A Novel KCNH2 S981fs Mutation Identified by Whole-Exome Sequencing Is Associated with Type 2 Long QT Syndrome

Figures

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  Figure 1. (A) (Upper half) Sequencing result (reverse sequence chromatogram) showing the KCNH2 c.2941-2948 AGCGACAC 8 bp deletion mutation (S981Lfs*135). (Lower half) Schematic of the hERG protein important domains and the location of frameshift mutation S981Lfs*135. (B) Electrocardiogram (ECG) strip recording of the proband during her emergency room visit, displaying torsades de pointes and ventricular tachycardia before and after cardioversion. (C) Twelve-lead ECG of the proband after cardioversion, demonstrating a prolonged QT interval.

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  Figure 2. (Upper half) The current densities of HEK293T cells transfected with wild type (WT) and S981fs (8del). (Lower half) Quantification of step currents and tail currents for WT and S981fs hERG channels. The tail currents were normalized with Boltzmann equation to fit with the average data. *, p < 0.05.

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  Figure 3. (A) Western blot analysis comparing wild-type (WT) and S981Lfs hERG proteins. The upper band (155 kDa) represents mature hERG, while the lower band (135 kDa) corresponds to immature hERG. Alpha tubulin (Tub) serves as a control. (B) HEK293T cells transfected with S981Lfs were incubated under different conditions, including low temperature (27 °C), E4031, Vehicle (V), Cisapride (C), or Nicorandil (N), resulting in increased expression of both mature and immature hERG channels. (C) Current–voltage relationship of HEK293T cells transfected with WT and S981Lfs (8del), incubated with or without E4031; * p < 0.05, # p < 0.05. (D) Co-transfection of WT-HERG-GFP and untagged WT- or S981Lfs-HERG constructs in HEK293T cells. Immunoprecipitation (IP) with anti-GFP antibody followed by Western blotting (IB) using anti-hERG antibody revealed the presence of both WT and S981Lfs proteins. (E) Confocal imaging of non-permeabilized HEK293T cells transfected with either WT or S981fs proteins (without GFP tag), incubated with anti-hERG antibody against extracellular peptide. The images demonstrate detectable expression of WT and S981fs hERG on the cell membranes, with weaker fluorescence observed…

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  Figure 4. (A) Western blot of HEK293T cells mono-transfected with S981fs (upper half) and co-transfected with wild-type (WT) and S981fs hERG (WT/S981fs) (lower half) pre-treated with or without G418 (using DMSO as a vehicle). The upper band (155 kDa) was recognized as mature hERG, and the lower band (135 kDa) was shown as immature hERG. Alpha tubulin (Tub) was detected as control. The relative expression level of hERG protein was quantified by densitometry and normalized to the control level, which was set at 1.0. Each value represents mean ± SE of more than three independent experiments. (B) HERG current traces and current-voltage relationship of cells co-transfected with WT and S981fs hERG (WT*8DEL) incubated with or without G418; * p < 0.05, # p < 0.05.