Clinical, genetic and functional analysis of R562S-Kv7.1 mutation associated with long QT syndrome type 1

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Ministry of Education, Youth and Sports of the Czech Republic Introduction Loss-of-function variants of the KCNQ1 gene are associated with life-threatening arrhythmogenic long QT syndrome type 1 (LQT1). This gene encodes structure of the slow delayed rectifier potassium channel (IKs). Some functional characteristics of the C-terminal KCNQ1 variant c.1686G > C (p.R562S) have been recently described [1]. However, accumulation of the current under beta-adrenergic stimulation, essential for shortening the action potential duration during exercise, have not been tested. Purpose The aim of this study was to analyse clinical and genetic characteristics of the R562S variant in our patients and to investigate impact of the variant on IKs channel function with a special focus on reactivity of the channels on beta-adrenergic stimulation. Methods The clinical diagnosis was established according to ESC Guidelines including QTc analysis at rest and after exercise. The molecular genetics diagnostics followed according to current practices (the massive parallel sequencing since 2016). The biophysical analysis was performed on Chinese hamster ovary cells (CHO) by the whole cell patch clamp technique at 37 °C. CHO cells were transiently transfected with wild type (WT) and/or R562S human IKs channels (KCNQ1/KCNE1/Yotiao, 1:2:4). Cyclic adenosine monophosphate (cAMP, 200 µM) and okadaic acid (OA, 0.2 µM) in the pipette solution were used to simulate the beta-adrenergic stimulation. In the confocal microscopy experiments, expression of Yotiao was omitted and GFP-tagged KCNQ1 was used. Results The variant R562S-Kv7.1 has been identified in 7 heterozygous carriers from 3 putatively unrelated families in the Czech Republic. The genotype was associated with long QT syndrome phenotype (prolonged QTc, symptoms including syncopes and aborted cardiac arrest) in some of the carriers. The basic functional analysis proved that both homozygous and heterozygous R562S channels are expressed on the cell membrane (confocal microscopy) and carry IKs (whole cell patch clamp) which agrees with the recently published data on this variant. Importantly, reactivity on beta-adrenergic stimulation was absent in both homozygous and heterozygous R562S channels (n = 14 and 8, respectively), but present in the wild-type channels (increase by 51.4 ± 11.1 % at 120-s cAMP/OA diffusion; n = 12). Conclusions The R562S-Kv7.1 variant may be a founder LQT1 variant in our region which will be further investigated in the future. This variant impairs response of IKs channel to beta-adrenergic stimulation. Absence of this essential regulation may considerably aggravate the channel dysfunction and, thus, may result in life-threatening arrhythmias in R562S carriers during exercise.