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Allelic Complexity in Long QT Syndrome: A Family-Case Study. Int J Mol Sci 2017; 18:ijms18081633. [PMID: 28749435 PMCID: PMC5578023 DOI: 10.3390/ijms18081633] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 07/13/2017] [Accepted: 07/21/2017] [Indexed: 12/17/2022] Open
Abstract
Congenital long QT syndrome (LQTS) is associated with high genetic and allelic heterogeneity. In some cases, more than one genetic variant is identified in the same (compound heterozygosity) or different (digenic heterozygosity) genes, and subjects with multiple pathogenic mutations may have a more severe disease. Standard-of-care clinical genetic testing for this and other arrhythmia susceptibility syndromes improves the identification of complex genotypes. Therefore, it is important to distinguish between pathogenic mutations and benign rare variants. We identified four genetic variants (KCNQ1-p.R583H, KCNH2-p.C108Y, KCNH2-p.K897T, and KCNE1-p.G38S) in an LQTS family. On the basis of in silico analysis, clinical data from our family, and the evidence from previous studies, we analyzed two mutated channels, KCNQ1-p.R583H and KCNH2-p.C108Y, using the whole-cell patch clamp technique. We found that KCNQ1-p.R583H was not associated with a severe functional impairment, whereas KCNH2-p.C108Y, a novel variant, encoded a non-functional channel that exerts dominant-negative effects on the wild-type. Notably, the common variants KCNH2-p.K897T and KCNE1-p.G38S were previously reported to produce more severe phenotypes when combined with disease-causing alleles. Our results indicate that the novel KCNH2-C108Y variant can be a pathogenic LQTS mutation, whereas KCNQ1-p.R583H, KCNH2-p.K897T, and KCNE1-p.G38S could be LQTS modifiers.
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Yamaguchi Y, Mizumaki K, Hata Y, Sakamoto T, Nakatani Y, Kataoka N, Ichida F, Inoue H, Nishida N. Latent pathogenicity of the G38S polymorphism of KCNE1 K + channel modulator. Heart Vessels 2016; 32:186-192. [PMID: 27255646 DOI: 10.1007/s00380-016-0859-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Accepted: 05/27/2016] [Indexed: 01/08/2023]
Abstract
KCNE1 encodes a modulator of KCNQ1 and KCNH2 channels. Although KCNE1(G38S), a single-nucleotide polymorphism (SNP) causing a G38S substitution in KCNE1, is found frequently, whether and how this SNP causes long QT syndrome (LQTS) remains unclear. We evaluated rate-dependent repolarization dynamics using Holter electrocardiogram (ECG) to assess the pathogenicity of KCNE1(G38S). Forty-five patients exhibiting long QT intervals, as assessed by their baseline ECGs, and 16 control subjects were enrolled. KCNE1(G38S) carriers were identified using genome sequencing. LQTS patients were classified into LQT1 or LQT2 using genetic analysis or epinephrine test. QT-RR relations were determined using 24-h Holter ECG recordings. Among the 15 patients (33.3 %) with KCNE1(G38S), four patients without any mutations or amino acid changes in other major cardiac ion channels were categorized as KCNE1(G38S) carriers. In the QT-RR regression lines, the QT-RR slope was greater in the KCNE1(G38S) carriers and the LQT2 patients (0.215 ± 0.021 and 0.207 ± 0.032, respectively) than in the LQT1 patients (0.163 ± 0.014, P < 0.05) and the control subjects (0.135 ± 0.025, P < 0.001). The calculated QT intervals at an RR interval of 1200 ms were longer in the KCNE1(G38S) carriers and LQT1 and LQT2 patients than in the control subjects. Patients with KCNE1(G38S) had a rate-dependent repolarization abnormality similar to patients with LQT2 and, therefore, may have a potential risk to develop lethal arrhythmias.
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Affiliation(s)
- Yoshiaki Yamaguchi
- Second Department of Internal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Koichi Mizumaki
- Clinical Research and Ethics Center, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan.
| | - Yukiko Hata
- Department of Legal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Tamotsu Sakamoto
- Second Department of Internal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Yosuke Nakatani
- Second Department of Internal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Naoya Kataoka
- Second Department of Internal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Fukiko Ichida
- Department of Pediatrics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Hiroshi Inoue
- Second Department of Internal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
| | - Naoki Nishida
- Department of Legal Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan
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McCauley M, Vallabhajosyula S, Darbar D. Proarrhythmic and Torsadogenic Effects of Potassium Channel Blockers in Patients. Card Electrophysiol Clin 2016; 8:481-93. [PMID: 27261836 DOI: 10.1016/j.ccep.2016.02.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The most common arrhythmia requiring drug treatment is atrial fibrillation (AF), which affects 2 to 5 million Americans and continues to be a major cause of morbidity and increased mortality. Despite recent advances in catheter-based and surgical therapies, antiarrhythmic drugs continue to be the mainstay of therapy for most patients with symptomatic AF. However, many antiarrhythmics block the rapid component of the cardiac delayed rectifier potassium current (IKr) as a major mechanism of action, and marked QT prolongation and pause-dependent polymorphic ventricular tachycardia (torsades de pointes) are major class toxicities.
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Affiliation(s)
- Mark McCauley
- Division of Cardiology, Department of Medicine, University of Illinois at Chicago, 840 South Wood Street, Suite 920 (MC715), Chicago, IL 60612, USA
| | - Sharath Vallabhajosyula
- Division of Cardiology, Department of Medicine, University of Illinois at Chicago, 840 South Wood Street, Suite 920 (MC715), Chicago, IL 60612, USA
| | - Dawood Darbar
- Division of Cardiology, Department of Medicine, University of Illinois at Chicago, 840 South Wood Street, Suite 920 (MC715), Chicago, IL 60612, USA.
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