Malignant hyperthermia and central core disease causative mutations in Swedish patients

Masseter muscle rigidity and the role of DNA analysis to confirm malignant hyperthermia susceptibility

Malignant hyperthermia (MH) is an uncommon, autosomal dominant disorder of skeletal muscle, triggered by inhalational anaesthetics or depolarizing muscle relaxants. Masseter muscle rigidity (MMR) can be regarded as potentially a preceding sign for an MH reaction. Susceptibility to MH can be determined by the in vitro contracture test (IVCT) or DNA analysis where a familial variant is known. Our aims were to review patients with MMR, where IVCT and DNA analysis had been undertaken, to determine if DNA analysis could be used as an initial screening tool for MH susceptibility, and, by reviewing standard monitored variables (SMVs), to determine if any clinical characteristics could be used to differentiate between MMR patients who are MH susceptible (MHS) and those who are not. Patients with MMR were identified from the Palmerston North Hospital MH Reactions Database. IVCT and DNA analysis results were documented. DNA testing was performed retrospectively in the majority of patients as many patients had presented before DNA analysis was available. Forty-one patients were analysed. Fourteen were DNA positive/IVCT positive and six DNA positive only (48% in total), seven were IVCT positive/DNA negative and 14 were IVCT normal. Increased creatine kinase (>18,000 units/L) was consistent with MH susceptibility. Severity of MMR was not linked to MH susceptibility. This study confirmed that DNA analysis can be used as a first-line test for MH susceptibility in patients presenting with MMR (consistent with European MH Group recommendations). Creatine kinase was the only SMV that was significantly different between MHS and MH normal individuals.

Clinical and Pathologic Findings of Korean Patients with RYR1-Related Congenital Myopathy

Background and Purpose

This study was designed to investigate clinical and pathologic characteristics of five Korean patients with RYR1-related congenital myopathy (CM).

Methods

Five patients from unrelated families were diagnosed with RYR1-related CM via direct or targeted sequencing of RYR1. Their clinical, mutational, and pathologic findings were then analyzed.

Results

Seven different mutations were identified, including two novel mutations: c.5915A>T and c.12250C>T. All of the patients presented at infancy with proximal dominant weakness and delayed motor milestones. Other clinical findings were scoliosis in three patients, winged scapula in two, hip dislocation in one, and pectus excavatum in one. Ophthalmoplegia was observed in one patient with a novel recessive mutation. Two of three muscle specimens revealed a myopathic pattern with core.

Conclusions

We have identified a novel compound heterozygous RYR1 mutation and demonstrated clinical and pathologic findings in five Korean patients with RYR1-related CM.

Evidence of Malignant Hyperthermia in Patients Administered Triggering Agents before Malignant Hyperthermia Susceptibility Identified: Missed Opportunities Prior to Diagnosis

Malignant hyperthermia (MH) is a hypermetabolic disorder of skeletal muscle triggered almost exclusively by potent inhalational agents and suxamethonium. Signs of an MH reaction are non-specific and may be confused with the presentation of other problems such as sepsis and overheating of a patient. A high index of suspicion is needed to be aware of an early presentation of MH. Nine patients are presented who showed abnormal signs with an earlier anaesthetic where the possible diagnosis of an MH reaction was missed. These patients either presented later with an MH reaction, confirmed by DNA analysis and in some cases in vitro contracture testing, or were diagnosed by the identification of a causative mutation confirming MH susceptibility. The MH clinical grading scale is helpful in determining the likelihood that clinical indicators indicate a possible MH reaction. Masseter muscle rigidity is a known sign of MH, confirmed in this report by positive in vitro contracture testing and DNA analysis. Several uncommon muscle disorders have a high association with MH, and postoperative myalgia unrelated to suxamethonium can be a sign which is associated with MH. These reports emphasise the importance of a thorough family history (as the MH status was known by the family in four patients), a high index of suspicion for MH, and documentation of the possibility of MH susceptibility in the anaesthesia record.

Functional characterization of the RYR1 mutation p.Arg4737Trp associated with susceptibility to malignant hyperthermia

Aside from the in vitro contracture test, genetic screening for causative RYR1 mutations is the established procedure to diagnose susceptibility to malignant hyperthermia (MH). However, currently only 34 out of more than 300 known RYR1 mutations have been confirmed to be causative for MH by experimental studies addressing their functional impact on intracellular calcium homeostasis. The RYR1 mutation p.Arg4737Trp has been recently detected in a German MH family. To evaluate the effects of that mutation on intracellular calcium handling, the response after stimulation with the RYR1 agonist 4-chloro-m-cresol was investigated in immortalized B lymphocytes containing the p.Arg4737Trp mutation and compared to the response of wild type RYR1 from unaffected family members and unrelated controls. Intracellular resting calcium was slightly but significantly elevated in mutation positive cells. Calcium release following stimulation with 4-chloro-m-cresol was significantly increased in B lymphocytes carrying the p.Arg4737Trp mutation compared to mutation negative controls. Hence, the functional properties of the RYR1 mutation p.Arg4737Trp are consistent with susceptibility to MH. Together with previously published data, the mutation has now been reported in three independent MH positive families.

Malignant hyperthermia: a review

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that presents as a hypermetabolic response to potent volatile anesthetic gases such as halothane, sevoflurane, desflurane, isoflurane and the depolarizing muscle relaxant succinylcholine, and rarely, in humans, to stressors such as vigorous exercise and heat. The incidence of MH reactions ranges from 1:10,000 to 1: 250,000 anesthetics. However, the prevalence of the genetic abnormalities may be as great as one in 400 individuals. MH affects humans, certain pig breeds, dogs and horses. The classic signs of MH include hyperthermia, tachycardia, tachypnea, increased carbon dioxide production, increased oxygen consumption, acidosis, hyperkalaemia, muscle rigidity, and rhabdomyolysis, all related to a hypermetabolic response. The syndrome is likely to be fatal if untreated. An increase in end-tidal carbon dioxide despite increased minute ventilation provides an early diagnostic clue. In humans the syndrome is inherited in an autosomal dominant pattern, while in pigs it is autosomal recessive. Uncontrolled rise of myoplasmic calcium, which activates biochemical processes related to muscle activation leads to the pathophysiologic changes. In most cases, the syndrome is caused by a defect in the ryanodine receptor. Over 400 variants have been identified in the RYR1 gene located on chromosome 19q13.1, and at least 34 are causal for MH. Less than 1 % of variants have been found in CACNA1S but not all of these are causal. Diagnostic testing involves the in vitro contracture response of biopsied muscle to halothane, caffeine, and in some centres ryanodine and 4-chloro-m-cresol. Elucidation of the genetic changes has led to the introduction of DNA testing for susceptibility to MH. Dantrolene sodium is a specific antagonist and should be available wherever general anesthesia is administered. Increased understanding of the clinical manifestation and pathophysiology of the syndrome, has lead to the mortality decreasing from 80 % thirty years ago to <5 % in 2006.

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.

Congenital myopathies

PURPOSE OF REVIEW

The present review aims to discuss the pathological and clinical heterogeneity of congenital myopathies, and the overlap between the different variants highlighted by recent studies.

RECENT FINDINGS

The spectrum of pathological changes associated with known gene defects has widened, and new genes responsible for rare structural defects have been identified. The complexity of the classification of these conditions is highlighted by the realization that defects in the same gene can result in diverse phenotypes, including disorders traditionally classified as congenital myopathies with structural abnormalities, adult-onset disorders, conditions characterized by distal weakness and wasting, or distal arthrogryposis. There is a wider appreciation of the complexities of inheritance and of the value of noninvasive assessment, such as muscle MRI. New animal models provide a better understanding of pathogenesis and are highlighting therapeutic possibilities.

SUMMARY

The overlap of clinical and pathological features in the congenital myopathies has led to the recognition that diverse disorders are often associated with the same causative gene, and is challenging traditional classifications. Identification of further causative genes and development of new models will further the understanding of pathogenesis and development of therapies.

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.