Sudden cardiac death and channelopathies: a review of implantable defibrillator therapy

Impact of gene patents and licensing practices on access to genetic testing for long QT syndrome

Genetic testing for long QT syndrome exemplifies patenting and exclusive licensing with different outcomes at different times. Exclusive licensing from the University of Utah changed the business model from sole provider to two US providers of long QT syndrome testing. Long QT syndrome is associated with mutations in many genes, 12 of which are now tested by two competing firms in the United States, PGxHealth and GeneDx. Until 2009, PGxHealth was the sole provider, based largely on exclusive rights to patents from the University of Utah and elsewhere. University of Utah patents were initially licensed to DNA Sciences, whose patent rights were acquired by Genaissance, and then by Clinical Data, Inc., which owns PGxHealth. In 2002, DNA Sciences, Inc., "cleared the market" by sending cease-and-desist patent enforcement letters to university and reference laboratories offering long QT syndrome genetic testing. There was no test on the market for a 1- to 2-year period. From 2005-2008, most long QT syndrome-related patents were controlled by Clinical Data, Inc., and its subsidiary PGxHealth. Bio-Reference Laboratories, Inc., secured countervailing exclusive patent rights starting in 2006, also from the University of Utah, and broke the PGxHealth monopoly in early 2009, creating a duopoly for genetic testing in the United States and expanding the number of genes for which commercial testing is available from 5 to 12.

Systems approach to understanding electromechanical activity in the human heart: a national heart, lung, and blood institute workshop summary

The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop of cardiologists, cardiac electrophysiologists, cell biophysicists, and computational modelers on August 20 and 21, 2007, in Washington, DC, to advise the NHLBI on new research directions needed to develop integrative approaches to elucidate human cardiac function. The workshop strove to identify limitations in the use of data from nonhuman animal species for elucidation of human electromechanical function/activity and to identify what specific information on ion channel kinetics, calcium handling, and dynamic changes in the intracellular/extracellular milieu is needed from human cardiac tissues to develop more robust computational models of human cardiac electromechanical activity. This article summarizes the workshop discussions and recommendations on the following topics: (1) limitations of animal models and differences from human electrophysiology, (2) modeling ion channel structure/function in the context of whole-cell electrophysiology, (3) excitation-contraction coupling and regulatory pathways, (4) whole-heart simulations of human electromechanical activity, and (5) what human data are currently needed and how to obtain them. The recommendations can be found on the NHLBI Web site at http://www.nhlbi.nih.gov/meetings/workshops/electro.htm.

Endothelin receptor antagonist CPU0213 and vitamin E reverse downregulation of FKBP12.6 and SERCA2a: a role of hyperphosphorylation of PKCepsilon

Downregulation of FKBP12.6 and sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a) contributes to sudden cardiac death and heart failure. We aimed to test the hypothesis that (i) downregulation of FKBP12.6 and SERCA2a can be taken as molecular markers for drug interventions and (ii) such downregulation is produced by crosstalk between endothelin-reactive oxygen species and beta-adrenoceptors stimulation, mediated by hyperphosphorylation of protein kinase Cvarepsilon (PKCvarepsilon). Rat cardiomyocytes were incubated with isoproterenol (1 microM), endothelin-1 (0.1 microM) or hydrogen peroxide (10 microM) for 18 h, resulting in downregulation of mRNA and protein of FKBP12.6 and SERCA2a, as well as upregulation of PKCvarepsilon mRNA and phosphorylated PKCvarepsilon protein. These changes were reversed by an application of either propranolol (1 microM), endothelin receptor antagonist CPU0213 (1 microM) or vitamin E (1 microM). As indicated by the fluorescent dye Fluo3, diastolic [Ca(2+)](i) in rat ventricular myocytes was increased after incubation with isoproterenol (0.1 microM). The increased [Ca(2+)](i) in diastole was dramatically decreased by CPU0213. Thus, the downregulation of FKBP12.6 and SERCA2a, and hyperphosphorylation of PKCvarepsilon, appear to be related to crosstalk between over-activated endothelin-reactive oxygen species and a beta-adrenoceptor pathway. CPU0213 is beneficial in treating cardiac insufficiency and preventing cardiac arrhythmias possibly by normalizing hyperphosphorylation of PKCvarepsilon and abnormal FKBP12.6 and SERCA2a. The antioxidant activity of vitamin E was sufficient to normalize the levels of FKBP12.6 and SERCA2a and phosphorylation of PKCvarepsilon. Thus by testing with biomarkers FKBP12.6 and SERCA2a, we have shown that the endothelin receptor antagonist CPU0213 and the antioxidant vitamin E may relieve risk of lethal arrhythmias and heart failure by suppressing PKCvarepsilon.

Successful parental use of an automated external defibrillator for an infant with long-QT syndrome

Congenital long-QT syndrome with 2:1 atrioventricular block presenting in the perinatal period is rare, has a poor prognosis, and leads to high risk for lethal ventricular arrhythmic events. An implantable cardioverter-defibrillator seems to be the most effective treatment in the prevention of arrhythmic sudden cardiac death in patients with long-QT syndrome. Technical limitations and risks associated with implantable cardioverter-defibrillators in asymptomatic infants is considered too great to justify use for primary prophylaxis against sudden cardiac death. In this case report we describe the first successful parental use of an automated external defibrillator prescribed for primary prophylaxis against sudden cardiac death in an infant with long-QT syndrome.

Gene Sequencing in Neonates and Infants with the Long QT Syndrome

The objective was to analyze the clinical and molecular findings in a cohort of neonates and infants with the autosomal dominant long QT syndrome (LQTS). Those affected face a high risk of ventricular arrhythmia resulting in syncope, seizure or sudden death. Blood samples submitted for molecular diagnostic studies on 7 infants were subject to DNA extraction and mutation analysis of 18 selected exons in 5 LQTS genes (KCNQ1, HERG, SCN5A, KCNE1, and KCNE2). We detected 11 mutations in these 7 patients. Four patients had 2 mutations in 1 gene (compound heterozygotes) or 2 different genes (digenic inheritance), while 3 patients had 1 mutation each. Except for 1 mutation in KCNE1, all other mutations were detected alone or in combination within HERG and the SCN5A genes. Four of the mutations we found are novel. The lethal nature of the LQTS demands careful attention to the family history and prompt and precise diagnosis and treatment with serious consideration of endocardial pacemaker implantation. While much larger studies are needed, our data suggest that compound heterozygotes or those with 2 mutations in different genes are likely to have a more severe LQTS including early manifestations in neonates and infants.