Identification of a novel mutation in the ryanodine receptor gene (RYR1) in a malignant hyperthermia Italian family.

Malignant hyperthermia (MH) is an inherited autosomal dominant pharmacogenetic disorder and is one of the main causes of death subsequent to anaesthesia. Around 50% of affected families are linked to the ryanodine receptor (RYR1) gene. To date, 19 mutations have been identified in the coding region of this gene and appear to be associated with the MH-susceptible phenotype. Here we report the identification by two independent methods of a novel mutation associated with the MH-susceptible phenotype in the RYR1 gene: the 6488G-->C transversion, resulting in the replacement of the Arg2163 with a proline residue.

A case of discordance between genotype and phenotype in a malignant hyperthermia family.

Malignant hyperthermia (MH) is an inherited autosomal dominant pharmacogenetic disorder and is the major cause of anaesthesia-induced death. Malignant hyperthermia susceptibility is usually diagnosed by the in vitro contracture test (IVCT) performed on fresh muscle biopsies exposed to caffeine and halothane, respectively. Around 50% of affected families are linked to the ryanodine receptor (RYR1) gene. The human RYR1 gene maps to chromosome 19q13.1 and encodes a protein that associates as a homotetramer and acts as a calcium-release channel from the sarcoplasmic reticulum. To date, 17 mutations have been identified in the coding region of the RYR1 gene and appear to be associated to the MH-susceptible phenotype. Here we describe a rare case of discordance between genotype (characterised by the presence of the Arg614Cys mutation in the RYR1 gene) and MH-normal typed phenotype. Although the IVCT remains a very reliable procedure for the assessment of MH status, genetic data can provide in some cases an additional aid to clinical diagnosis.

Recent advances in the diagnosis of malignant hyperthermia susceptibility: how confident can we be of genetic testing?

Malignant hyperthermia (MH) is a condition that manifests in susceptible individuals only on exposure to certain anaesthetic agents. Although genetically heterogeneous, mutations in the RYR1 gene (19q13.1) are associated with the majority of reported MH cases. Guidelines for the genetic diagnosis for MH susceptibility have recently been introduced by the European MH Group (EMHG). These are designed to supplement the muscle biopsy testing procedure, the in vitro contracture test (IVCT), which has been the only means of patient screening for the last 30 years and which remains the method for definitive diagnosis in suspected probands. Discordance observed in some families between IVCT phenotype and susceptibility locus genotype could limit the confidence in genetic diagnosis. We have therefore assessed the prevalence of 15 RYR1 mutations currently used in the genetic diagnosis of MH in a sample of over 500 unrelated European MH susceptible individuals and have recorded the frequency of RYR1 genotype/IVCT phenotype discordance. RYR1 mutations were detected in up to approximately 30% of families investigated. Phenotype/genotype discordance in a single individual was observed in 10 out of 196 mutation-positive families. In five families a mutation-positive/IVCT-negative individual was observed, and in the other five families a mutation-negative/IVCT-positive individual was observed. These data represent the most comprehensive assessment of RYR1 mutation prevalence and genotype/phenotype correlation analysis and highlight the possible limitations of MH screening methods. The implications for genetic diagnosis are discussed.

Minimal flow and half-closed system ventilation in lung surgery.

BACKGROUND: This study aimed at determining the applicability of minimal flow anaesthesia in lung surgery. METHODS: The standards anaesthesiological technique was modified to perform minimal flow half-closed system ventilation. For procedures on left lung orobronchial intubation was performed by a White no. 41 and no. 39 orotracheal tube, respectively in male and in female patients, in order to achieve a perfect tight of bronchial cuff and prevent gas loss from the circuit, because of the greater calibre of the right stem bronchus. The metal double lumen connector was replaced by a plastic tube that is clamped to exclude the lung from ventilation, whenever necessary. Fibrin glue was systematically applied on the bronchial stump or resected lung tissue before restoring ventilation. RESULTS: No significant changes were recorded in heart rate, arterial systolic and diastolic pressure, end-expiratoy CO2 concentration, oxygen saturation, airways maximum and minimum pressure. CONCLUSIONS: Minimal flow half-closed system ventilation can be easily performed also in pulmonary surgery provided that gas loss from the circuit is 50 ml/min by means of specific technical adjustments.

In vitro contracture test for diagnosis of malignant hyperthermia following the protocol of the European MH Group: results of testing patients surviving fulminant MH and unrelated low-risk subjects. The European Malignant Hyperthermia Group.

BACKGROUND: Determination of sensitivity and specificity of the in vitro contracture test (IVCT) for malignant hyperthermia (MH) susceptibility using the European MH Group (EMHG) protocol has been performed in some laboratories but only on a small sample from the combined EMHG. Thus, the purpose of the present study was to determine combined EMHG sensitivity and specificity of the test. METHODS: Results of IVCT of patients with previous fulminant MH and normal, low-risk subjects (controls) were collected from 22 centres of the EMHG. IVCT was performed according to the EMHG protocol. Patients were included in the study if the clinical crisis had a score of at least 50 points with the Clinical Grading Scale. Low-risk subjects were included provided they did not belong to a family with known MH susceptibility, they had not developed any signs of MH at previous anaesthetics, and they did not suffer from any neuromuscular disease. For inclusion of both MH patients and low-risk subjects, at least 1 muscle bundle in the IVCT should have twitches of 10 mN (1 g) or more. For evaluation of individual tests, only muscle bundles with twitch heights of 10 mN (1 g) or more were used. RESULTS: A total of 1502 probands had undergone IVCT because of a previous anaesthesia with symptoms and signs suggestive of MH. Of these, 119 had clinical scores of 50 and above. From these 119 MH-suspected patients and from 202 low-risk subjects, IVCT data were collected. Subsequently, 14 MH-suspected patients were excluded from further analysis for the following reasons: In 3 patients, the suspected MH episode could be fully explained by diseases other than MH; in 11 MHS patients, IVCT was incomplete (n = 1), data were lost (n = 3), or none of the muscle bundles fulfilled twitch criteria (n = 7). Of the remaining 105 MH-suspected patients, 89 were MHS, 10 MHEh, 5 MHEc, and one MHN. Thus, we observed a diagnostic sensitivity of the IVCT of 99.0% if the MHE group is considered susceptible (95% confidence interval 94.8-100.0%). Of the 202 low-risk subjects, 3 were MHS, 5 MHEh, 5 MHEc, and 189 MHN. This gives a specificity of the IVCT of 93.6% (95% confidence interval 89.2-96.5%). CONCLUSION: The IVCT for diagnosis of MH susceptibility in Europe has a high sensitivity and a satisfactory specificity.