Flecainide reduces ventricular arrhythmias via a mechanism that differs from that of β-blockers in catecholaminergic polymorphic ventricular tachycardia

AbstractBackgroundCatecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterized by episodic ventricular tachycardia induced by adrenergic stress. Although β-blockers are used as first-line therapy, their therapeutic effects are largely incomplete. Flecainide has recently been shown to modify the molecular defects in CPVT. The aim of this study was to investigate the effects of flecainide as an add-on to conventional therapy on exercise-induced ventricular arrhythmia and compare them with those of conventional therapy alone.MethodsThe study included 5 CPVT patients with a mutation in RYR2. They experienced episodic arrhythmic events despite conventional β-blocker therapy and were therefore given flecainide in addition. The effects of the addition of flecainide therapy on ventricular arrhythmia during exercise testing were compared with those of conventional therapy alone.ResultsBoth β-blockers alone and with additional flecainide increased the maximal workload attained at the onset of ventricular arrhythmia; however, only flecainide increased the sinus rate at the onset of ventricular arrhythmias. Furthermore, flecainide increased the exercise capacity by preventing exercise-induced arrhythmias. During a follow-up period of 17±2 months, 1 patient experienced recurrent arrhythmic episodes that were associated with noncompliance. All patients reported improvements in their ability to perform the activities of daily living.ConclusionFlecainide effectively reduced ventricular arrhythmias via a mechanism that differs from that of β-blockers in genotype-positive patients with CPVT. The specific effects of flecainide may be critical in the improvement noted in the patients' ability to perform daily activities

Ancestral Inference and the Study of Codon Bias Evolution: Implications for Molecular Evolutionary Analyses of the Drosophila melanogaster Subgroup

Reliable inference of ancestral sequences can be critical to identifying both patterns and causes of molecular evolution. Robustness of ancestral inference is often assumed among closely related species, but tests of this assumption have been limited. Here, we examine the performance of inference methods for data simulated under scenarios of codon bias evolution within the Drosophila melanogaster subgroup. Genome sequence data for multiple, closely related species within this subgroup make it an important system for studying molecular evolutionary genetics. The effects of asymmetric and lineage-specific substitution rates (i.e., varying levels of codon usage bias and departures from equilibrium) on the reliability of ancestral codon usage was investigated. Maximum parsimony inference, which has been widely employed in analyses of Drosophila codon bias evolution, was compared to an approach that attempts to account for uncertainty in ancestral inference by weighting ancestral reconstructions by their posterior probabilities. The latter approach employs maximum likelihood estimation of rate and base composition parameters. For equilibrium and most non-equilibrium scenarios that were investigated, the probabilistic method appears to generate reliable ancestral codon bias inferences for molecular evolutionary studies within the D. melanogaster subgroup. These reconstructions are more reliable than parsimony inference, especially when codon usage is strongly skewed. However, inference biases are considerable for both methods under particular departures from stationarity (i.e., when adaptive evolution is prevalent). Reliability of inference can be sensitive to branch lengths, asymmetry in substitution rates, and the locations and nature of lineage-specific processes within a gene tree. Inference reliability, even among closely related species, can be strongly affected by (potentially unknown) patterns of molecular evolution in lineages ancestral to those of interest

Targeting mortalin using conventional and RNA-helicase-coupled hammerhead ribozymes

Mortalin, also known as mot2/mthsp70/GRP75/PBP74, is a member of the heat-shock protein 70 family that is heat-uninducible. It is differentially distributed in cells that have normal and immortal phenotypes, has been localized to various subcellular sites, and has several binding partners and functions. Here, we describe the construction and use of mortalin-specific conventional and hybrid ribozymes to elucidate its crucial role in cell proliferation. Whereas conventional hammerhead ribozymes did not cause any repression of endogenous mortalin expression, RNA-helicase-linked hybrid ribozymes successfully suppressed the expression of mortalin, which resulted in the growth arrest of transformed human cells. We show that, first, RNA helicase-coupled hybrid ribozymes that have a linked unwinding activity can be used to target genes for which conventional hammerhead ribozymes are ineffective; second, the targeting of mortalin by RNA-helicase-coupled hybrid ribozymes causes growth suppression of transformed human cells and could be used as a treatment for cancer