Pharmacogenomics and acquired long QT syndrome

During the past decade pharmaceutical companies have been faced with the withdrawal of some of their marketed drugs because of rare, yet lethal, postmarketing reports associated with ventricular arrhythmias. The implicated drugs include antiarrhythmics, but also non-cardiac drugs, such as histamine blockers, antipsychotics, and antibiotics. These undesired effects involve prolongation of the QT interval, which may lead to characteristic ventricular tachyarrhythmias, known as torsades de pointes. These clinical symptoms of the acquired long QT syndrome (LQTS) are also found in an inherited form of the disease, called congenital LQTS. Nowadays, a number of environmental (non-genetic) and genetic risk factors for acquired LQTS have been described. Non-genetic factors include female gender, hypokalemia, and other heart diseases. The knowledge of genetic risk factors is emerging rapidly. During the last decade, mutations in several genes encoding ion channels have been shown to cause congenital LQTS. In acquired LQTS, a number of 'silent' mutation carriers in these LQTS genes have been identified, and functional polymorphisms in the same genes have been found that are associated with an increased vulnerability for the disease. Furthermore, there is also evidence that interindividual differences in drug metabolism, caused by functional polymorphisms in drug-metabolizing enzyme genes, may be a risk factor for acquired LQTS, especially if multiple drugs are involved. This review evaluates the current knowledge on these risk factors for acquired LQTS, with an emphasis on the genetic risk factors. It also assesses the potential to develop pharmacogenetic tests that will enable clinicians and pharmaceutical companies to identify at an early stage patients or individuals in the general population who are at risk of acquired LQTS

Genetic basis of drug-induced arrhythmias

Genetic basis of drug-induced arrhythmias. Vos MA, Paulussen AD. Department of Medical Physiology, University Medical Center Utrecht, The Netherlands. [email protected] Drug-induced torsade de pointes arrhythmia (TdP) is frequently seen in patients. This proarrhythmia is not restricted to anti-arrhythmics but includes a variety of drugs. A genetic predisposition is an attractive explanation for this clinical problem. In this review, we: 1) explain the arrhythmogenic mechanisms of TdP, 2) provide data for a genetic cause based upon mutations in the long QT or in cytochrome genes responsible for drug metabolism, and 3) present pathology-based electrical remodeling as an alternative explanation. It can be concluded that the current evidence for a genetic basis for drug-induced TdP is wea

Mutation analysis in congenital Long QT Syndrome--a case with missense mutations in KCNQ1 and SCN5A

Mutation analysis in congenital Long QT Syndrome--a case with missense mutations in KCNQ1 and SCN5A. Paulussen A, Matthijs G, Gewillig M, Verhasselt P, Cohen N, Aerssens J. Department of Pharmacogenomics, Johnson & Johnson Pharmaceutical Research and Development, Beerse, Belgium. Long QT Syndrome (LQTS) is a cardiac disease characterized by a prolonged QT interval on a surface electrocardiogram (ECG) and by clinical symptoms such as seizures, syncope, and cardiac sudden death. At present, causal mutations of LQTS have been identified in five cardiac ion-channel genes. Because a causal mutation is usually unique to a specific family and can be located in any region of any of these five genes, a mutation analysis effort may require screening of the complete coding regions of each of these genes. The causative nature of a detected mutation can then be determined either by family history or by functional studies, such as the electrophysiological signature of the mutation. Here we describe a mutation analysis of an LQTS patient who carries two heterozygous missense mutations in two different LQTS genes. The first mutation identified, A572D in SCN5A, was not linked with clinical LQTS features in the two other mutation carriers in the family; neither was it identified in 90 healthy controls. Therefore, this mutation most likely has either a mild effect on cardiac ion-channel function or represents a very rare polymorphism. The second mutation, V254M in KCNQ1, co-segregated with higher QT intervals and symptoms in other family members, and was previously reported in another LQTS family. Because the clinical LQTS symptoms are most pronounced in the proband, a combined effect of both mutations cannot be excluded, although no functional data are available to support such an hypothesis. We conclude that, for newly presented LQTS cases, a mutation analysis strategy should routinely screen the complete coding regio

A novel mutation (T65P) in the PAS domain of the human potassium channel HERG results in the long QT syndrome by trafficking deficiency

A novel mutation (T65P) in the PAS domain of the human potassium channel HERG results in the long QT syndrome by trafficking deficiency. Paulussen A, Raes A, Matthijs G, Snyders DJ, Cohen N, Aerssens J. Department of Pharmacogenomics, Johnson & Johnson Pharmaceutical Research and Development, Beerse B-2340, Belgium. [email protected] The congenital long QT syndrome is a cardiac disease characterized by an increased susceptibility to ventricular arrhythmias. The clinical hallmark is a prolongation of the QT interval, which reflects a delay in repolarization caused by mutations in cardiac ion channel genes. Mutations in the HERG (human ether-a-go-go-related gene KCNH2 can cause a reduction in I(Kr), one of the currents responsible for cardiac repolarization. We describe the identification and characterization of a novel missense mutation T65P in the PAS (Per-Arnt-Sim) domain of HERG, resulting in defective trafficking of the protein to the cell membrane. Defective folding of the mutant protein could be restored by decreased cell incubation temperature and pharmacologically by cisapride and E-4031. When trafficking was restored by growing cells at 27 degrees C, the kinetics of the mutated channel resembled that of wild-type channels although the rate of activation, deactivation, and recovery from inactivation were accelerated. No positive evidence for the formation of heterotetramers was obtained by co-expression of wild-type with mutant subunits at 37 degrees C. As a consequence the clinical symptoms may be explained rather by haploinsufficiency than by dominant negative effects. This study is the first to relate a PAS domain mutation in HERG to a trafficking deficiency at body temperature, apart from effects on channel deactivatio

Two functionally relevant polymorphisms in the human progesterone receptor gene (+331 G/A and progins) and the predisposition for breast and/or ovarian cancer

OBJECTIVE.: Two polymorphisms affecting either expression (+331 G/A) or transcriptional activity (progins) of the progesterone receptor have been described. No clear correlation between either polymorphism and breast or ovarian cancer has been shown. Our objective is to clarify whether the two progesterone receptor polymorphisms modify the risk for breast or ovarian cancer. METHODS.: Healthy women and women suffering from either ovarian or breast cancer were enrolled in a case-control-based study to compare the frequencies of women carrying either one, both or none of the two polymorphisms. Patient and control populations resided in the same region of South Germany. PCR-RFLP analysis was used to determine the polymorphic alleles. RESULTS.: Women diagnosed with ovarian cancer showed a not significant increased frequency of +331 A carriers and a significantly increased frequency of progins carriers. Both polymorphisms appeared to be associated with a significantly increased risk for the disease in women below 51 years [OR: 4.1 (CI: 1.2-13.9) and 3.2 (CI: 1.1-9.1), respectively]. No association was detected between either of the two polymorphisms and breast cancer. Among ovarian and breast cancer patients, the number of individuals carrying both rare polymorphic alleles was significantly higher compared to healthy women. CONCLUSIONS.: Our findings support the hypothesis that low penetrant polymorphisms of progesterone receptor may modify the risk for ovarian cancer. Our data do not allow drawing a clear conclusion on the risk for breast cancer

HERG mutation predicts short QT based on channel kinetics but causes long QT by heterotetrameric trafficking deficiency

OBJECTIVE: Mutations in the KCNH2 (hERG, human ether-a-go-go related gene) gene may cause a reduction of the delayed rectifier current I(Kr), thereby leading to the long QT syndrome (LQTS). The reduced I(Kr) delays the repolarisation of cardiac cells and renders patients vulnerable to ventricular arrhythmias and sudden death. We identified a novel mutation in a LQTS family and investigated its functional consequences using molecular and microscopic techniques. METHODS AND RESULTS: Genetic screening in the LQTS family revealed a heterozygous frameshift mutation p.Pro872fs located in the C-terminus of the KCNH2 gene. The mutation leads to a premature truncation of the C-terminus of the hERG protein. p.Pro872fs channels lack 282 amino acids at the C-terminus and possess an extra 4-amino acid tail. Both the kinetic and biochemical properties of the p.Pro872fs and p.Pro872fs/WT channels were studied in HEK293 cells and resulted in a novel proof of concept for heterozygous LQTS mutations: homotetrameric p.Pro872fs channels displayed near-normal expression, trafficking, and channel kinetics. Unexpectedly, upon co-expression of p.Pro872fs and WT channels, the repolarising power (the proportion of hERG current contributing to the action potential as the percentage of the total current available) was substantially higher during action potential clamp experiments as compared to WT channels alone. This would lead to a shorter rather than a prolonged QT interval. However, at the same time, heterotetramerisation of p.Pro872fs and WT channels also caused a dominant negative effect on trafficking by an increase in ER retention of these heterotetrameric channels, which surpassed the former gain in repolarising power. CONCLUSION: The LQTS phenotype in the studied family is caused by a mutation with novel properties. We demonstrate that a KCNH2 mutation that clinically leads to long QT syndrome causes at the cellular level both a "gain" and a "loss" of HERG channel function due to a kinetic increase in repolarising power and a decrease in trafficking efficiency of heteromultimeric channels

Evolution of Dihydropyrimidine Dehydrogenase Diagnostic Testing in a Single Center during an 8-Year Period of Time.

Contains fulltext : 200093.pdf (publisher's version ) (Open Access

Analysis of the human KCNH2(HERG) gene: identification and characterization of a novel mutation Y667X associated with long QT syndrome and a non-pathological 9 bp insertion

Analysis of the human KCNH2(HERG) gene: identification and characterization of a novel mutation Y667X associated with long QT syndrome and a non-pathological 9 bp insertion. Paulussen A, Yang P, Pangalos M, Verhasselt P, Marrannes R, Verfaille C, Vandenberk I, Crabbe R, Konings F, Luyten W, Armstrong M. Department of Pharmacogenomics, Janssen Research Foundation, Janssen Pharmaceutica, Belgium. Long QT (LQT) syndrome is a potentially life-threatening disorder, characterized by a distinct cardiac arrhythmia known as torsades de pointes. Mutations within a number of genes linked to the familial form, including that coding for a cardiac potassium channel called KCNH2 (HERG), have been described based on the characterized genomic organization. A standardized method was developed to screen the entire gene for gene variants. We report a single base pair substitution, introducing a premature STOP codon at codon 667 of the gene in a healthy individual with an extended QTc interval (460 msec). In vitro expression of the codon Y667X variant in Xenopus oocyte suggests that the autosomal dominant variant does not function in a dominant/negative manner and cannot co-assemble to form a channel, resulting in a reduction of the KCNH2 current, and an extension of the QT interval. This indicates that pathogenic LQT gene variants exist in the apparently normal population, the prognosis and clinical consequences of which remain to be determined. The assays described should facilitate future studies into this area. Copyright 2000 Wiley-Liss, Inc