In silico screening of the impact of hERG channel kinetic abnormalities on channel block and susceptibility to acquired long QT syndrome

Accurate diagnosis of predisposition to long QT syndrome is crucial for reducing the risk of cardiac arrhythmias. In recent years, drug-induced provocative tests have proved useful to unmask some latent mutations linked to cardiac arrhythmias. In this study we expanded this concept by developing a prototype for a computational provocative screening test to reveal genetic predisposition to acquired long-QT syndrome (aLQTS). We developed a computational approach to reveal the pharmacological properties of I blocking drugs that are most likely to cause aLQTS in the setting of subtle alterations in I channel gating that would be expected to result from benign genetic variants. We used the model to predict the most potentially lethal combinations of kinetic anomalies and drug properties. In doing so, we also implicitly predicted ideal inverse therapeutic properties of K channel openers that would be expected to remedy a specific defect We systematically performed "in silico mutagenesis" by altering discrete kinetic transition rates of the Fink et al. Markov model of human l channels, corresponding to activation, inactivation, deactivation and recovery from inactivation of I-Kr channels. We then screened and identified the properties of IKr blockers that caused acquired long QT and therefore unmasked mutant phenotypes for mild, moderate and severe variants. Mutant I-Kr channels were incorporated into the O'Hara et al. human ventricular action potential (AP) model and subjected to simulated application of a wide variety of I-drug interactions in order to identify the characteristics that selectively exacerbate the AP duration (APD) differences between wild-type and IKr mutated cells. Our results show that drugs with disparate affinities to conformation states of the I-Kr, channel are key to amplify variants underlying susceptibility to acquired long QT syndrome, an effect that is especially pronounced at slow frequencies. Finally, we developed a mathematical formulation of the M54T MiRP1 latent mutation and simulated a provocative test. In this setting, application of dofetilide dramatically amplified the predicted QT interval duration in the M54T hMiRP1 mutation compared to wild-type.This work was partially supported by the "VI Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica" from the Ministerio de Economia y Competitividad of Spain (TIN2012-37546-CO3-01) and the European Commission (European Regional Development Funds - ERDF-FEDER), Programa de Apoyo a la Investigacion y Desarrollo de la Universidad Politecnica de Valencia (PAID-00-10-3212) to L.R., Direccion General de Politica Cientifica de la Generalitat Valenciana (GV/2013/119), and Programa Prometeo de la Conselleria d'Educacio Formacio I Ocupacio, Generalitat Valenciana (PROMETEO/ 2012/030). The research was also supported by the American Heart Association (GIAs (10GRNT3880050, 13GRNT14370019), Western States Affiliate), Alfred P. Sloan Foundation, the National Institutes of Health NHLBI R01-HL-085592 and a research grant from Gilead Sciences (to CEC).Romero Pérez, L.; Trénor Gomis, BA.; Yang, P.; Saiz Rodríguez, FJ.; Clancy, CE. (2014). In silico screening of the impact of hERG channel kinetic abnormalities on channel block and susceptibility to acquired long QT syndrome. Journal of Molecular and Cellular Cardiology. 72:126-137. https://doi.org/10.1016/j.yjmcc.2014.02.018S1261377

Dynamic location problems with limited look-ahead

Background Among the most frequently encountered mutations in dilated cardiomyopathy (DCM) are those in the lamin A/C (LMNA) gene. Our goal was to analyze the LMNA gene in patients with DCM and/or conduction disease referred to the cardiogenetics outpatient clinic and to evaluate the prevalence of LMNA mutations and their clinical expression. Methods and Results The LMNA gene was screened in 61 index patients. Eleven mutations (including 6 novel) were identified, mainly in the subgroup of familial DCM with cardiac conduction disease (3/10 index patients) and in patients with DCM and Emery-Dreifuss, Limb-Girdle, or unclassified forms of muscular dystrophy (7/8 index patients). In addition, a mutation was identified in 1 of 4 families with only cardiac conduction disease. We did not identify any large deletions or duplications.Genotype-phenotype relationships revealed a high rate of sudden death and cardiac transplants in carriers of the p.N 195K mutation. Our study confirmed that the p.R225X mutation leads to cardiac conduction disease with late or no development of DCM, underscoring the importance of this mutation in putative familial "lone conduction disease." Nearly one third of LMNA mutation carriers had experienced a thromboembolic event. Conclusions This study highlights the role of LMNA mutations in DCM and related disorders. A severe phenotype in p.N 195K mutation carriers and preferential cardiac conduction disease in p.R225X carriers was encountered. Because of the clinical variability, including the development of associated symptoms in time, LMNA screening should be considered in patients with DCM or familial lone conduction diseas

Changes in Channel Trafficking and Protein Stability Caused by LQT2 Mutations in the PAS Domain of the HERG Channel

Inherited human long-QT2 syndrome (LQTS) results from mutations in the gene encoding the HERG channel. Several LQT2-associated mutations have been mapped to the amino terminal cytoplasmic Per-Arnt-Sim (PAS) domain of the HERG1a channel subunit. Here we have characterized the trafficking properties of some LQT2-associated PAS domain mutants and analyzed rescue of the trafficking mutants by low temperature (27°C) or by the pore blocker drug E4031. We show that the LQT2-associated mutations in the PAS domain of the HERG channel display molecular properties that are distinct from the properties of LQT2-associated mutations in the trans-membrane region. Unlike the latter, many of the tested PAS domain LQT2-associated mutations do not result in trafficking deficiency of the channel. Moreover, the majority of the PAS domain mutations that cause trafficking deficiencies are not rescued by a pore blocking drug. We have also explored the in vitro folding stability properties of isolated mutant PAS domain proteins using a thermal unfolding fluorescence assay and a chemical unfolding assay

Clinical diagnosis of Long QT Syndrome: back to the caliper.

In the last 10 years, the management of cardiac arrhythmias has evolved to an impressive pace, thanks to the development of highly sophisticated technologies for diagnosis and treatment. Mapping of the site of origin of arrhythmias, ablation, and implant of defibrillators have reduced the importance of the traditional approaches based on electrocardiographic reading and prescription of drugs. In this context, inherited arrhythmogenic diseases such as long QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia, short QT syndrome, and Brugada syndrome represent the exception in which the ECG has remained the pivotal diagnostic tool. When approaching the diagnosis of one of these diseases, the cardiologist has to leave fancy computer screens and go back to the ‘ruler and caliper’ to measure the duration of an ‘interval’ or the elevation of an electrocardiographic ‘segment’. This apparently simple diagnosis, however, is far from being easy and even ‘experts’ in the field may face substantial diagnostic dilemma

New insights into the long-QT syndrome

The long QT syndrome (LQTS) is an arrhythmogenic disease in which the prolongation of cardiac repolarization alters the heart's electrical stability and predisposes affected individuals to cardiac arrest. The first arrhythmic events occur during adolescence, and are largely triggered by increased sympathetic activity. Mutations in genes encoding ion channels or proteins that control these channels have emerged as the basis of LQTS. The molecular investigation of LQTS flourished from the mid-nineties. At present, 70% of the population can be genotyped LQTS. Researchers are looking for other causative genes, and have even ventured into non-coding regions of LQTS genes in an attempt to genotype the remaining 30% of patients with LQTS. It has also developed strategies to integrate genotyping in clinical practice. In the clinical setting, the tremendous effort invested in major international registrations of LQTS is already bearing fruit. These studies provide new data on the natural history of LQTS and the response to treatment of patients with genotyped LQTS. This editorial and the accompanying review article published in this edition of Spanish Journal of Cardiology highlights recent advances relevant to the clinical management of affected patients

The Brugada syndrome

PURPOSE OF REVIEW: The Brugada syndrome has been an area of intensive investigation since its earliest description in 1992, both on a clinical and on a basic research level. In this review, we will focus on recent achievements in the molecular dissection of the disease pathophysiology and on large multicenter studies dealing with prognostic markers and the natural history of the Brugada syndrome. RECENT FINDINGS: In the past year, two additional genetic pathways have been associated with the disease. Also, an inflammatory or infectious etiology has recently been linked with the Brugada syndrome. The debate on the predictive role of programmed electrical stimulation is still ongoing. Very recently, large follow-up studies questioned the prognostic role of programmed electrical stimulation in this disease. SUMMARY: Knowledge on the genetic determinants of the Brugada syndrome remains limited. Therefore, the management and the risk stratification of patients should be performed on a clinical basis. Sufficient evidence exists to reassure clinicians who feel reluctant to include programmed electrical stimulation in the risk stratification strategy of asymptomatic Brugada syndrome patients