Enhanced Effects of Isoflurane on the Long QT Syndrome 1–associated A341V Mutant

Abstract Background: The impact of volatile anesthetics on patients with inherited long QT syndrome (LQTS) is not well understood. This is further complicated by the different genotypes underlying LQTS. No studies have reported on the direct effects of volatile anesthetics on specific LQTS-associated mutations. We investigated the effects of isoflurane on a common LQTS type 1 mutation, A341V, with an unusually severe phenotype. Methods: Whole cell potassium currents (IKs) were recorded from HEK293 and HL-1 cells transiently expressing/coexpressing wild-type KCNQ1 (α-subunit), mutant KCNQ1, wild-type KCNE1 (β-subunit), and fusion KCNQ1 + KCNE1. Current was monitored in the absence and presence of clinically relevant concentration of isoflurane (0.54 ± 0.05 mM, 1.14 vol %). Computer simulations determined the resulting impact on the cardiac action potential. Results: Isoflurane had significantly greater inhibitory effect on A341V + KCNE1 (62.2 ± 3.4%, n = 8) than on wild-type KCNQ1 + KCNE1 (40.7 ± 4.5%; n = 9) in transfected HEK293 cells. Under heterozygous conditions, isoflurane inhibited A341V + KCNQ1 + KCNE1 by 65.2 ± 3.0% (n = 13) and wild-type KCNQ1 + KCNE1 (2:1 ratio) by 32.0 ± 4.5% (n = 11). A341V exerted a dominant negative effect on IKs. Similar differential effects of isoflurane were also observed in experiments using the cardiac HL-1 cells. Mutations of the neighboring F340 residue significantly attenuated the effects of isoflurane, and fusion proteins revealed the modulatory effect of KCNE1. Action potential simulations revealed a stimulation frequency–dependent effect of A341V. Conclusions: The LQTS-associated A341V mutation rendered the IKs channel more sensitive to the inhibitory effects of isoflurane compared to wild-type IKs in transfected cell lines; F340 is a key residue for anesthetic action.

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Suppression-Replacement KCNQ1 Gene Therapy for Type 1 Long QT Syndrome

Circulation ◽

10.1161/circulationaha.120.051836 ◽

2021 ◽

Author(s):

Steven M. Dotzler ◽

C.S. John Kim ◽

William A.C. Gendron ◽

Wei Zhou ◽

Dan Ye ◽

...

Keyword(s):

Gene Therapy ◽

Long Qt Syndrome ◽

Delayed Rectifier ◽

Loss Of Function ◽

Wild Type ◽

Long Qt ◽

Α Subunit ◽

Cardiac Model ◽

Qt Syndrome

Background: Type 1 long QT syndrome (LQT1) is caused by loss-of-function variants in the KCNQ1 -encoded K v 7.1 potassium channel α-subunit which is essential for cardiac repolarization, providing the slow delayed rectifier current (IKs). No current therapies target the molecular cause of LQT1. Methods: A dual-component "suppression-and-replacement" (SupRep) KCNQ1 gene therapy was created by cloning a KCNQ1 shRNA and a "shRNA-immune" (shIMM) KCNQ1 cDNA modified with silent variants in the shRNA target site, into a single construct. The ability of KCNQ1-SupRep gene therapy to suppress and replace LQT1-causative variants in KCNQ1 was evaluated via heterologous expression in TSA201 cells. For a human in vitro cardiac model, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from four patients with LQT1 (KCNQ1-Y171X, -V254M, -I567S, and -A344A/spl) and an unrelated healthy control. CRISPR-Cas9 corrected isogenic control iPSC-CMs were made for two LQT1 lines (correction of KCNQ1-V254M and KCNQ1-A344A/spl). FluoVolt voltage dye was used to measure the cardiac action potential duration (APD) in iPSC-CMs treated with KCNQ1-SupRep. Results: In TSA201 cells, KCNQ1-SupRep achieved mutation-independent suppression of wild-type KCNQ1 and three LQT1-causative variants (KCNQ1-Y171X, -V254M, and -I567S) with simultaneous replacement of KCNQ1-shIMM as measured by allele-specific qRT-PCR and western blot. Using FluoVolt voltage dye to measure the cardiac APD in the four LQT1 patient-derived iPSC-CMs, treatment with KCNQ1-SupRep resulted in shortening of the pathologically prolonged APD at both 90% (APD 90 ) and 50% (APD 50 ) repolarization resulting in APD values similar to those of the two isogenic controls. Conclusions: This study provides the first proof-of-principle gene therapy for complete correction of LQTS. As a dual-component gene therapy vector, KCNQ1-SupRep successfully suppressed and replaced KCNQ1 to normal wild-type levels. In TSA201 cells, co-transfection of LQT1-causative variants and KCNQ1-SupRep caused mutation-independent suppression-and-replacement of KCNQ1 . In LQT1 iPSC-CMs, KCNQ1-SupRep gene therapy shortened the APD, thereby eliminating the pathognomonic feature of LQT1.

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Abstract 2965: Mutations in SNTA1- Encoded Syntrophin α: Characterization of a Novel Long QT Syndrome Susceptibility Gene Involving the Sodium Channel Macromolecular Complex

Circulation ◽

10.1161/circ.116.suppl_16.ii_662-a ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Argelia Medeiros-Domingo ◽

Carmen Valdivia ◽

Matteo Vatta ◽

Gianrico Farrugia ◽

Jonathan C Makielski ◽

...

Keyword(s):

Sodium Channel ◽

Long Qt Syndrome ◽

Pdz Domain ◽

Susceptibility Gene ◽

Hek293 Cells ◽

Macromolecular Complex ◽

Long Qt ◽

Gain Of Function ◽

Α Subunit ◽

Qt Syndrome

Background: Genes encoding sodium channel interacting proteins (ChIPs) have been identified as novel long QT syndrome (LQTS)-susceptibility genes. Approximately 25% of patients with LQTS remain genotype negative. ChIPs comprising the sodium channel macromolecular complex represent attractive candidates for disease susceptibility. Previously, in human jejunal circular smooth muscle, we demonstrated that syntrophin γ2 regulates sodium channel gating by a PDZ-domain interaction involving the C-terminus. In the heart, syntrophin α is more highly expressed than γ2, therefore, syntrophin α was evaluated as a possible LQTS-susceptibility ChIP. Methods: Comprehensive open reading frame/splice mutational analysis of syntrophin α was performed using PCR, DHPLC, and direct DNA sequencing on a cohort of 50 unrelated patients with LQT1–10 negative/phenotype positive LQTS (34 females; average age at diagnosis 26 ± 16 years; average QTc 531 ± 60.4 ms; QTc range 480 –759 ms). Mutations were engineered by site-directed mutagenesis and transiently expressed in HEK293 cells containing the stably-expressed SCN5A- encoded sodium channel α subunit (hNaV1.5). Results: Analysis of syntrophin α, encoded by SNTA1 , revealed 3 missense mutations in 2 patients (4%). A female diagnosed with LQTS at 13 years (QTc, 480 ms) with family history of autopsy-negative unexplained sudden death, was compound heterozygous for P74L/A257G while a male, diagnosed with LQTS at 18 years following syncopal episodes (QTc, 529 ms), hosted the A390V mutation. These mutations were absent in 600 reference alleles and A257G and A390V involved highly conserved residues. Functional studies revealed a marked leftward shift in sodium current activation for A257G and a significant rightward shift in channel inactivation for A390V-SNTA1. Both kinetic perturbations precipitated a ``gain-of-function” increase in the sodium channel window current. Conclusion: We provide the sentinel report of SNTA1 as a novel LQTS-susceptibility gene with a putative pathogenic mechanism involving a secondary ``gain-of-function” in the NaV1.5 sodium channel. Thus, CAV3-LQTS (LQT9), SCN4B-LQTS (LQT10), and now SNTA1-LQTS represent functional homologues with LQT3-like perturbations.

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Biophysical characteristics of a new mutation on the KCNQ1 potassium channel (L251P) causing long QT syndrome

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y02-162 ◽

2003 ◽

Vol 81 (2) ◽

pp. 129-134 ◽

Cited By ~ 5

Author(s):

Dominic Deschênes ◽

Said Acharfi ◽

Valerie Pouliot ◽

Robert Hegele ◽

Andrew Krahn ◽

...

Keyword(s):

Potassium Channel ◽

Long Qt Syndrome ◽

Potassium Currents ◽

Regulatory Subunit ◽

Dominant Negative Effect ◽

Wild Type ◽

Patch Clamp Technique ◽

Long Qt ◽

New Mutation ◽

Qt Syndrome

The congenital long QT syndrome (LQTS) is a hereditary cardiac disease characterized by prolonged ventricular repolarization, syncope, and sudden death. Mutations causing LQTS have been identified in various genes that encode for ionic channels or their regulatory subunits. Several of these mutations have been reported on the KCNQ1 gene encoding for a potassium channel or its regulatory subunit (KCNE1). In this study, we report the biophysical characteristics of a new mutation (L251P) in the transmembrane segment 5 (S5) of the KCNQ1 potassium channel. Potassium currents were recorded from CHO cells transfected with either wild type or mutant KCNQ1 in the presence or in the absence of its regulatory subunit (KCNE1), using the whole-cell configuration of the patch clamp technique. Wild-type KCNQ1 current amplitudes are increased particularly by KCNE1 co-expression but no current is observed with the KCNQ1 (L251P) mutant either in the presence or in the absence of KCNE1. Coexpressing KCNE1 with equal amount of cDNAs encoding wild type and mutant KCNQ1 results in an 11-fold reduction in the amplitude of potassium currents. The kinetics of activation and inactivation and the activation curve are minimally affected by this mutation. Our results suggest that the dominant negative effect of the P251L mutation on KCNQ1 channel explains the prolonged repolarization in patients carrying this mutation.Key words: long QT syndrome, ventricular fibrillation, potassium channels, KCNQ1.

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Molecular Mechanism of Autosomal Recessive Long QT-Syndrome 1 without Deafness

International Journal of Molecular Sciences ◽

10.3390/ijms22031112 ◽

2021 ◽

Vol 22 (3) ◽

pp. 1112

Author(s):

Annemarie Oertli ◽

Susanne Rinné ◽

Robin Moss ◽

Stefan Kääb ◽

Gunnar Seemann ◽

...

Keyword(s):

Action Potential ◽

Molecular Mechanism ◽

Long Qt Syndrome ◽

Autosomal Recessive ◽

Delayed Rectifier ◽

Loss Of Function ◽

Wild Type ◽

Long Qt ◽

Qt Syndrome ◽

Iks Channel

KCNQ1 encodes the voltage-gated potassium (Kv) channel KCNQ1, also known as KvLQT1 or Kv7.1. Together with its ß-subunit KCNE1, also denoted as minK, this channel generates the slowly activating cardiac delayed rectifier current IKs, which is a key regulator of the heart rate dependent adaptation of the cardiac action potential duration (APD). Loss-of-function mutations in KCNQ1 cause congenital long QT1 (LQT1) syndrome, characterized by a delayed cardiac repolarization and a prolonged QT interval in the surface electrocardiogram. Autosomal dominant loss-of-function mutations in KCNQ1 result in long QT syndrome, called Romano–Ward Syndrome (RWS), while autosomal recessive mutations lead to Jervell and Lange-Nielsen syndrome (JLNS), associated with deafness. Here, we identified a homozygous KCNQ1 mutation, c.1892_1893insC (p.P631fs*20), in a patient with an isolated LQT syndrome (LQTS) without hearing loss. Nevertheless, the inheritance trait is autosomal recessive, with heterozygous family members being asymptomatic. The results of the electrophysiological characterization of the mutant, using voltage-clamp recordings in Xenopus laevis oocytes, are in agreement with an autosomal recessive disorder, since the IKs reduction was only observed in homomeric mutants, but not in heteromeric IKs channel complexes containing wild-type channel subunits. We found that KCNE1 rescues the KCNQ1 loss-of-function in mutant IKs channel complexes when they contain wild-type KCNQ1 subunits, as found in the heterozygous state. Action potential modellings confirmed that the recessive c.1892_1893insC LQT1 mutation only affects the APD of homozygous mutation carriers. Thus, our study provides the molecular mechanism for an atypical autosomal recessive LQT trait that lacks hearing impairment.

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Abstract 5316: hERG 1b as a Potential Target for Inherited and Acquired Long QT Syndrome

Circulation ◽

10.1161/circ.118.suppl_18.s_525-c ◽

2008 ◽

Vol 118 (suppl_18) ◽

Author(s):

Gail A Robertson ◽

Harinath Sale ◽

David Tester ◽

Thomas J O’Hara ◽

Pallavi Phartiyal ◽

...

Keyword(s):

Action Potential ◽

Long Qt Syndrome ◽

Time Course ◽

Drug Sensitivity ◽

Long Qt ◽

Hek 293 ◽

Hek 293 Cells ◽

Acquired Long Qt Syndrome ◽

293 Cells ◽

Qt Syndrome

Cardiac I Kr is a critical repolarizing current in the heart and a target for inherited and acquired long QT syndrome. Biochemical studies show that native I Kr channels are heteromers composed of both hERG 1a and 1b subunits, yet our current understanding of I Kr functional properties derives primarily from studies of homo-oligomers of the original hERG 1a isolate. The hERG 1a and 1b subunits are identical except at the amino (NH2) terminus, which in hERG 1b is much shorter and has a unique primary sequence. We compared the biophysical properties of currents produced by hERG 1a and 1a/1b channels expressed in HEK-293 cells at near-physiological temperatures. We found that heteromeric hERG 1a/1b currents are much larger than hERG 1a currents and conduct 80% more charge during an action potential. This surprising difference corresponds to a two-fold increase in the apparent rates of activation and recovery from inactivation, which reduces rectification and facilitates current rebound during repolarization. Kinetic modeling shows these gating differences account quantitatively for the differences in current amplitude between the two channel types. Depending on the action potential model used, loss of 1b predicts an increase in action potential duration of 27 ms (7%) or 41 ms (17%), respectively. Drug sensitivity was also different. Compared to homomeric 1a channels, heteromeric 1a/1b channels were inhibited by E-4031 with a slower time course and a corresponding four-fold positive shift in the IC 50 . Differences in current kinetics and drug sensitivity were modeled by “NH2 mode” gating with conformational states bound by the amino terminus in hERG 1a homomers but not 1a/1b heteromers. The importance of hERG 1b in vivo is supported by the identification of a 1b-specific A8V missense mutation in 1/269 unrelated genotype-negative LQTS patients and absent in 400 control alleles. Mutant 1bA8V expressed alone or with hERG 1a in HEK-293 cells nearly eliminated 1b protein. Thus, mutations specifically disrupting hERG 1b function are expected to reduce cardiac I Kr , prolong QT interval and enhance drug sensitivity, thus representing a potential mechanism underlying inherited or acquired LQTS.

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Long QT syndrome masquerading as epilepsy

Practical Neurology ◽

10.1136/practneurol-2018-001959 ◽

2018 ◽

Vol 19 (1) ◽

pp. 56-61 ◽

Cited By ~ 1

Author(s):

Clare M Galtrey ◽

Viva Levee ◽

Jan Arevalo ◽

Damian Wren

Keyword(s):

Early Diagnosis ◽

Long Qt Syndrome ◽

Refractory Epilepsy ◽

Near Miss ◽

Long Qt ◽

Her Family ◽

Fatal Arrhythmia ◽

Qt Syndrome ◽

The Impact ◽

Treatable Condition

The diagnosis of epilepsy is incorrect in up to 20% of cases so should be revisited if attacks are not responding to treatment. We present a case of long QT syndrome that remained undiagnosed in the epilepsy clinic for 15 years until a near-fatal arrhythmia revealed the diagnosis and allowed effective treatment of her attacks. We hope this near miss raises awareness of long QT syndrome as a potentially fatal, rare but treatable condition that neurologists must consider in people with a label of refractory epilepsy. We provide practical pointers to increase the chance of early diagnosis and explore the impact of a late diagnosis for the patient and her family.

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