Genome-wide association study of angioedema induced by angiotensin-converting enzyme inhibitor and angiotensin receptor blocker treatment

Angioedema in the mouth or upper airways is a feared adverse reaction to angiotensin-converting enzyme inhibitor (ACEi) and angiotensin receptor blocker (ARB) treatment, which is used for hypertension, heart failure and diabetes complications. This candidate gene and genome-wide association study aimed to identify genetic variants predisposing to angioedema induced by these drugs. The discovery cohort consisted of 173 cases and 4890 controls recruited in Sweden. In the candidate gene analysis, ETV6, BDKRB2, MME, and PRKCQ were nominally associated with angioedema (p < 0.05), but did not pass Bonferroni correction for multiple testing (p < 2.89 × 10−5). In the genome-wide analysis, intronic variants in the calcium-activated potassium channel subunit alpha-1 (KCNMA1) gene on chromosome 10 were significantly associated with angioedema (p < 5 × 10−8). Whilst the top KCNMA1 hit was not significant in the replication cohort (413 cases and 599 ACEi-exposed controls from the US and Northern Europe), a meta-analysis of the replication and discovery cohorts (in total 586 cases and 1944 ACEi-exposed controls) revealed that each variant allele increased the odds of experiencing angioedema 1.62 times (95% confidence interval 1.05–2.50, p = 0.030). Associated KCNMA1 variants are not known to be functional, but are in linkage disequilibrium with variants in transcription factor binding sites active in relevant tissues. In summary, our data suggest that common variation in KCNMA1 is associated with risk of angioedema induced by ACEi or ARB treatment. Future whole exome or genome sequencing studies will show whether rare variants in KCNMA1 or other genes contribute to the risk of ACEi- and ARB-induced angioedema

In vitro contracture testing for the diagnosis of malignant hyperthermia susceptibility

Malignant hyperthermia (MH) susceptibility is a rare inherited muscular disorder, which may cause a lethal increase in metabolism during anaesthesia with certain commonly used anaesthetic. Susceptible individuals are without any signs or symptoms. It is important to identify individuals at risk, since the MH reaction is preventable. Susceptibility to MH is diagnosed with an in vitro contracture test (IVCT) performed on viable skeletal muscle. The muscle is exposed to halothane/caffeine in an organ bath. An increase in baseline tension >=0.2g is abnormal. There have been few thorough validations of the IVCT and false diagnoses do occur, which make genetic research difficult. We have investigated 1) the reliability of a negative diagnosis, 2) the inheritance pattern suggested by IVCT and 3) the validation the IVCT results in 706 patients in 175 families. Fourteen patients diagnosed MH negative revealed no signs of MH when exposed to anaesthetics known to cause MH. Judged from outcome of IVCT in 101 families, there is more than one mode of inheritance. The IVCT was validated with comparisons within and between laboratories, between different types of tests and within and between monozygotic twins. We found that increase in baseline tension exceeding 0.5g were almost always reproducible within and between laboratories, between different types of tests and within and between monozygotic twins. Our conclusions are that 1. There are no indications of false negative diagnoses. 2. There could be more than one mode of inheritance. 3. For scientific purposes when a high specificity is needed the threshold could be increased to 0.5g. However the clinical diagnostic cut off limits should be unchanged

Male preponderance of patients testing positive for malignant hyperthermia susceptibility.

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

A family with discordance between malignant hyperthermia susceptibility and rippling muscle disease

Rippling muscle disease (RMD) is a disorder that affects striated muscle and involves disturbances in calcium homeostasis. Malignant hyperthermia susceptibility (MHS) is a potentially lethal disorder, characterized by extreme hypermetabolism and muscle rigidity/rhabdomyolysis during anesthesia with potent inhalational agents, in otherwise healthy individuals. The aim of this report was to search for a correlation between RMD and MHS in members of a family in which both disorders were present. Ten members of a large Swedish family segregating RMD were tested for MHS prior to establishing an RMD diagnosis. Results from diagnostic RMD investigations and anesthesia outcomes were collected and cross-referenced to evaluate whether phenotype variations could be predicted by in vitro contracture test (IVCT) results suggestive of MHS. No correlation was found between individual RMD phenotypes and the IVCT results. There were no recorded adverse reactions to anesthesia, and RMD and MHS did not co-segregate. We conclude that RMD patients should not, on the basis of our present knowledge, be classified as having MHS; however, an increased surveillance for MH reactions is recommended in these patients

Functional properties of RYR1 mutations identified in Swedish patients with malignant hyperthermia and central core disease

BACKGROUND: A diagnosis of malignant hyperthermia susceptibility by in vitro contraction testing can often only be performed at specialized laboratories far away from where patients live. Therefore, we have designed a protocol for genetic screening of the RYR1-cDNA and for functional testing of newly identified ryanodine receptor 1 (RYR1) gene variants in B lymphocytes isolated from peripheral blood samples drawn at local primary care centers. METHODS: B lymphocytes were isolated for the extraction of RYR1-mRNA and genomic DNA and for establishment of lymphoblastoid B cell lines in 5 patients carrying yet unclassified mutations in the RYR1. The B lymphoblastoid cell lines were used to study resting cytoplasmic calcium concentration, the peak calcium transient induced by the sarco(endo)plasmic reticulum Ca-ATPase inhibitor thapsigargin, and the dose-dependent calcium release induced by the ryanodine receptor agonist 4-chloro-m-cresol. RESULTS: It was possible to extract mRNA for cDNA synthesis and to create B lymphocyte clones from all samples. All B lymphoblastoid cell lines carrying RYR1 candidate mutations showed significantly increased resting cytoplasmic calcium levels as well as a shift to lower concentrations of 4-chloro-m-cresol inducing calcium release compared with controls. CONCLUSIONS: Peripheral blood samples are stable regarding RNA and DNA extraction and establishment of lymphoblastoid B cell lines after transportation at ambient temperature over large distances by ordinary mail. Functional tests on B cells harboring the newly identified amino acid substitutions indicate that they alter intracellular Ca2+ homeostasis and are most likely causative of malignant hyperthermia

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

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