Inherited Arrhythmogenic Diseases

Twelve years after the identification of the molecular bases of the long-QT syndrome, it is now possible to express some considerations on the impact that genetic findings have had in the understanding of inherited arrhythmogenic diseases. Along with the excitement for the emerging data on genotype/phenotype correlation and for the development of the first recommendations for gene-specific management of patients, it is also important to acknowledge the unexpected complexity that has emerged. The focus of this article is to analyze the elusive aspects of the relationship between genetic defects and clinical manifestations and to propose some research directions that may provide the needed answers to move forward in the understanding of the genetics of heart rhythm abnormalities

Brugada syndrome

A novel clinical entity characterized by ST segment elevation in right precordial leads (V1 to V3), incomplete or complete right bundle branch block, and susceptibility to ventricular tachyarrhythmia and sudden cardiac death has been described by Brugada et al. in 1992. This disease is now frequently called "Brugada syndrome" (BrS). The prevalence of BrS in the general population is unknown. The suggested prevalence ranges from 5/1,000 (Caucasians) to 14/1,000 (Japanese). Syncope, typically occurring at rest or during sleep (in individuals in their third or fourth decades of life) is a common presentation of BrS. In some cases, tachycardia does not terminate spontaneously and it may degenerate into ventricular fibrillation and lead to sudden death. Both sporadic and familial cases have been reported and pedigree analysis suggests an autosomal dominant pattern of inheritance. In approximately 20% of the cases BrS is caused by mutations in the SCN5A gene on chromosome 3p21-23, encoding the cardiac sodium channel, a protein involved in the control of myocardial excitability. Since the use of the implantable cardioverter defibrillator (ICD) is the only therapeutic option of proven efficacy for primary and secondary prophylaxis of cardiac arrest, the identification of high-risk subjects is one of the major goals in the clinical decision-making process. Quinidine may be regarded as an adjunctive therapy for patients at higher risk and may reduce the number of cases of ICD shock in patients with multiple recurrences

The long QT syndrome

Major progress has taken place, and at a very rapid pace, in the understanding of the congenital long QT syndrome (LQTS). This has been the direct consequence of the identification of several of the genes responsible for LQTS and of the studies that have followed, at both basic and clinical levels. A key issue is represented by the fact that all LQTS genes identified so far encode for ionic channels involved in the control of repolarization. The expression studies of the mutated genes have allowed identification of the specific electrophysiologic consequences of the specific mutations and have demonstrated alterations in the NA+ and in K+ currents sufficient to explain the prolongation of action potential duration and, hence, of the QT interval. Ongoing studies in the selected LQTS patients, for whom the specific mutations are known, are allowing a unique understanding of the complex genotype-phenotype correlation. These studies indicate the existence of what appear to be gene-specific patterns in many clinically important features such as the response to therapeutic interventions, the response to increases in heart rate, and in the factors that precipitate the life-threatening arrhythmias typical of this intriguing disease

The Structural–Functional Crosstalk of the Calsequestrin System: Insights and Pathological Implications

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Arrhythmogenic Mechanism of Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a highly lethal form of inherited arrhythmogenic disease characterized by adrenergically mediated polymorphic VT. The identification of the genetic substrate of the disease has allowed to achieve important milestones in the understanding of the arrhythmogenic mechanisms of the disease. Abnormal calcium leak from the mutant cardiac ryanodine receptor has been associated with the induction of delayed afterdepolarization suggesting that arrhythmogenesis in CPVT is likely to be induced by triggered activity. Here we review the current knowledge and some controversial issues about the molecular mechanism of arrhythmias initiation in CPVT and we discuss their implications for the development of novel therapeutic strategies in CPVT

Genome Editing and Inherited Cardiac Arrhythmias.

Inherited arrhythmic disorders are a group of heterogeneous diseases predisposing to life-threatening arrhythmias and sudden cardiac death. Their diagnosis is not always simple due to incomplete penetrance and genetic heterogeneity. Furthermore, the available treatments are usually invasive and merely preventive. Genome editing and especially CRISPR/Cas9 technologies have the potential to correct the genetic arrhythmogenic substrate, thereby offering a cure for these fatal diseases. To date, genome editing has allowed reproducing cardiac arrhythmias in vitro, providing a robust platform for variant pathogenicity, mechanistic, and drug-testing studies. However, in vivo approaches still need profound research regarding safety, specificity, and efficiency of the methods.S

Gating Properties of <i>SCN5A</i> Mutations and the Response to Mexiletine in Long-QT Syndrome Type 3 Patients

Background— Mexiletine (Mex) has been proposed as a gene-specific therapy for patients with long-QT syndrome type 3 (LQT3) caused by mutations in the cardiac sodium channel gene ( SCN5A ). The degree of QT shortening and the protection from arrhythmias vary among patients harboring different mutations. We tested whether the clinical response to Mex in LQT3 could be predicted by the biophysical properties of the different mutations. Methods and Results— We identified 4 SCN5A mutations in 5 symptomatic LQT3 patients with different responses to Mex (6 to 8 mg · kg −1 · d −1 ). We classified the mutations as sensitive to Mex (P1332L, R1626P; ≥10% of QTc shortening and QTc <500 ms or no arrhythmias) or insensitive to Mex (S941N, M1652R; negligible or no QTc shortening and sudden death). We measured Na + current from HEK 293 cells transfected with wild-type (WT) or mutant Nav1.5. All mutations showed impaired inactivation of Na + current, but the mutations identified in patient responders to Mex (P1332L, R1626P) showed a hyperpolarizing shift of V 1/2 of steady-state inactivation. Furthermore, Mex produced use-dependent block with the order R1626P=P1332L>S941N=WT>M1652R, suggesting that Mex-sensitive mutants present prolonged recovery from Mex block. Conclusions— We propose that voltage dependence of channel availability and shifts of V 1/2 of steady-state inactivation correlate with the clinical response observed in LQT3 patients. This supports the view that the response to Mex is mutation specific and that in vitro testing may help to predict the response to therapy in LQT3

Role of the JP45-Calsequestrin Complex on Calcium Entry in Slow Twitch Skeletal Muscles

We exploited a variety of mouse models to assess the roles of JP45-CASQ1 (CASQ, calsequestrin) and JP45-CASQ2 on calcium entry in slow twitch muscles. In flexor digitorum brevis (FDB) fibers isolated from JP45-CASQ1-CASQ2 triple KO mice, calcium transients induced by tetanic stimulation rely on calcium entry via La3+- and nifedipine-sensitive calcium channels. The comparison of excitation-coupled calcium entry (ECCE) between FDB fibers from WT, JP45KO, CASQ1KO, CASQ2KO, JP45-CASQ1 double KO, JP45-CASQ2 double KO, and JP45-CASQ1-CASQ2 triple KO shows that ECCE enhancement requires ablation of both CASQs and JP45. Calcium entry activated by ablation of both JP45-CASQ1 and JP45-CASQ2 complexes supports tetanic force development in slow twitch soleus muscles. In addition, we show that CASQs interact with JP45 at Ca2+ concentrations similar to those present in the lumen of the sarcoplasmic reticulum at rest, whereas Ca2+ concentrations similar to those present in the SR lumen after depolarization-induced calcium release cause the dissociation of JP45 from CASQs. Our results show that the complex JP45-CASQs is a negative regulator of ECCE and that tetanic force development in slow twitch muscles is supported by the dynamic interaction between JP45 and CASQs

An ICT infrastructure to integrate clinical and molecular data in oncology research

<p>Abstract</p> <p>Background</p> <p>The ONCO-i2b2 platform is a bioinformatics tool designed to integrate clinical and research data and support translational research in oncology. It is implemented by the University of Pavia and the IRCCS Fondazione Maugeri hospital (FSM), and grounded on the software developed by the Informatics for Integrating Biology and the Bedside (i2b2) research center. I2b2 has delivered an open source suite based on a data warehouse, which is efficiently interrogated to find sets of interesting patients through a query tool interface.</p> <p>Methods</p> <p>Onco-i2b2 integrates data coming from multiple sources and allows the users to jointly query them. I2b2 data are then stored in a data warehouse, where facts are hierarchically structured as ontologies. Onco-i2b2 gathers data from the FSM pathology unit (PU) database and from the hospital biobank and merges them with the clinical information from the hospital information system.</p> <p>Our main effort was to provide a robust integrated research environment, giving a particular emphasis to the integration process and facing different challenges, consecutively listed: biospecimen samples privacy and anonymization; synchronization of the biobank database with the i2b2 data warehouse through a series of Extract, Transform, Load (ETL) operations; development and integration of a Natural Language Processing (NLP) module, to retrieve coded information, such as SNOMED terms and malignant tumors (TNM) classifications, and clinical tests results from unstructured medical records. Furthermore, we have developed an internal SNOMED ontology rested on the NCBO BioPortal web services.</p> <p>Results</p> <p>Onco-i2b2 manages data of more than 6,500 patients with breast cancer diagnosis collected between 2001 and 2011 (over 390 of them have at least one biological sample in the cancer biobank), more than 47,000 visits and 96,000 observations over 960 medical concepts.</p> <p>Conclusions</p> <p>Onco-i2b2 is a concrete example of how integrated Information and Communication Technology architecture can be implemented to support translational research. The next steps of our project will involve the extension of its capabilities by implementing new plug-in devoted to bioinformatics data analysis as well as a temporal query module.</p