A de novo gain-of-function KCND3 mutation in early repolarization syndrome.

<bold>Background: </bold>Early repolarization syndrome (ERS) is characterized by J-point elevation on electrocardiograms and ventricular fibrillation (VF). Early repolarization arises from augmentation of the transmural electrical gradient in the cardiac action potential; therefore, the transient outward potassium current (Ito) has been regarded as a key candidate current for elucidating the mechanism of ERS. KCND3 encoding Kv4.3, an α-subunit of the Ito channel, is considered as one of target genes.<bold>Objective: </bold>The purpose of this study was to search for novel KCND3 mutations associated with ERS and to clarify the pathogenesis.<bold>Methods: </bold>We performed genetic screening for 11 unrelated probands with ERS and analyzed the electrophysiological properties of detected mutations by patch-clamp methods.<bold>Results: </bold>A novel de novo KCND3 heterozygous mutation, Gly306Ala (c.917g>c), was found in 1 proband. The proband was a 12-year-old boy, who suffered VF storm and showed significant J-point elevation in multiple leads. Intravenous isoproterenol and subsequent administration of quinidine were effective in preventing VF recurrence and restored the J-point elevation. In electrophysiological analysis, cultured cells expressing mutant Kv4.3 showed significantly increased current densities, slow inactivation, and slow recovery from inactivation compared to wild type. Extracellular application of quinidine significantly restored the inactivation time course in mutant Kv4.3. A simulation study confirmed the relationship between the novel KCND3 mutation and early repolarization on electrocardiograms.<bold>Conclusion: </bold>A novel KCND3 heterozygous mutation was found to be associated with ERS. The pathogenesis can be explained by the increased Ito. Genetic screening for KCND3 could be useful for understanding the pathogenesis and selecting effective treatment. [ABSTRACT FROM AUTHOR]