULTS: We detected two known RYR1 mutations and two previously described unclassified sequence variants. In addition, six novel sequence variants were detected. All mutations or sequence variants were verified on genomic DNA. Seven of the probands did not show any candidate mutation, although the total coding region of RYR1 was sequenced. Segregation data in in vitro contracture tested family members of three probands support a causative role of three of the novel sequence variants. CONCLUSIONS: Our study contributes to the genetic aetiology of MH in Sweden, but also raises questions about the involvement of genes other than RYR1 since nearly half of the probands did not show any sequence variants in the total coding region of the RYR1.

Male preponderance of patients testing positive for malignant hyperthermia susceptibility.

BACKGROUND: Malignant hyperthermia susceptibility is diagnosed using an in vitro contracture test (IVCT). In families in which the mutation is known, genetic tests are also available. The inheritance pattern is regarded as autosomal dominant, which predicts equal proportions of men and women affected. The aim of this study was to investigate whether there were sex differences in the diagnostic outcome of the 1407 patients tested for malignant hyperthermia in Sweden between 1985 and 2005. METHODS: Information about sex, diagnosis, IVCT result and kinship was analysed. Comparisons were made between the two sexes. Probands and relatives were analysed separately in order to eliminate bias caused by the type of surgery performed in the two sexes. RESULTS: Males, more than females, revealed a pathological outcome in IVCT. Amongst male relatives, the fraction of pathological outcome in IVCT was 0.70 [95% confidence interval (CI), 0.66-0.74]; the corresponding value for females was 0.40 (95% CI, 0.36-0.44). CONCLUSION: A significant difference was observed in the sex distribution of outcome of IVCT, with significantly more males revealing a pathological IVCT. This indicates the influence of one or several factors related to sex in the outcome of IVCT, for example different expression of calcium handling proteins in the sexes, a complex pattern of inheritance or unknown environmental factors.

Malignant hyperthermia and central core disease causative mutations in Swedish patients.

BACKGROUND: Malignant hyperthermia (MH) susceptibility is a pharmacogenetic disorder of intracellular calcium homeostasis. In susceptible individuals, halogenated anaesthetics and/or suxamethonium may trigger an MH reaction. The diagnosis of MH susceptibility is made by an in vitro contracture test of biopsied muscle strips. METHODS: In 27 MH susceptible (MHS) probands and four MH negative (MHN) probands, exons 17, 39, 40, 45 and 46 of the RYR1 gene were screened for MH causative mutations. In addition, in three patients with established central core disease (CCD), exons 17, 39, 40, 45 and 46 and exons 95, 100, 101 and 102 were screened for MH and CCD causative mutations. All screenings were performed by direct sequencing of the entire exons. RESULTS: MH causative mutations were found in five of the 27 MHS probands (19%). CCD causative mutations were found in two of three CCD patients in the C-terminal exons. None of the CCD patients showed a mutation in N-terminal exon 17 or in the central exons. CONCLUSIONS: In a Swedish population, screening of N-terminal exon 17 and the central exons for MH causative mutations in the RYR1 gene covers 19% of families. Thus, other mutations must also be responsible for MH susceptibility in Sweden. Although the number of CCD patients in this study was small, screening of the C-terminal exons for CCD causative mutations seems to be a promising tool in the process of making a diagnosis.

Reproducibility of in vitro contracture test results in patients tested for malignant hyperthermia susceptibility.

BACKGROUND: The in vitro contracture test (IVCT) is the golden standard to diagnose malignant hyperthermia susceptibility (MHS). A high reproducibility is important for a high validity of a test. METHODS: We have therefore analyzed IVCT in 838 patients, investigated in two laboratories. Each halothane and caffeine test was performed in two muscle strips. The test results were analyzed with respect to reproducibility of abnormal outcomes within pairs of tested muscle strips and size of contractures, thresholds and quality criteria. The patients were tested according to the European Malignant Hyperthermia Group protocol (EMHG). To fulfill quality criteria in the EMHG protocol the twitch height should be 10 mN (1 g) or more. For the caffeine test a minimum contracture of 50 mN (5 g) or more at 32 mmol l-1 caffeine could be used as an alternative quality criterion. RESULTS: There was better reproducibility with larger contractures. The correlation between size of contractures and fraction of muscle strips with abnormal contractures was 0.77 or larger. Contractures < 5 mN (0.5 g) were reproducible in less than half of the tests. There was no difference in reproducibility or size of contractures between tests fulfillling all quality criteria and those not fulfillling these criteria. CONCLUSIONS: IVCT responses close to cut off limits, i.e. <5 mN (0.5 g) in the EMHG protocol, are less reproducible and must scientifically be considered as less reliable. The clinical cut off limits must remain unchanged for reasons of clinical safety. The outcome of quality measurements does not influence the test results.

Between-center variability of results of the in vitro contracture test for malignant hyperthermia susceptibility.

UNLABELLED: The in vitro contracture test (IVCT) remains the standard test for the diagnosis of malignant hyperthermia (MH) susceptibility. The aim of this study was to investigate whether results of the IVCT varied between two diagnostic centers. The study took place at the national MH centers in Denmark and Sweden. Forty-three patients investigated for MH gave informed consent to have four extra muscle specimens excised. These were sent to the other center and immediately used for a parallel IVCT, according to the protocol of the European MH Group. Results of the IVCTs performed in the two centers on muscle samples from the same patients were compared. Each patient was assigned a diagnosis according to the result obtained in the "mother-center." Identical diagnostic results were obtained for 56% of the patients. The differing diagnostic outcomes were almost exclusively seen in cases with contractures of <5 mN (0.5 g) and abnormal results in only one or two muscle strips. We suggest different criteria for the interpretation of results for clinical and scientific purposes. The clinical criteria should remain unchanged. The scientific designation of susceptibility should be used in cases with contractures of > or =5 mN and abnormal results in at least 75% of the tested muscle strips. IMPLICATIONS: The diagnostic outcomes of tests for malignant hyperthermia susceptibility were compared between two laboratories by using muscle tissue from the same patients. Identical outcomes were found for 56% of the patients. Almost all diverging outcomes were seen in cases with a few small contractures near the cutoff limit. Different diagnostic criteria for clinical and scientific purposes are suggested.

Severe neuroexcitatory symptoms after anaesthesia--with focus on propofol anaesthesia.

Delayed neuroexcitatory symptoms after an uneventful anaesthesia are uncommon, although described in many reports. We want to report on two cases. The first patient developed muscle hypertonicity, jerky movements and unconsciousness after an uneventful anaesthesia with propofol, and later the same thing happened after anaesthesia with thiopentone. The second patient developed similar symptoms after an uneventful anaesthesia with propofol, but she never recovered completely after this and is now severely disabled. A search of the literature and the Swedish adverse drug reactions register revealed many similar cases. In both our patients the causal relationship between propofol and the neuroexcitatory symptoms remains uncertain, but we want to alert readers about this possible adverse reaction.

Comparison between the European and North American protocols for diagnosis of malignant hyperthermia susceptibility in humans.

UNLABELLED: We compared the diagnostic outcome of in vitro contracture tests for diagnosis of malignant hyperthermia susceptibility performed according to the European Malignant Hyperthermia Group protocol and the North American Malignant Hyperthermia Group protocol. The aim of the study was to compare the two major diagnostic tests of malignant hyperthermia susceptibility to have basic data for a common worldwide protocol. We evaluated 156 patients and 17 control individuals. The accordance in diagnostic outcome was 87%. The diverging outcomes between the two protocols were found in a group of patients reacting in few muscle strips and close to the cutoff limits. A 100% accordance in diagnostic outcome was found in individuals with contractures in at least five of six tested muscle strips. In both protocols, contractures close to the cutoff limits in a few muscle strips in scientific studies should be considered as unknown results. IMPLICATIONS: We compared the two major protocols for investigating malignant hyperthermia susceptibility. There was 87% accordance in diagnostic outcome. The diverging outcomes were seen in individuals with less reproducible test results near the cutoff limits. In scientific studies, such results should be considered as unknown.

Malignant hyperthermia susceptibility, an autosomal dominant disorder?

A large series of Swedish nuclear families, in which malignant hyperthermia (MH) reactions had occurred during anaesthesia, have been examined with respect to malignant hyperthermia susceptibility. In vitro contracture tests (IVCT) of muscle strips were conducted to diagnose MH status. Included in this series were some families where only one of the parents was tested by IVCT, while in 79 of the families both parents were tested by IVCT. Six known mutations in the gene encoding the calcium release channel of sarcoplasmic reticulum in skeletal muscle (the RYR1 gene), believed to cause MHS in man, were searched for in 41 nuclear families. The present paper focuses on findings in eight families, where both parents were malignant hyperthemia negative (MHN), while at least one child was either malignant hyperthermia susceptible (MHS) or malignant hyperthermia equivocal (MHE). There was no suggestion of non-paternity. The RYR1 mutations investigated were Arg163Cys, Gly341Arg, Ile403Met, Arg614Cys, Gly2433Arg and Arg2434His. No family had any of the six RYR1 mutations searched for.

Results of in vitro contracture tests for the diagnosis of malignant hyperthermia susceptibility in monozygote twins.

BACKGROUND: Malignant hyperthermia susceptibility is a pharmacogenetic disorder in which susceptible individuals may develop a potentially life-threatening hypermetabolism when exposed to certain anaesthetic agents. The most common diagnostic method is the in vitro contracture test (IVCT) of skeletal muscle biopsies. There is a wide variation in the size of contractures between susceptible individuals and the reproducibility of the test in humans has not been evaluated. METHODS: We have performed the IVCT in 4 monozygote pairs of twins, which gave us on opportunity to study the reproducibility. RESULTS: The clinical diagnoses were consistent in all twin pairs, although slight differences in contractures and thresholds were seen. CONCLUSION: In this material the reproducibility of the IVCT was found to be satisfactory.

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.

Recombination between the postulated CCD/MHE/MHS locus and RYR1 gene markers.

Malignant hyperthermia (MH) susceptibility is considered a subclinical myopathy or a pharmacogenetic trait, and is believed to be closely associated with central core disease (CCD). Data support the notion that MH susceptibility is heterogeneous, with the ryanodine receptor I (RYR1) locus on chromosome 19 being one locus harboring a gene that can cause MH susceptibility. The gene for CCD is believed to reside in the locus on chromosome 19. In the family presented here, a girl has CCD, and several close relatives are MH susceptible (MHS). DNA studies conducted on available family members uncovered recombination between the MH susceptibility locus and RYR1 markers. Consequently, if one postulates that the CCD gene in this family resides in the same locus as the MH susceptibility gene, an additional CCD locus different from the RYR1 locus must also be postulated.

Results of in vitro contracture testing of both parents of malignant hyperthermia susceptible probands.

BACKGROUND: Malignant Hyperthermia (MH) is regarded as a dominantly inherited condition. Therefore, most investigators do not test the second parent if the first parent is found to be MH susceptible (MHS). The purpose of this study was to validate this policy. METHODS: In vitro contracture tests (IVCT) have been performed in both parents of 101 MH susceptible probands. Diagnoses were made according to the European MH group protocol and include MH susceptible (MHS), MH equivocal (MHE) and MH negative (MHN). Our control material consists of 60 patients without any personal or family history of MH. RESULTS: Thirty-seven pairs of parents were MHS-MHN, 20 were MHE-MHN, 6 were MHS-MHS, 20 were MHS-MHE, 6 were MHE-MHE, and 12 were MHN-MHN. The frequency of MHE was greater in the parents than in the controls (26% versus 8%, P < 0.05). Several possible explanations exist: the IVCT produces false positive and/or false negative results; the MH genes may be more frequent in the population than previously expected; MH susceptibility may have more than one mode of inheritance; the mutation rate may not be negligible. Our test results in controls and fulminants point at a combination of these explanations. CONCLUSIONS: We conclude that both parents should be tested whenever possible. For genetic research it is important that labelling any parent "presumed normal" may give misleading results.

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.

Evaluation of anaesthesias in malignant hyperthermia negative patients.

In vitro contracture test is still the most reliable method for diagnosing malignant hyperthermia susceptibility. In order to investigate the reliability of Malignant Hyperthermia Negative (MHN) results, a questionnaire was sent to 237 persons of whom 133 were consecutively investigated and found to be MHN, together with 104 of their children. In 17 anaesthetics with triggering agents in 7 MHN patients and 7 children of MHN patients, no signs of malignant hyperthermia were observed in any patient. This material is, however, too small to draw any conclusion about the reliability of MHN test results. This can only be done in a large multicentre study or a metaanalysis of several studies.

A search for three known RYR1 gene mutations in 41 Swedish families with predisposition to malignant hyperthermia.

Eight mutations in the gene (the RYR1 gene) encoding the calcium release channel of sarcoplasmic reticulum (SR) in skeletal muscle are so far known to be very closely linked to malignant hyperthermia susceptibility in man and are regarded to be causative. We have examined 41 Swedish families where malignant hyperthermia had occurred in at least one member during anaesthesia, with respect to three of the known mutations. The mutations were Arg163Cys; Ile403Met and Arg614Cys (also known as the "pig mutation"). In three (i.e. 7%) of the families we detected the Arg614Cys mutation, and this was the only one of the mutations searched for that was observed. This indicates that other mutations than those searched for in this study must cause malignant hyperthermia susceptibility in most Swedish malignant hyperthermia susceptible families.

Malignant hyperthermia susceptibility without central core disease (CCD) in a family where CCD is diagnosed.

Central Core Disease (CCD) is a myopathy closely linked to malignant hyperthermia (MH) susceptibility. We present a family with a girl suffering from CCD. Due to the CCD diagnosis, all available relatives were investigated for MH-susceptibility. No other family member has CCD. In vitro contracture tests revealed that several relatives are MH-susceptible. Thus our results suggest that healthy members of families with CCD could be at risk for being malignant hyperthermia susceptible.