The Experts below are selected from a list of 1788 Experts worldwide ranked by ideXlab platform
Michael C Sanguinetti - One of the best experts on this subject based on the ideXlab platform.
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Long QT syndrome: ionic basis and arrhythmia mechanism in long QT syndrome type 1.
Journal of cardiovascular electrophysiology, 2000Co-Authors: Michael C SanguinettiAbstract:Long QT syndrome type 1 (LQT1) causes torsades de pointes arrhythmia, ventricular fibrillation, and sudden death. It usually is inherited as an autosomal dominant trait (Romano-Ward syndrome). The primary defect in LQT1 is a mutation in KvLQT1, a gene that encodes the pore-forming alpha-subunit of a K+ channel. KvLQT1 alpha-subunits coassemble with minK beta-subunits to form channels that conduct the slow delayed rectifier K+ current (I(Ks)) in the heart. Recessive mutations in KvLQT1 cause Jervell and Lange-Nielsen syndrome, which is characterized by more severe arrhythmias and congenital neural deafness. Heterologous expression studies demonstrated that mutations in KvLQT1 reduce I(Ks) by causing loss of channel function, altered channel gating, and/or a dominant-negative effect. It remains to be proven that an understanding of the molecular basis of LQT1 will lead to more effective therapy.
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Long QT syndrome-associated mutations in the S4-S5 linker of KvLQT1 potassium channels modify gating and interaction with minK subunits.
The Journal of biological chemistry, 1999Co-Authors: Laura Franqueza, M T Keating, Monica Lin, Igor Splawski, Michael C SanguinettiAbstract:Long QT syndrome is an inherited disorder of cardiac repolarization caused by mutations in cardiac ion channel genes, including KvLQT1. In this study, the functional consequences of three long QT-associated missense mutations in KvLQT1 (R243C, W248R, E261K) were characterized using the Xenopus oocyte heterologous expression system and two-microelectrode voltage clamp techniques. These mutations are located in or near the intracellular linker between the S4 and S5 transmembrane domains, a region implicated in activation gating of potassium channels. The E261K mutation caused loss of function and did not interact with wild-type KvLQT1 subunits. R243C or W248R KvLQT1 subunits formed functional channels, but compared with wild-type KvLQT1 current, the rate of activation was slower, and the voltage dependence of activation and inactivation was shifted to more positive potentials. Co expression of minK and KvLQT1 channel subunits induces a slow delayed rectifier K(+) current, I(Ks), characterized by slow activation and a markedly increased magnitude compared with current induced by KvLQT1 subunits alone. Coexpression of minK with R243C or W248R KvLQT1 subunits suppressed current, suggesting that coassembly of mutant subunits with minK prevented normal channel gating. The decrease in I(Ks) caused by loss of function or altered gating properties explains the prolonged QT interval and increased risk of arrhythmia and sudden death associated with these mutations in KvLQT1.
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functional effects of mutations in KvLQT1 that cause long qt syndrome
Journal of Cardiovascular Electrophysiology, 1999Co-Authors: Z Wang, Martin Tristanifirouzi, Monica Lin, M T Keating, Michael C SanguinettiAbstract:Mutations in KvLQT1. Introduction: The long QT syndrome (LQT) is caused by mutations in genes encoding ion channels that modulate the duration of ventricular action potentials. One of these genes, KvLQT1, encodes an α subunit that coassembles with another subunit, hminK, to form the cardiac slow delayed rectifier (IKs) K+ channel. Methods and Results: The functional effects of seven mutations in KvLQT1 were assessed using two-microelectrode voltage clamp and the Xenopus oocyte expression system. Most mutations in KvLQT1 caused loss of function when expressed alone. Oocytes were also injected with equal amounts of wild-type (WT) KvLQT1 and mutant KvLQT1 cRNA (with or without coinjection of hminK) and the resulting currents compared to currents induced by WT KvLQT1 alone. A341V, RI90Q, or G189R KvLQT1 subunits did not affect expression of WT KvLQT1. The other mutations in KvLQT1 caused a variable degree of dominant-negative suppression of IKs. The order of potency for this effect was G345E > G306R = V254M > A341E. Conclusions: LQTl-associated mutations in KvLQT1 caused a spectrum of dysfunction in IKs and KvLQT1 channels. The degree of IKs dysfunction did not correlate with the QTc interval or the presence of symptoms in the respective gene carriers. In contrast to previous reports, we found that loss of function mutations are not exclusive to recessiveiy inherited LQT.
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Dysfunction of delayed rectifier potassium channels in an inherited cardiac arrhythmia.
Annals of the New York Academy of Sciences, 1999Co-Authors: Michael C SanguinettiAbstract:The rapid (IKr) and slow (IKs) delayed rectifier K+ currents are key regulators of cardiac repolarization. HERG encodes the Kr channel, and KvLQT1 and hminK encode subunits that coassemble to form Ks channels. Mutations in any one of these genes cause Romano-Ward syndrome, an autosomal dominant form of long QT syndrome (LQT). Mutations in KvLQT1 and HERG are the most common cause of LQT. Not all missense mutations of HERG or KvLQT1 have the same effect on K+ channel function. Most mutations result in a dominant-negative effect, but the severity of the resulting phenotype varies widely, as judged by reduction of current induced by coexpression of wild-type and mutant subunits in heterologous expression systems. Mutations in hminK (S74L, D76N) reduce IKs by shifting the voltage dependence of activation and accelerating channel deactivation. A recessive form of LQT is caused by mutations in either KvLQT1 or hminK. The functional consequences of mutations in delayed rectifier K+ channel subunits are delayed cardiac repolarization, lengthened QT interval, and an increased risk of torsade de pointes and sudden death.
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Functional effects of mutations in KvLQT1 that cause long QT syndrome.
Journal of cardiovascular electrophysiology, 1999Co-Authors: Z Wang, Monica Lin, M T Keating, Martin Tristani-firouzi, Michael C SanguinettiAbstract:The long QT syndrome (LQT) is caused by mutations in genes encoding ion channels that modulate the duration of ventricular action potentials. One of these genes, KvLQT1, encodes an alpha subunit that coassembles with another subunit, hminK, to form the cardiac slow delayed rectifier (I(Ks)) K+ channel. The functional effects of seven mutations in KvLQT1 were assessed using two-microelectrode voltage clamp and the Xenopus oocyte expression system. Most mutations in KvLQT1 caused loss of function when expressed alone. Oocytes were also injected with equal amounts of wild-type (WT) KvLQT1 and mutant KvLQT1 cRNA (with or without coinjection of hminK) and the resulting currents compared to currents induced by WT KvLQT1 alone. A341V, R190Q, or G189R KvLQT1 subunits did not affect expression of WT KvLQT1. The other mutations in KvLQT1 caused a variable degree of dominant-negative suppression of I(Ks). The order of potency for this effect was G345E > G306R = V254M > A341E. LQT1-associated mutations in KvLQT1 caused a spectrum of dysfunction in I(Ks) and KvLQT1 channels. The degree of I(Ks) dysfunction did not correlate with the QTc interval or the presence of symptoms in the respective gene carriers. In contrast to previous reports, we found that loss of function mutations are not exclusive to recessively inherited LQT.
Michael Christiansen - One of the best experts on this subject based on the ideXlab platform.
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Clinical characteristics in Long QT syndrome from the Danish Long QT registry
Heart Rhythm, 2005Co-Authors: J. K. Kanters, Egon Toft, Poul E. Bloch Thomsen, Michael ChristiansenAbstract:*p 0.05 KvLQT1 vs. HERG In Denmark patients with mutations in HERG seemed more common than in KvLQT1 and no mutations in SCN5A, MinK, MiRP1 were identified. Compared with the literature they were older at the time at their first symptom, and had generally fewer symptoms. The mortality is low, but cardiac arrest was commonly seen, especially in HERG and patients where the genotype could not be identified.
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t wave morphology analysis distinguishes between KvLQT1 and herg mutations in long qt syndrome
Heart Rhythm, 2004Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Søren Fanoe, Poul Erik Bloch Thomsen, Egon Toft, Michael ChristiansenAbstract:Objectives The aim of this study was to develop an objective method to distinguish between HERG and KvLQT1 genotypes on the surface ECG. Background The two most prevalent genes affected in long QT syndrome (LQTS) are KvLQT1 (KCNQ1) and HERG (KCNH2), which are mutated in >90% of patients with a reported LQTS genotype. It is known that T waves have lower amplitude and more notches in HERG patients than T waves in KvLQT1 patients, but this semiquantitative method lacks the discriminative power to be used in a clinical setting. We developed a simple mathematical method that allowed us to quantify T wave shape in LQTS mutations for clinical use. Methods ECGs from 24 HERG patients, 13 KvLQT1 LQTS patients, and 13 healthy relatives were examined. The repolarizing integral (RI) was constructed from the T wave. The resulting RI is sigmoid and was modeled using the Hill equation as (RI(t) = V max *[ t n /[ K m n + t n ]]). V max is equivalent to the total T wave area, K m is the time when 50% of the T wave area is reached, and n is a measure of the slope of the sigmoid RI. Results The RI correlated nearly perfectly to the fitted sigmoid, r=0.99. In lead V 2 , V max was larger in KvLQT1 (0.148 ± 0.021) (mean ± SE) compared to HERG (0.080 ± 0.012) and controls (0.067 ± 0.021). The Hill coefficient n of the RI discriminated perfectly between HERG (2.00 ± 0.11) and KvLQT1 (4.11 ± 0.15). Conclusions RI allows distinguishing between HERG and KvLQT1 mutations based solely on the T wave morphology in the present LQTS population.
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T wave morphology analysis distinguishes between KvLQT1 and HERG mutations in long QT syndrome.
Heart rhythm, 2004Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Søren Fanoe, Poul Erik Bloch Thomsen, Egon Toft, Michael ChristiansenAbstract:The aim of this study was to develop an objective method to distinguish between HERG and KvLQT1 genotypes on the surface ECG. The two most prevalent genes affected in long QT syndrome (LQTS) are KvLQT1 (KCNQ1) and HERG (KCNH2), which are mutated in >90% of patients with a reported LQTS genotype. It is known that T waves have lower amplitude and more notches in HERG patients than T waves in KvLQT1 patients, but this semiquantitative method lacks the discriminative power to be used in a clinical setting. We developed a simple mathematical method that allowed us to quantify T wave shape in LQTS mutations for clinical use. ECGs from 24 HERG patients, 13 KvLQT1 LQTS patients, and 13 healthy relatives were examined. The repolarizing integral (RI) was constructed from the T wave. The resulting RI is sigmoid and was modeled using the Hill equation as (RI(t) = V(max)*[t(n)/[K(m)(n) + t(n)]]). V(max) is equivalent to the total T wave area, K(m) is the time when 50% of the T wave area is reached, and n is a measure of the slope of the sigmoid RI. The RI correlated nearly perfectly to the fitted sigmoid, r = 0.99. In lead V(2), V(max) was larger in KvLQT1 (0.148 +/- 0.021) (mean +/- SE) compared to HERG (0.080 +/- 0.012) and controls (0.067 +/- 0.021). The Hill coefficient n of the RI discriminated perfectly between HERG (2.00 +/- 0.11) and KvLQT1 (4.11 +/- 0.15). RI allows distinguishing between HERG and KvLQT1 mutations based solely on the T wave morphology in the present LQTS population.
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A single strand conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in 15 exons of the KvLQT1 gene, associated with long QT syndrome
Clinica Chimica Acta, 1999Co-Authors: Lars Allan Larsen, Jorgen K Kanters, Paal Skytt Andersen, Jens Vuust, Joes Ramsøe Jacobsen, Michael ChristiansenAbstract:Congenital long QT syndrome (LQTS) is characterised by prolongation of the QT interval on ECG and cardiac arrhythmias, syncopes and sudden death. A rapid and reliable genetic diagnosis of the disease may be of great importance for diagnosis and treatment of LQTS. Mutations in the KvLQT1 gene, encoding a potassium-channel subunit of importance for the depolarisation of cardiac myocytes, is believed to be associated with 50% of all LQTS cases. Our data confirms that KvLQT1 isoform 1 is encoded by 16 exons, and not 15, as reported previously. We have used genomic DNA sequences to design intronic PCR primers for amplification of 15 exons of KvLQT1 and optimised a non-radioactive single stranded conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in KvLQT1. The sensitivity of the method was 100% when it was tested on 15 in vitro constructed mutants. By multiplexing the PCR amplification of KvLQT1, it is possible to cover all 15 exons in four PCR reactions.
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a single strand conformation polymorphism heteroduplex sscp hd method for detection of mutations in 15 exons of the KvLQT1 gene associated with long qt syndrome
Clinica Chimica Acta, 1999Co-Authors: Lars Allan Larsen, Jorgen K Kanters, Paal Skytt Andersen, Jens Vuust, Joes Ramsøe Jacobsen, Michael ChristiansenAbstract:Congenital long QT syndrome (LQTS) is characterised by prolongation of the QT interval on ECG and cardiac arrhythmias, syncopes and sudden death. A rapid and reliable genetic diagnosis of the disease may be of great importance for diagnosis and treatment of LQTS. Mutations in the KvLQT1 gene, encoding a potassium-channel subunit of importance for the depolarisation of cardiac myocytes, is believed to be associated with 50% of all LQTS cases. Our data confirms that KvLQT1 isoform 1 is encoded by 16 exons, and not 15, as reported previously. We have used genomic DNA sequences to design intronic PCR primers for amplification of 15 exons of KvLQT1 and optimised a non-radioactive single stranded conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in KvLQT1. The sensitivity of the method was 100% when it was tested on 15 in vitro constructed mutants. By multiplexing the PCR amplification of KvLQT1, it is possible to cover all 15 exons in four PCR reactions.
Lars Allan Larsen - One of the best experts on this subject based on the ideXlab platform.
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t wave morphology analysis distinguishes between KvLQT1 and herg mutations in long qt syndrome
Heart Rhythm, 2004Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Søren Fanoe, Poul Erik Bloch Thomsen, Egon Toft, Michael ChristiansenAbstract:Objectives The aim of this study was to develop an objective method to distinguish between HERG and KvLQT1 genotypes on the surface ECG. Background The two most prevalent genes affected in long QT syndrome (LQTS) are KvLQT1 (KCNQ1) and HERG (KCNH2), which are mutated in >90% of patients with a reported LQTS genotype. It is known that T waves have lower amplitude and more notches in HERG patients than T waves in KvLQT1 patients, but this semiquantitative method lacks the discriminative power to be used in a clinical setting. We developed a simple mathematical method that allowed us to quantify T wave shape in LQTS mutations for clinical use. Methods ECGs from 24 HERG patients, 13 KvLQT1 LQTS patients, and 13 healthy relatives were examined. The repolarizing integral (RI) was constructed from the T wave. The resulting RI is sigmoid and was modeled using the Hill equation as (RI(t) = V max *[ t n /[ K m n + t n ]]). V max is equivalent to the total T wave area, K m is the time when 50% of the T wave area is reached, and n is a measure of the slope of the sigmoid RI. Results The RI correlated nearly perfectly to the fitted sigmoid, r=0.99. In lead V 2 , V max was larger in KvLQT1 (0.148 ± 0.021) (mean ± SE) compared to HERG (0.080 ± 0.012) and controls (0.067 ± 0.021). The Hill coefficient n of the RI discriminated perfectly between HERG (2.00 ± 0.11) and KvLQT1 (4.11 ± 0.15). Conclusions RI allows distinguishing between HERG and KvLQT1 mutations based solely on the T wave morphology in the present LQTS population.
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T wave morphology analysis distinguishes between KvLQT1 and HERG mutations in long QT syndrome.
Heart rhythm, 2004Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Søren Fanoe, Poul Erik Bloch Thomsen, Egon Toft, Michael ChristiansenAbstract:The aim of this study was to develop an objective method to distinguish between HERG and KvLQT1 genotypes on the surface ECG. The two most prevalent genes affected in long QT syndrome (LQTS) are KvLQT1 (KCNQ1) and HERG (KCNH2), which are mutated in >90% of patients with a reported LQTS genotype. It is known that T waves have lower amplitude and more notches in HERG patients than T waves in KvLQT1 patients, but this semiquantitative method lacks the discriminative power to be used in a clinical setting. We developed a simple mathematical method that allowed us to quantify T wave shape in LQTS mutations for clinical use. ECGs from 24 HERG patients, 13 KvLQT1 LQTS patients, and 13 healthy relatives were examined. The repolarizing integral (RI) was constructed from the T wave. The resulting RI is sigmoid and was modeled using the Hill equation as (RI(t) = V(max)*[t(n)/[K(m)(n) + t(n)]]). V(max) is equivalent to the total T wave area, K(m) is the time when 50% of the T wave area is reached, and n is a measure of the slope of the sigmoid RI. The RI correlated nearly perfectly to the fitted sigmoid, r = 0.99. In lead V(2), V(max) was larger in KvLQT1 (0.148 +/- 0.021) (mean +/- SE) compared to HERG (0.080 +/- 0.012) and controls (0.067 +/- 0.021). The Hill coefficient n of the RI discriminated perfectly between HERG (2.00 +/- 0.11) and KvLQT1 (4.11 +/- 0.15). RI allows distinguishing between HERG and KvLQT1 mutations based solely on the T wave morphology in the present LQTS population.
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a single strand conformation polymorphism heteroduplex sscp hd method for detection of mutations in 15 exons of the KvLQT1 gene associated with long qt syndrome
Clinica Chimica Acta, 1999Co-Authors: Lars Allan Larsen, Jorgen K Kanters, Paal Skytt Andersen, Jens Vuust, Joes Ramsøe Jacobsen, Michael ChristiansenAbstract:Congenital long QT syndrome (LQTS) is characterised by prolongation of the QT interval on ECG and cardiac arrhythmias, syncopes and sudden death. A rapid and reliable genetic diagnosis of the disease may be of great importance for diagnosis and treatment of LQTS. Mutations in the KvLQT1 gene, encoding a potassium-channel subunit of importance for the depolarisation of cardiac myocytes, is believed to be associated with 50% of all LQTS cases. Our data confirms that KvLQT1 isoform 1 is encoded by 16 exons, and not 15, as reported previously. We have used genomic DNA sequences to design intronic PCR primers for amplification of 15 exons of KvLQT1 and optimised a non-radioactive single stranded conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in KvLQT1. The sensitivity of the method was 100% when it was tested on 15 in vitro constructed mutants. By multiplexing the PCR amplification of KvLQT1, it is possible to cover all 15 exons in four PCR reactions.
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A single strand conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in 15 exons of the KvLQT1 gene, associated with long QT syndrome
Clinica Chimica Acta, 1999Co-Authors: Lars Allan Larsen, Jorgen K Kanters, Paal Skytt Andersen, Jens Vuust, Joes Ramsøe Jacobsen, Michael ChristiansenAbstract:Congenital long QT syndrome (LQTS) is characterised by prolongation of the QT interval on ECG and cardiac arrhythmias, syncopes and sudden death. A rapid and reliable genetic diagnosis of the disease may be of great importance for diagnosis and treatment of LQTS. Mutations in the KvLQT1 gene, encoding a potassium-channel subunit of importance for the depolarisation of cardiac myocytes, is believed to be associated with 50% of all LQTS cases. Our data confirms that KvLQT1 isoform 1 is encoded by 16 exons, and not 15, as reported previously. We have used genomic DNA sequences to design intronic PCR primers for amplification of 15 exons of KvLQT1 and optimised a non-radioactive single stranded conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in KvLQT1. The sensitivity of the method was 100% when it was tested on 15 in vitro constructed mutants. By multiplexing the PCR amplification of KvLQT1, it is possible to cover all 15 exons in four PCR reactions.
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novel donor splice site mutation in the KvLQT1 gene is associated with long qt syndrome
Journal of Cardiovascular Electrophysiology, 1998Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Marianne Orholm, Erik Agner, Paal Skytt Andersen, Jens Vuust, Michael ChristiansenAbstract:KvLQT1 Gene Mutation and LQTS. Introduction: Inherited long QT syndrome (LQTS) recently has been associated with mutations in genes coding for potassium (KVLQTI, KCNEI, and HERG) or sodium (SCN5A) ion channels involved in regulating either sodium inward or potassium outward currents of heart cells, resulting in prolongation of the repolarization period. We describe a new mutation, a-1 donor splice site mutation in a kindred with two affected members (QTc = 0.61 and 0.54 sec). Methods and Results: Single stranded conformation polymorphism (SSCP) analyses were performed on DNA fragments amplified by polymerase chain reaction from DNA extracted from whole blood. Aberrant conformers were analyzed by DNA sequencing. SSCP analysis of the KVLQTI gene revealed an aberrant conformer in the affected family members. DNA sequencing confirmed the presence of a GA change in the last nucleotide of codon 344. This mutation does not cause an amino acid change, but a change of the splice site characteristics at the 3’end of exon 6. The mutation may affect, through deficient splicing, the putative sixth transmembrane segment of the K+ channel, and this type of mutation has not previously been described in KVLQTI. Conclusion: The clinical course of LQTS in the affected family members, in whom no deaths occurred despite 20 to 30 syncopes, can he explained by the ability of the cellular machinery to perform partial correct splicing in the mutant allele. This type of mutation may be misinterpreted as a normal variant, since it is a point mutation causing neither an amino acid change nor the introduction of a stop codon.
Jorgen K Kanters - One of the best experts on this subject based on the ideXlab platform.
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t wave morphology analysis distinguishes between KvLQT1 and herg mutations in long qt syndrome
Heart Rhythm, 2004Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Søren Fanoe, Poul Erik Bloch Thomsen, Egon Toft, Michael ChristiansenAbstract:Objectives The aim of this study was to develop an objective method to distinguish between HERG and KvLQT1 genotypes on the surface ECG. Background The two most prevalent genes affected in long QT syndrome (LQTS) are KvLQT1 (KCNQ1) and HERG (KCNH2), which are mutated in >90% of patients with a reported LQTS genotype. It is known that T waves have lower amplitude and more notches in HERG patients than T waves in KvLQT1 patients, but this semiquantitative method lacks the discriminative power to be used in a clinical setting. We developed a simple mathematical method that allowed us to quantify T wave shape in LQTS mutations for clinical use. Methods ECGs from 24 HERG patients, 13 KvLQT1 LQTS patients, and 13 healthy relatives were examined. The repolarizing integral (RI) was constructed from the T wave. The resulting RI is sigmoid and was modeled using the Hill equation as (RI(t) = V max *[ t n /[ K m n + t n ]]). V max is equivalent to the total T wave area, K m is the time when 50% of the T wave area is reached, and n is a measure of the slope of the sigmoid RI. Results The RI correlated nearly perfectly to the fitted sigmoid, r=0.99. In lead V 2 , V max was larger in KvLQT1 (0.148 ± 0.021) (mean ± SE) compared to HERG (0.080 ± 0.012) and controls (0.067 ± 0.021). The Hill coefficient n of the RI discriminated perfectly between HERG (2.00 ± 0.11) and KvLQT1 (4.11 ± 0.15). Conclusions RI allows distinguishing between HERG and KvLQT1 mutations based solely on the T wave morphology in the present LQTS population.
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T wave morphology analysis distinguishes between KvLQT1 and HERG mutations in long QT syndrome.
Heart rhythm, 2004Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Søren Fanoe, Poul Erik Bloch Thomsen, Egon Toft, Michael ChristiansenAbstract:The aim of this study was to develop an objective method to distinguish between HERG and KvLQT1 genotypes on the surface ECG. The two most prevalent genes affected in long QT syndrome (LQTS) are KvLQT1 (KCNQ1) and HERG (KCNH2), which are mutated in >90% of patients with a reported LQTS genotype. It is known that T waves have lower amplitude and more notches in HERG patients than T waves in KvLQT1 patients, but this semiquantitative method lacks the discriminative power to be used in a clinical setting. We developed a simple mathematical method that allowed us to quantify T wave shape in LQTS mutations for clinical use. ECGs from 24 HERG patients, 13 KvLQT1 LQTS patients, and 13 healthy relatives were examined. The repolarizing integral (RI) was constructed from the T wave. The resulting RI is sigmoid and was modeled using the Hill equation as (RI(t) = V(max)*[t(n)/[K(m)(n) + t(n)]]). V(max) is equivalent to the total T wave area, K(m) is the time when 50% of the T wave area is reached, and n is a measure of the slope of the sigmoid RI. The RI correlated nearly perfectly to the fitted sigmoid, r = 0.99. In lead V(2), V(max) was larger in KvLQT1 (0.148 +/- 0.021) (mean +/- SE) compared to HERG (0.080 +/- 0.012) and controls (0.067 +/- 0.021). The Hill coefficient n of the RI discriminated perfectly between HERG (2.00 +/- 0.11) and KvLQT1 (4.11 +/- 0.15). RI allows distinguishing between HERG and KvLQT1 mutations based solely on the T wave morphology in the present LQTS population.
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a single strand conformation polymorphism heteroduplex sscp hd method for detection of mutations in 15 exons of the KvLQT1 gene associated with long qt syndrome
Clinica Chimica Acta, 1999Co-Authors: Lars Allan Larsen, Jorgen K Kanters, Paal Skytt Andersen, Jens Vuust, Joes Ramsøe Jacobsen, Michael ChristiansenAbstract:Congenital long QT syndrome (LQTS) is characterised by prolongation of the QT interval on ECG and cardiac arrhythmias, syncopes and sudden death. A rapid and reliable genetic diagnosis of the disease may be of great importance for diagnosis and treatment of LQTS. Mutations in the KvLQT1 gene, encoding a potassium-channel subunit of importance for the depolarisation of cardiac myocytes, is believed to be associated with 50% of all LQTS cases. Our data confirms that KvLQT1 isoform 1 is encoded by 16 exons, and not 15, as reported previously. We have used genomic DNA sequences to design intronic PCR primers for amplification of 15 exons of KvLQT1 and optimised a non-radioactive single stranded conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in KvLQT1. The sensitivity of the method was 100% when it was tested on 15 in vitro constructed mutants. By multiplexing the PCR amplification of KvLQT1, it is possible to cover all 15 exons in four PCR reactions.
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A single strand conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in 15 exons of the KvLQT1 gene, associated with long QT syndrome
Clinica Chimica Acta, 1999Co-Authors: Lars Allan Larsen, Jorgen K Kanters, Paal Skytt Andersen, Jens Vuust, Joes Ramsøe Jacobsen, Michael ChristiansenAbstract:Congenital long QT syndrome (LQTS) is characterised by prolongation of the QT interval on ECG and cardiac arrhythmias, syncopes and sudden death. A rapid and reliable genetic diagnosis of the disease may be of great importance for diagnosis and treatment of LQTS. Mutations in the KvLQT1 gene, encoding a potassium-channel subunit of importance for the depolarisation of cardiac myocytes, is believed to be associated with 50% of all LQTS cases. Our data confirms that KvLQT1 isoform 1 is encoded by 16 exons, and not 15, as reported previously. We have used genomic DNA sequences to design intronic PCR primers for amplification of 15 exons of KvLQT1 and optimised a non-radioactive single stranded conformation polymorphism/heteroduplex (SSCP/HD) method for detection of mutations in KvLQT1. The sensitivity of the method was 100% when it was tested on 15 in vitro constructed mutants. By multiplexing the PCR amplification of KvLQT1, it is possible to cover all 15 exons in four PCR reactions.
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novel donor splice site mutation in the KvLQT1 gene is associated with long qt syndrome
Journal of Cardiovascular Electrophysiology, 1998Co-Authors: Jorgen K Kanters, Lars Allan Larsen, Marianne Orholm, Erik Agner, Paal Skytt Andersen, Jens Vuust, Michael ChristiansenAbstract:KvLQT1 Gene Mutation and LQTS. Introduction: Inherited long QT syndrome (LQTS) recently has been associated with mutations in genes coding for potassium (KVLQTI, KCNEI, and HERG) or sodium (SCN5A) ion channels involved in regulating either sodium inward or potassium outward currents of heart cells, resulting in prolongation of the repolarization period. We describe a new mutation, a-1 donor splice site mutation in a kindred with two affected members (QTc = 0.61 and 0.54 sec). Methods and Results: Single stranded conformation polymorphism (SSCP) analyses were performed on DNA fragments amplified by polymerase chain reaction from DNA extracted from whole blood. Aberrant conformers were analyzed by DNA sequencing. SSCP analysis of the KVLQTI gene revealed an aberrant conformer in the affected family members. DNA sequencing confirmed the presence of a GA change in the last nucleotide of codon 344. This mutation does not cause an amino acid change, but a change of the splice site characteristics at the 3’end of exon 6. The mutation may affect, through deficient splicing, the putative sixth transmembrane segment of the K+ channel, and this type of mutation has not previously been described in KVLQTI. Conclusion: The clinical course of LQTS in the affected family members, in whom no deaths occurred despite 20 to 30 syncopes, can he explained by the ability of the cellular machinery to perform partial correct splicing in the mutant allele. This type of mutation may be misinterpreted as a normal variant, since it is a point mutation causing neither an amino acid change nor the introduction of a stop codon.
Pascale Guicheney - One of the best experts on this subject based on the ideXlab platform.
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Mutations in a Dominant-Negative Isoform Correlate with Phenotype in Inherited Cardiac Arrhythmias
American journal of human genetics, 1999Co-Authors: Raha Mohammad-panah, Nathalie Neyroud, Pascale Guicheney, Sophie Demolombe, Isabelle Baró, Florence Kyndt, Maurice J.b. Van Den Hoff, Denis EscandeAbstract:The long QT syndrome is characterized by prolonged cardiac repolarization and a high risk of sudden death. Mutations in the KCNQ1 gene, which encodes the cardiac KvLQT1 potassium ion (K+) channel, cause both the autosomal dominant Romano-Ward (RW) syndrome and the recessive Jervell and Lange-Nielsen (JLN) syndrome. JLN presents with cardiac arrhythmias and congenital deafness, and heterozygous carriers of JLN mutations exhibit a very mild cardiac phenotype. Despite the phenotypic differences between heterozygotes with RW and those with JLN mutations, both classes of variant protein fail to produce K+ currents in cultured cells. We have shown that an N-terminus-truncated KvLQT1 isoform endogenously expressed in the human heart exerts strong dominant-negative effects on the full-length KvLQT1 protein. Because RW and JLN mutations concern both truncated and full-length KvLQT1 isoforms, we investigated whether RW or JLN mutations would have different impacts on the dominant-negative properties of the truncated KvLQT1 splice variant. In a mammalian expression system, we found that JLN, but not RW, mutations suppress the dominant-negative effects of the truncated KvLQT1. Thus, in JLN heterozygous carriers, the full-length KvLQT1 protein encoded by the unaffected allele should not be subject to the negative influence of the mutated truncated isoform, leaving some cardiac K+ current available for repolarization. This is the first report of a genetic disease in which the impact of a mutation on a dominant-negative isoform correlates with the phenotype.
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Heterozygous mutation in the pore of potassium channel gene KvLQT1 causes an apparently normal phenotype in long QT syndrome.
European journal of human genetics : EJHG, 1998Co-Authors: Nathalie Neyroud, Claire Donger, Isabelle Denjoy, Ketty Schwartz, Philippe Coumel, Françoise Gary, Elisabeth Villain, Antoine Leenhardt, Karim Benali, Pascale GuicheneyAbstract:Mutations in KvLQT1, a gene encoding a potassium channel, cause both the recessive Jervell and Lange-Nielsen (JLN) syndrome and the dominant Romano-Ward (RW) syndrome. These diseases are characterised by a prolonged QT interval on the ECG, syncopes and sudden death due to cardiac arrhythmias. The JLN syndrome is also associated with a congenital bilateral deafness. We report here a novel missense mutation, W305S, in the pore region of KvLQT1 identified by PCR-SSCP analysis in two consanguineous JLN families. In contrast to several missense mutations found in the same region of KvLQT1 in RW patients which are associated with severe cardiac phenotypes, the W305S mutation is responsible for an apparently normal phenotype in heterozygous JLN carriers.
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KvLQT1 C-Terminal Missense Mutation Causes a Forme Fruste Long-QT Syndrome
Circulation, 1997Co-Authors: Claire Donger, Isabelle Denjoy, Myriam Berthet, Nathalie Neyroud, Corinne Cruaud, Mohammed Bennaceur, Guy Chivoret, Ketty Schwartz, Philippe Coumel, Pascale GuicheneyAbstract:KvLQT1, the gene encoding the alpha-subunit of a cardiac potassium channel, is the most common cause of the dominant form of long-QT syndrome (LQT1-type), the Romano-Ward syndrome (RWS). The overall phenotype of RWS is characterized by a prolonged QT interval on the ECG and cardiac ventricular arrhythmias leading to recurrent syncopes and sudden death. However, there is considerable variability in the clinical presentation, and potential severity is often difficult to evaluate. To analyze the relationship between phenotypes and underlying defects in KvLQT1, we investigated mutations in this gene in 20 RWS families originating from France.
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KvLQT1 c terminal missense mutation causes a forme fruste long qt syndrome
Circulation, 1997Co-Authors: Claire Donger, Isabelle Denjoy, Myriam Berthet, Nathalie Neyroud, Corinne Cruaud, Mohammed Bennaceur, Guy Chivoret, Ketty Schwartz, Philippe Coumel, Pascale GuicheneyAbstract:Background KvLQT1 , the gene encoding the α-subunit of a cardiac potassium channel, is the most common cause of the dominant form of long-QT syndrome (LQT1-type), the Romano-Ward syndrome (RWS). The overall phenotype of RWS is characterized by a prolonged QT interval on the ECG and cardiac ventricular arrhythmias leading to recurrent syncopes and sudden death. However, there is considerable variability in the clinical presentation, and potential severity is often difficult to evaluate. To analyze the relationship between phenotypes and underlying defects in KvLQT1 , we investigated mutations in this gene in 20 RWS families originating from France. Methods and Results By PCR-SSCP analysis, 16 missense mutations were identified in KvLQT1 , 11 of them being novel. Fifteen mutations, localized in the transmembrane domains S2-S3, S4-S5, P, and S6, were associated with a high percentage of symptomatic carriers (55 of 95, or 58%) and sudden deaths (23 of 95, or 24%). In contrast, a missense mutation, Arg 555 Cys, identified in the C-terminal domain in 3 families, was associated with a significantly less pronounced QT prolongation (459±33 ms, n=41, versus 480±32 ms, n=70, P =.0012), and significantly lower percentages of symptomatic carriers (7 of 44, or 16%, P P Conclusions Our data show a wide KvLQT1 allelic heterogeneity among 20 families in which KvLQT1 causes RWS. We describe the first missense mutation in the C-terminal domain of KvLQT1, which is clearly associated with a fruste phenotype, which could be a favoring factor of acquired LQT syndrome.
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Properties of KvLQT1 K+ channel mutations in Romano–Ward and Jervell and Lange-Nielsen inherited cardiac arrhythmias
The EMBO journal, 1997Co-Authors: Christophe Chouabe, Nathalie Neyroud, Pascale Guicheney, Michel Lazdunski, Georges Romey, Jacques BarhaninAbstract:Mutations in the delayed rectifier K+ channel subunit KvLQT1 have been identified as responsible for both Romano-Ward (RW) and Jervell and Lange-Nielsen (JLN) inherited long QT syndromes. We report the molecular cloning of a human KvLQT1 isoform that is expressed in several human tissues including heart. Expression studies revealed that the association of KvLQT1 with another subunit, IsK, reconstitutes a channel responsible for the IKs current involved in ventricular myocyte repolarization. Six RW and two JLN mutated KvLQT1 subunits were produced and co-expressed with IsK in COS cells. All the mutants, except R555C, fail to produce functional homomeric channels and reduce the K+ current when co-expressed with the wild-type subunit. Thus, in both syndromes, the main effect of the mutations is a dominant-negative suppression of KvLQT1 function. The JLN mutations have a smaller dominant-negative effect, in agreement with the fact that the disease is recessive. The R555C subunit forms a functional channel when expressed with IsK, but with altered gating properties. The voltage dependence of the activation is strongly shifted to more positive values, and deactivation kinetics are accelerated. This finding indicates the functional importance of a small positively charged cytoplasmic region of the KvLQT structure where two RW and one JLN mutations have been found to take place.
