The common non-synonymous variant G38S of the KCNE1-(minK)-gene is not associated to QT interval in Central European Caucasians: results from the KORA study

Genetic Biomarkers of Antipsychotic-Induced Prolongation of the QT Interval in Patients with Schizophrenia

Antipsychotics (AP) induced prolongation of the QT interval in patients with schizophrenia (Sch) is an actual interdisciplinary problem as it increases the risk of sudden death syndrome. Long QT syndrome (LQTS) as a cardiac adverse drug reaction is a multifactorial symptomatic disorder, the development of which is influenced by modifying factors (APs' dose, duration of APs therapy, APs polytherapy, and monotherapy, etc.) and non-modifying factors (genetic predisposition, gender, age, etc.). The genetic predisposition to AP-induced LQTS may be due to several causes, including causal mutations in the genes responsible for monoheme forms of LQTS, single nucleotide variants (SNVs) of the candidate genes encoding voltage-dependent ion channels expressed both in the brain and in the heart, and SNVs of candidate genes encoding key enzymes of APs metabolism. This narrative review summarizes the results of genetic studies on AP-induced LQTS and proposes a new personalized approach to assessing the risk of its development (low, moderate, high). We recommend implementation in protocols of primary diagnosis of AP-induced LQTS and medication dispensary additional observations of the risk category of patients receiving APs, deoxyribonucleic acid profiling, regular electrocardiogram monitoring, and regular therapeutic drug monitoring of the blood APs levels.

Latent pathogenicity of the G38S polymorphism of KCNE1 K+ channel modulator

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.

Abnormal repolarization dynamics in a patient with KCNE1(G38S) who presented with torsades de pointes

Risk of G38S, major KCNE1 polymorphism [KCNE1(G38S)], for long QT syndrome (LQTS) remains unclear. A 72-year-old woman was admitted with recurrent torsades de pointes (TdP). She had remarkable QT prolongation (corrected QT interval 568 ms) under conditions of hypokalemia and hypomagnesemia. After correction of this electrolytic imbalance, TdP was suppressed and metoprolol was started. The QT-RR slope in 24-hour Holter electrocardiogram was steep and this enhanced bradycardia-dependent QT prolongation was similar to that in LQTS. She carried KCNE1(G38S). Patients with KCNE1(G38S) could have similar potential risk of ventricular arrhythmia as with LQTS. Analysis of QT-RR relationship could also evaluate the latent arrhythmogenicity of KCNE1(G38S).

Genetic variants in KCNE1, KCNQ1, and NOS1AP in sudden unexplained death during daily activities in Chinese Han population

Fifty-six sudden unexplained death (SUD) cases were collected from Chinese Han population, which occurred during daily activities and were autopsy negative in comprehensive postmortem autopsy. The coding exons of potassium channel genes KCNE1, KCNQ1, and nitric oxide synthase gene NOS1AP were sequenced. A synonymous mutation, KCNE1 F54F T>C was identified in 2 SUD cases, which was absent in the control subjects. Neither genotype nor allele frequencies of KCNE1 and KCNQ1 exhibited a significant difference between the SUD and control group. In contrast, the allele frequency (p = 2.7 × 10(-10)) and genotype frequency (p = 5.9 × 10(-7)) of rs3751284, and the genotype frequency (p = 2.9 × 10(-2)) of rs348624 in NOS1AP of SUD were significantly different from that of controls (p < 0.05). Our study suggested that rs3751284 and rs348624 might be susceptibility loci for SUD during daily activities. Larger sample sizes and further molecular studies are needed to confirm or exclude an effect of the NOS1AP SNPs on SUD risk.

Identification of Kv11.1 isoform switch as a novel pathogenic mechanism of long-QT syndrome

BACKGROUND

The KCNH2 gene encodes the Kv11.1 potassium channel that conducts the rapidly activating delayed rectifier current in the heart. The relative expression of the full-length Kv11.1a isoform and the C-terminally truncated Kv11.1a-USO isoform plays an important role in regulation of channel function. The formation of C-terminal isoforms is determined by competition between the splicing and alternative polyadenylation of KCNH2 intron 9. It is not known whether changes in the relative expression of Kv11.1a and Kv11.1a-USO can cause long-QT syndrome.

METHODS AND RESULTS

We identified a novel KCNH2 splice site mutation in a large family. The mutation, IVS9-2delA, is a deletion of the A in the AG dinucleotide of the 3' acceptor site of intron 9. We designed an intron-containing full-length KCNH2 gene construct to study the effects of the mutation on the relative expression of Kv11.1a and Kv11.1a-USO at the mRNA, protein, and functional levels. We found that this mutation disrupted normal splicing and resulted in exclusive polyadenylation of intron 9, leading to a switch from the functional Kv11.1a to the nonfunctional Kv11.1a-USO isoform in HEK293 cells and HL-1 cardiomyocytes. We also showed that IVS9-2delA caused isoform switch in the mutant allele of mRNA isolated from patient lymphocytes.

CONCLUSIONS

Our findings indicate that the IVS9-2delA mutation causes a switch in the expression of the functional Kv11.1a isoform to the nonfunctional Kv11.1a-USO isoform. Kv11.1 isoform switch represents a novel mechanism in the pathogenesis of long-QT syndrome.

Glycine/Serine polymorphism at position 38 influences KCNE1 subunit's modulatory actions on rapid and slow delayed rectifier K+ currents

BACKGROUND

 KCNE1 encodes a modulator of KCNH2 and KCNQ1 delayed rectifier K(+) current channels. KCNE1 mutations might cause long QT syndrome (LQTS) by impairing KCNE1 subunit's modulatory actions on these channels. There are major and minor polymorphismic KCNE1 variants whose 38(th) amino acids are glycine and serine [KCNE1(38G) and KCNE1(38S) subunits], respectively. Despite its frequent occurrence, the influence of this polymorphism on the K(+) channels' function is unclear.

METHODS AND RESULTS

 Patch-clamp recordings were obtained from human embryonic kidney -293T cells. KCNH2 channel current density in KCNE1(38S)-transfected cells was smaller than that in KCNE1(38G)-transfected cells by 34%. The voltage-sensitivity of the KCNQ1 channel current in KCNE1(38S)-transfected cells was lowered compared to that in KCNE1(38G)-transfected cells, with a +13mV shift in the half-maximal activation voltage. KCNH2 channel current density or KCNQ1 channel voltage-sensitivity was not different between KCNE1(38G)-transfected cells and cells transfected with both KCNE1(38G) and KCNE1(38S). Moreover, the KCNH2 channel current in KCNE1(38S)-transfected cells was more susceptible to E4031, a QT prolonging drug and a condition with hypokalemia, than that in KCNE1(38G)-transfected cells.

CONCLUSIONS

 Homozygous inheritance of KCNE1(38S) might cause a mild reduction of the delayed rectifier K(+) currents and might thereby increase an arrhythmogenic potential particularly in the presence of QT prolonging factors. By contrast, heterozygous inheritance of KCNE1(38G) and KCNE1(38S) might not affect the K(+) currents significantly.  (Circ J 2014; 78: 610-618).

Postmortem molecular analysis of KCNQ1, KCNH2, KCNE1 and KCNE2 genes in sudden unexplained nocturnal death syndrome in the Chinese Han population

The etiology of sudden unexplained nocturnal death syndrome (SUNDS) remains unclear. Previous studies have implicated that SUNDS is probably allelic to cardiac sodium channel diseases such as Brugada syndrome. The variation in cardiac potassium channels is the main genetic cause of inherited long QT syndrome (LQTS), which may manifest as syncope and sudden cardiac death without structural disease. We hypothesized that cardiac potassium channel disease may be responsible for certain Chinese SUNDS cases. Genotyping of 4 main LQTS-susceptibility genes (KCNQ1, KCNH2, KCNE1, and KCNE2) was performed here for the first time in SUNDS victims from the Chinese Han population to address the pathogenic cause of some SUNDS using polymerase chain reaction and direct DNA sequencing. 120 sporadic SUNDS cases were enrolled. Genomic DNA was extracted from blood samples. A total of 2 novel non-synonymous mutations and 3 previously reported arrhythmia susceptibility polymorphisms were identified in KCNQ1, KCNH2, KCNE1, and KCNE2. We concluded that the variants in KCNQ1, KCNH2, KCNE1 and KCNE2 genes may be correlated with the occurrence of part of SUNDS cases in southern China.

Genetic analysis of sudden unexplained death: a multidisciplinary approach

Each year infants, children and young adults die suddenly and unexpectedly. In many cases the cause of death can be elucidated by medico-legal autopsy, however, a significant number of these cases remain unexplained despite a detailed postmortem investigation and are labeled as sudden unexplained death (SUD). Post-mortem genetic testing, so called molecular autopsy, revealed that primary arrhythmogenic disorders including long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT) may account for a certain number of these cases. Because of the inheritance of these diseases, close relatives of the deceased may also at potential risk of carrying fatal cardiac disorders. Therefore, advanced diagnostic analyses, genetic counseling and interdisciplinary collaboration should be integral parts of clinical and forensic practice. In the present study, we performed mutation analyses of the major genes causing cardiac channelopathies in 15 SUD cases. In four cases we found putative pathogenic mutations in cardiac ion channel genes. Clinical and genetic examination of family members of SUD victims was also performed and affected family members were identified. This study demonstrates that molecular genetic screening needs to become an inherent part of the postmortem examination. This will enhance the ability of screening family members of SUD victims who may be at risk. The present data also illustrate that detection and follow up of familial cases of sudden death is challenging and requires a close multidisciplinary collaboration between different medical disciplines, with great responsibility for the forensic pathologist.

Trafficking of an endogenous potassium channel in adult ventricular myocytes

The roles of several small GTPases in the expression of an endogenous potassium current, I(to,f), in adult rat ventricular myocytes have been investigated. The results indicate that forward trafficking of newly synthesized Kv4.2, which underlies I(to,f) in these cells, requires both Rab1 and Sar1 function. Expression of a Rab1 dominant negative (DN) reduced I(to,f) current density by roughly one-half relative to control, mCherry-transfected myocytes. Similarly, expression of a Sar1DN nearly halved I(to,f) current density. Rab11 is not essential to trafficking of Kv4.2, as expression of a Rab11DN had no effect on I(to,f) over the time frames investigated here. In a process dependent on intact endoplasmic reticulum (ER)-to-Golgi transport, however, overexpression of wild-type Rab11 resulted in a doubling of I(to,f) density; block of ER-to-Golgi traffic by Brefeldin A completely abrogated the effect. Also implicated in the trafficking of Kv4.2 are Rab5 and Rab4. Rab5DN expression increased endogenous I(to,f) by two- to threefold, nonadditively with inhibition of dynamin-dependent endocytosis. And, in a phenomenon similar to that previously reported for myoblast-expressed Kv1.5, Rab4DN expression roughly doubled endogenous peak transient currents. Colocalization experiments confirmed the involvement of Rab4 in postinternalization trafficking of Kv4.2. There was little role evident for the lysosome in the degradation of internalized Kv4.2, as overexpression of neither wild-type nor DN isoforms of Rab7 had any effect on I(to,f). Instead, degradation may depend largely on the proteasome; the proteasome inhibitor MG132 significantly increased I(to,f) density.

Tox-database.net: a curated resource for data describing chemical triggered in vitro cardiac ion channels inhibition

BACKGROUND

Drugs safety issues are now recognized as being factors generating the most reasons for drug withdrawals at various levels of development and at the post-approval stage. Among them cardiotoxicity remains the main reason, despite the substantial effort put into in vitro and in vivo testing, with the main focus put on hERG channel inhibition as the hypothesized surrogate of drug proarrhythmic potency. The large interest in the IKr current has resulted in the development of predictive tools and informative databases describing a drug's susceptibility to interactions with the hERG channel, although there are no similar, publicly available sets of data describing other ionic currents driven by the human cardiomyocyte ionic channels, which are recognized as an overlooked drug safety target.

DISCUSSION

The aim of this database development and publication was to provide a scientifically useful, easily usable and clearly verifiable set of information describing not only IKr (hERG), but also other human cardiomyocyte specific ionic channels inhibition data (IKs, INa, ICa).

SUMMARY

The broad range of data (chemical space and in vitro settings) and the easy to use user interface makes tox-database.net a useful tool for interested scientists. DATABASE URL: http://tox-database.net.

An Examination of KCNE1 Mutations and Common Variants in Chronic Tinnitus

Chronic tinnitus is a highly prevalent and often incapacitating condition frequently associated with sensorineural hearing loss. While its etiology remains incompletely understood there is a growing awareness of genetic factors that predispose to, or aggravate chronic tinnitus. Candidate genes for the disorder include KCNE1, a potassium channel subunit gene that has been implicated in maturation defects of central vestibular neurons, in Menière's disease, and in noise-induced hearing loss. 201 Caucasian outpatients with a diagnosis of chronic tinnitus were systematically screened for mutations in the KCNE1 open reading frame and in the adjacent sequence by direct sequencing. Allele frequencies were determined for 46 known variants, plus two novel KCNE1 mutations. These comprised one missense substitution (V47I) in the highly conserved region encoding the KCNE1 transmembrane domain, and one rare variant in the gene's 3'UTR. When genotypes were grouped assuming dominance of the minor alleles, no significant genotype or compound genotype effects were observed on tinnitus severity. The newly identified V47I substitution argues in favor of an enlarged spectrum of mutations in hearing disorders. However, with regard to allele frequencies in healthy control populations from earlier studies, more common KCNE1 variants are unlikely to play a major role in chronic tinnitus. Further investigations are invited to address variation in additional channel subunits as possible risk factors in tinnitus.

S38G single-nucleotide polymorphism at the KCNE1 locus is associated with heart failure

BACKGROUND

Prolongation of the action potential duration, whose major determinants are the delayed-rectifier potassium currents, is a hallmark of failing ventricular myocardium. Genetic variants in the KCNE1 gene, encoding for the beta-subunit (minK) of a slowly activated cardiac potassium channel (I(ks)), may impair myocardial repolarization. Experimental data demonstrated a higher KCNE1 expression in heart failure (HF).

OBJECTIVE

The purpose of this study was to investigate the association between a KCNE1 S38G single-nucleotide polymorphism (SNP) and HF.

METHODS

We genotyped 197 out of 323 previously investigated patients and 352 healthy controls comparable for age and sex. This study was replicated in 186 HF patients and in 200 healthy subjects comparable for age and sex and recruited from the Department of Cardiovascular Medicine of the National Research Council, Pisa, Italy.

RESULTS

A significant difference in genotype distribution and allele frequency between patients and controls was observed for the KCNE1 S38G SNP (P = .002 and P = .0008, respectively). The KCNE1 38G variant was associated with a significant predisposition to HF under a dominant (odds ratio [OR] = 2.22 [1.23-3.28]; P = .008) and additive (OR = 2.13 [1.09-4.15]; P = .03) model, after adjustment for age, sex, and traditional cardiovascular risk factors. No difference in genotype distribution and allele frequency for the KCNE1 S38G SNP according to functional New York Heart Association class was found (P = .4 and P = .3, respectively). In the HF replication study, the KCNE1 38G allele frequency was significantly higher in comparison with that observed in the control population (38G = 0.59 vs. 0.49; P = .004). The 38G allele was associated with HF predisposition under the recessive (OR [95% confidence interval (CI)] = 2.49 [1.45-4.29]; P = .001) and additive models (OR [95% CI] = 2.63 [1.29-5.35]; P = .008), after adjustment for traditional risk factors.

CONCLUSION

KCNE1 S38G SNP is associated with HF predisposition in two study populations. Nevertheless, further studies performed in larger populations and aimed to better define the role of this locus are required.

Positive selection at codon 38 of the human KCNE1 (= minK) gene and sporadic absence of 38Ser-coding mRNAs in Gly38Ser heterozygotes

Background

KCNE1 represents the regulatory beta-subunit of the slowly activating delayed rectifier potassium channel (IKs). Variants of KCNE1 have repeatedly been linked to the long-QT syndrome (LQTS), a disorder which predisposes to deafness, ventricular tachyarrhythmia, syncope, and sudden cardiac death.

Results

We here analyze the evolution of the common Gly38Ser variant (rs1805127), using genomic DNAs, complementary DNAs, and HEK293-expressed variants of altogether 19 mammalian species. The between species comparison reveals that the human-specific Gly38Ser polymorphism evolved under strong positive Darwinian selection, probably in adaptation to specific challenges in the fine-tuning of IKs channels. The involved amino acid exchanges (Asp > Gly, Gly > Ser) are moderately radical and do not induce apparent changes in posttranslational modification. According to population genetic analyses (HapMap phase II) a heterozygote advantage accounts for the maintenance of the Gly38Ser polymorphism in humans. On the other hand, the expression of the 38Ser allele seems to be disadvantageous under certain conditions, as suggested by the sporadic deficiency of 38Ser-coding mRNAs in heterozygote Central Europeans and the depletion of homozygotes 38Ser in the Yoruban sample.

Conclusion

We speculate that individual differences in genomic imprinting or genomic recoding might have contributed to conflicting results of recent association studies between Gly38Ser polymorphism and QT phenotype. The findings thus highlight the relevance of mRNA data in future association studies of genotypes and clinical disorders. To the best of our knowledge, they moreover provide first time evidence for a unique pattern; i.e. coincidence of positive Darwinian selection and polymorphism with a sporadically suppressed expression of one allele.

Cardiac ankyrins in health and disease

Ankyrins are critical components of ion channel and transporter signaling complexes in the cardiovascular system. Over the past 5 years, ankyrin dysfunction has been linked with abnormal ion channel and transporter membrane organization and fatal human arrhythmias. Loss-of-function variants in the ankyrin-B gene (ANK2) cause "ankyrin-B syndrome" (previously called type 4 long QT syndrome), manifested by a complex cardiac phenotype including ventricular arrhythmias and sudden cardiac death. More recently, dysfunction in the ankyrin-B-based targeting pathway has been linked with a highly penetrant and severe form of human sinus node disease. Ankyrin-G (a second ankyrin gene product) is required for normal expression, membrane localization, and biophysical function of the primary cardiac voltage-gated sodium channel, Na(v)1.5. Loss of the ankyrin-G/Na(v)1.5 interaction is associated with human cardiac arrhythmia (Brugada syndrome). Finally, in the past year ankyrin dysfunction has been associated with more common arrhythmia and cardiovascular disease phenotypes. Specifically, large animal studies reveal striking remodeling of ankyrin-B and associated proteins following myocardial infarction. Additionally, the ANK2 locus has been linked with QT(c) interval variability in the general human population. Together, these findings identify a host of unanticipated and exciting roles for ankyrin polypeptides in cardiac function. More broadly, these findings illustrate the importance of local membrane organization for normal cardiac physiology.

Common candidate gene variants are associated with QT interval duration in the general population

OBJECTIVES

QT interval prolongation is associated with increased risk of sudden cardiac death at the population level. As 30-40% of the QT-interval variability is heritable, we tested the association of common LQTS and NOS1AP gene variants with QT interval in a Finnish population-based sample.

METHODS

We genotyped 12 common LQTS and NOS1AP genetic variants in Health 2000, an epidemiological sample of 5043 Finnish individuals, using Sequenom MALDI-TOF mass spectrometry. ECG parameters were measured from digital 12-lead ECGs and QT intervals were adjusted for age, gender and heart rate with a nomogram (Nc) method derived from the present study population.

RESULTS

The KCNE1 D85N minor allele (frequency 1.4%) was associated with a 10.5 ms (SE 1.6) or 0.57 SD prolongation of the adjusted QT(Nc) interval (P=3.6 x 10(-11)) in gender-pooled analysis. In agreement with previous studies, we replicated the association with QT(Nc) interval with minor alleles of KCNH2 intronic SNP rs3807375 [1.6 ms (SE 0.4) or 0.08 SD, P=4.7 x 10(-5)], KCNH2 K897T [-2.6 ms (SE 0.5) or -0.14 SD, P=2.1 x 10(-7)] and NOSA1P variants including rs2880058 [4.0 ms (SE 0.4) or 0.22 SD, P=3.2 x 10(-24)] under additive models.

CONCLUSIONS

We demonstrate that each additional copy of the KCNE1 D85N minor allele is associated with a considerable 10.5 ms prolongation of the age-, gender- and heart rate-adjusted QT interval and could thus modulate repolarization-related arrhythmia susceptibility at the population level. In addition, we robustly confirm the previous findings that three independent KCNH2 and NOSA1P variants are associated with adjusted QT interval.

Common variants at ten loci modulate the QT interval duration in the QTSCD Study

The QT interval, a measure of cardiac repolarization, predisposes to ventricular arrhythmias and sudden cardiac death (SCD) when prolonged or shortened. A common variant in NOS1AP is known to influence repolarization. We analyze genome-wide data from five population-based cohorts (ARIC, KORA, SardiNIA, GenNOVA and HNR) with a total of 15,842 individuals of European ancestry, to confirm the NOS1AP association and identify nine additional loci at P < 5 x 10(-8). Four loci map near the monogenic long-QT syndrome genes KCNQ1, KCNH2, SCN5A and KCNJ2. Two other loci include ATP1B1 and PLN, genes with established electrophysiological function, whereas three map to RNF207, near LITAF and within NDRG4-GINS3-SETD6-CNOT1, respectively, all of which have not previously been implicated in cardiac electrophysiology. These results, together with an accompanying paper from the QTGEN consortium, identify new candidate genes for ventricular arrhythmias and SCD.

Sudden cardiac death: The larger problem... The larger genome

This perspective considers progress in understanding how genetic influences modulate susceptibility to lethal ventricular arrhythmias in cardiac patients and the population at large, as opposed to those with rare inherited arrhythmic conditions, such as the Long-QT and Brugada syndromes. It addresses largely unresolved issues, such as how important these effects may be and what we know of underlying mediators and pathways. Attention is given to newly revealed mechanisms of genomic function and the problem of identifying new susceptibility genes and targets useful in developing improved strategies for sudden death prevention.

Identification of a common variant at the NOS1AP locus strongly associated to QT-interval duration

QT-interval prolongation is an electrophysiologic phenomenon associated with sudden cardiac death. The QT-interval in the general population is approximately 35% heritable. In genome-wide association studies, a common variant (rs10494366T > G) within the nitric oxide synthase 1 adaptor protein (NOS1AP) gene was identified and consistently associated with QT-interval duration. Yet, the causal variant remains unclear. Therefore, we performed fine mapping of the association of the NOS1AP locus with QT-interval within the Rotterdam Study, a population-based, prospective cohort study of individuals of > or =55 years of age. First, we tested the association of single-nucleotide polymorphisms (SNPs) in or within +/-100 kb of the NOS1AP gene with QT-interval duration, using sex-specific unstandardized residuals after regression on age and RR-interval, in 385 individuals using the combined set of SNPs present in the Affymetrix 500k and Illumina 550k chip arrays. Subsequently, we examined correspondence of the association signals in 4606 individuals using the Illumina 550k array. A C-to-T SNP at chromosome 1 position 160300514 (rs12143842, T-allele frequency = 24%) was associated with a QT-interval duration increase of 4.4 ms per additional T-allele (P = 4.4 x 10(-28)). For comparison, the most strongly associated variant to date, rs10494366T > G, was associated with a 3.5 ms increase (P = 1.6 x 10(-23)) per additional G-allele. None of the inferred haplotypes showed a stronger effect than the individual rs12143842C > T SNP. In conclusion, we found rs12143842 6 kb upstream distance of NOS1AP to be more strongly associated to QT-interval duration than rs10494366T > G. Functional analysis of this marker is warranted.

A KCNQ1 V205M missense mutation causes a high rate of long QT syndrome in a First Nations community of northern British Columbia: a community-based approach to understanding the impact

PURPOSE

Hereditary long QT syndrome is named for a prolonged QT interval reflecting predisposition to ventricular arrhythmias and sudden death. A high rate in a remote, northern Canadian First Nations community was brought to attention.

METHODS

Two severely affected index cases and 122 relatives were ascertained using community-based participatory research principles. Genetic sequencing of five known genes responsible for long QT syndrome was carried out on the index cases, leading to the identification of a novel missense mutation. Functional properties of the identified mutation were studied in transfected mouse ltk- cells using whole cell patch clamp techniques. Corrected QT interval measurements were obtained from participants and subsequent genotyping of relatives was carried out.

RESULTS

In the two index cases, a novel missense mutation (V205M) was identified in the S3 transmembrane helix of KvLQT1, the pore forming domain of the IKs channel complex. In transfected mouse ltk-cells the V205M mutation suppressed IKs by causing a dramatic depolarizing shift in activation voltage coupled with acceleration of channel deactivation. Twenty-two mutation carriers had a significantly higher mean corrected QT interval than noncarriers (465 +/- 28 milliseconds vs. 434 +/- 26 milliseconds, P < 0.0001); however, 30% of carriers had a corrected QT interval below 440 milliseconds.

CONCLUSION

A novel KCNQ1 mutation in this founder population likely confers increased susceptibility to arrhythmias because of decreased IKs current. Even with a common mutation within a relatively homogenous population, clinical expression remains variable, exemplifying the multifactorial nature of long QT syndrome, and supporting the difficulty of definitive diagnosis without genetic testing. A community participatory approach enabled a comprehensive evaluation of the impact.

Effect of common KCNE1 and SCN5A ion channel gene variants on T-wave alternans, a marker of cardiac repolarization, during clinical exercise stress test: the Finnish Cardiovascular Study

T-wave alternans (TWA) in electrocardiography (ECG) is a marker of cardiac repolarization, the molecular regulation of which is incompletely understood. High TWA and prolonged QT intervals are both associated with ventricular arrhythmias and sudden death. Therefore, we tested the hypothesis of whether the same mutations that influence the QT interval also affect TWA variation. We examined the effect of 3 ion channel gene single nucleotide polymorphisms (SNPs), rs1805127, rs727957 KCNE1, and rs1805124 SCN5A, on TWA during a clinical exercise test. A total of 2008 subjects from the Finnish Cardiovascular Study underwent an exercise test with online ECG recording. TWA was measured by using the time-domain, modified moving average method. Maximum values at rest, during maximal exercise, and during recovery were used as outcome measures in statistical analysis. Moreover, 4-year survival data were collected and ion channel SNPs were determined. TWA was lowest in subjects with the TT genotype of rs1805127 during all phases of the exercise test (RANOVA main effect for genotype, P = 0.018). The result remained significant after adjustment for age, existing coronary heart disease, and beta-blocker medication status (RANCOVA, P = 0.035). Of the polymorphisms studied, only rs1805127 had a significant association with mortality (P = 0.047). The most common G-C haplotype, formed by rs727957 and rs1805127, was associated with TWA (RANOVA, P = 0.007) but not with mortality. The rs1805124 polymorphism was not associated with TWA. The common KCNE1 gene variant rs1805127 is associated with TWA during an exercise test in a Finnish population, which provides additional evidence that KCNE1 genetics may influence cardiac repolarization and cardiovascular mortality.

Gender and effects of a common genetic variant in the NOS1 regulator NOS1AP on cardiac repolarization in 3761 individuals from two independent populations

BACKGROUND

A longer heart-rate corrected QT interval (QTc) is associated with increased risk of ventricular arrhythmias. Women have longer resting QTc and are more likely than men to develop drug-induced QT prolongation. Recent studies have shown association between resting QTc and a common variant (rs10494366) of the NOS1 regulator, NOS1AP. We investigated the association between rs10494366 in NOS1AP and QTc, and assessed gender-specific NOS1AP associations with QTc during rest and after exercise.

METHODS

We investigated the SNP associations with resting QTc in 919 women and 918 men from 504 representative families in the UK GRAPHIC study, and with QTc at rest and at 3 min recovery after exercise in 699 women and 1225 men referred for exercise testing in the Finnish FINCAVAS study.

RESULTS

In the GRAPHIC study the minor allele (G) of the NOS1AP SNP rs10494366 prolonged QTc by 4.59 ms (95% CI 2.77-6.40; P = 7.63/10(7)) in women, but only by 1.62 ms (95% CI -0.15 to 3.38; P = 0.073) in men (gender-SNP interaction term P = 0.025). In the FINCAVAS study the G allele significantly prolonged QTc in both women (P = 0.0063) and men (P = 0.0043) at 3 min recovery after exercise, but at rest an association was only seen in women (P = 0.020 excluding outliers).

CONCLUSIONS

A common NOS1AP variant prolongs QTc with a difference between genders. Further studies should aim to confirm this finding and to assess whether NOS1AP genotype influences the risk of drug-induced QT prolongation and risk of consequent arrhythmias.

Confirmation of associations between ion channel gene SNPs and QTc interval duration in healthy subjects

Population-based association studies have identified several polymorphic variants in genes encoding ion channel subunits associated with the electrocardiographic heart-rate-corrected QT (QTc) length in healthy populations of Caucasian origin (KCNH2 rs1,805,123 (K897 T) and rs3,815,459, SCN5A rs1,805,126 (D1,819D), 1,141-3 C>A, rs1,805,124 (H558R), and IVS24+116 G>A, KCNQ1 rs757,092, KCNE1 IVS2-128 G>A and rs1,805,127 (G38S), and KCNE2 rs2,234,916 (T8A)). However, few of these results have been replicated in independent populations. We tested the association of SNPs KCNQ1 rs757,092, KCNH2 rs3,815,459, SCN5A IVS24+116 G>A, KCNE1 IVS2-128 G>A and KCNE2 rs2,234,916 with QTc length in two groups of 200 subjects presenting the shortest and the longest QTc from a cohort of 2,008 healthy subjects. All polymorphisms were in Hardy-Weinberg equilibrium in both groups. The minor allele SCN5A IVS24+116 A was more frequent in the group of subjects with the shortest QTc, whereas the minor alleles KCNQ1 rs757,092 G and KCNH2 rs3,815,459 A were more frequent in the group with the longest QTc. There was no significant difference for KCNE1 IVS2-128 G>A and KCNE2 rs2,234,916 between the two groups. Haplotype analysis showed a twofold increased risk of QTc lengthening for carriers of the haplotype, combining alleles C and A of the two common KCNE1 SNPs, IVS2-129 C>T (rs2,236,609) and rs1,805,127 (G38S), respectively. In conclusion, our study confirms the reported associations between QTc length and KCNQ1 rs757,092 and KCNH2 rs3,815,459.