Faculty Bibliography

We describe a mutation (E299V) in KCNJ2, the gene that encodes the strong inward rectifier K(+) channel protein (Kir2.1), in an 11-y-old boy. The unique short QT syndrome type-3 phenotype is associated with an extremely abbreviated QT interval (200 ms) on ECG and paroxysmal atrial fibrillation. Genetic screening identified an A896T substitution in a highly conserved region of KCNJ2 that resulted in a de novo mutation E299V. Whole-cell patch-clamp experiments showed that E299V presents an abnormally large outward IK1 at potentials above -55 mV (P < 0.001 versus wild type) due to a lack of inward rectification. Coexpression of wild-type and mutant channels to mimic the heterozygous condition still resulted in a large outward current. Coimmunoprecipitation and kinetic analysis showed that E299V and wild-type isoforms may heteromerize and that their interaction impairs function. The homomeric assembly of E299V mutant proteins actually results in gain of function. Computer simulations of ventricular excitation and propagation using both the homozygous and heterozygous conditions at three different levels of integration (single cell, 2D, and 3D) accurately reproduced the electrocardiographic phenotype of the proband, including an exceedingly short QT interval with merging of the QRS and the T wave, absence of ST segment, and peaked T waves. Numerical experiments predict that, in addition to the short QT interval, absence of inward rectification in the E299V mutation should result in atrial fibrillation. In addition, as predicted by simulations using a geometrically accurate three-dimensional ventricular model that included the His-Purkinje network, a slight reduction in ventricular excitability via 20% reduction of the sodium current should increase vulnerability to life-threatening ventricular tachyarrhythmia.

The discovery of the genetic basis of inherited arrhythmias has paved the way for an improved understanding of arrhythmogenesis in a wide spectrum of life-threatening conditions. In vitro expression of mutations and transgenic animal models have been instrumental in enhancing this understanding, but the applicability of results to the human heart remains unknown. The ability to differentiate induced pluripotent stem cells (iPSs) into cardiomyocytes enables the potential to generate patient-specific myocytes, which could be used to recapitulate the features of inherited arrhythmias in the context of the patient's genetic background. Few studies have been reported on iPS-derived myocytes obtained from patients with heritable arrhythmias, but they have demonstrated the applicability of this innovative approach to the study of inherited arrhythmias. Here we review the results achieved by iPS investigations in arrhythmogenic syndromes and discuss the existing challenges to be addressed before the use of iPS-derived myocytes can become a part of personalized management of inherited arrhythmias.

In order to support and improve the efficiency of clinical research in specific health area, the University of Pavia and the IRCCS Fondazione Salvatore Maugeri of Pavia (FSM) are developing and implementing an i2b2 based platform, designed to collect data coming from hospital clinical practice and scientific research. The work made in FSM is committed to support an affordable, less intrusive and more personalized care, increasing the quality of clinical practice as well as improving the scientific results. Such a aim depends on the application of information and communication technologies and the use of data. An integrated data warehouse has been implemented to support clinicians and researchers in two medical fields with a great impact on the population: oncology and cardiology. Furthermore the data warehouse approach has been tested with administrative information, allowing a financial view of clinical data.

Regulation of calcium flux in the heart is a key process that affects cardiac excitability and contractility. Degenerative diseases, such as coronary artery disease, have long been recognized to alter the physiology of intracellular calcium regulation, leading to contractile dysfunction or arrhythmias. Since the discovery of the first gene mutation associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) in 2001, a new area of interest in this field has emerged--the genetic abnormalities of key components of the calcium regulatory system. Such anomalies cause a variety of genetic diseases characterized by the development of life-threatening arrhythmias in young individuals. In this Review, we provide an overview of the structural organization and the function of calcium-handling proteins and describe the mechanisms by which mutations determine the clinical phenotype. Firstly, we discuss mutations in the genes encoding the ryanodine receptor 2 (RYR2) and calsequestrin 2 (CASQ2). These proteins are pivotal to the regulation of calcium release from the sarcoplasmic reticulum, and mutations can cause CPVT. Secondly, we review defects in genes encoding proteins that form the voltage-dependent L-type calcium channel, which regulates calcium entry into myocytes. Mutations in these genes cause various phenotypes, including Timothy syndrome, Brugada syndrome, and early repolarization syndrome. The identification of mutations associated with 'calcium-handling diseases' has led to an improved understanding of the role of calcium in cardiac physiology.