Genetic and environmental sources of QT interval variability in Israeli families: the kibbutz settlements family study

Heritability in genetic heart disease: the role of genetic background

Background

Mutations in genes encoding ion channels or sarcomeric proteins are an important cause of hereditary cardiac disease. However, the severity of the resultant disease varies considerably even among those with an identical mutation. Such clinical variation is often thought to be explained largely by differences in genetic background or 'modifier genes'. We aimed to test the prediction that identical genetic backgrounds result in largely similar clinical expression of a cardiac disease causing mutation, by studying the clinical expression of mutations causing cardiac disease in monozygotic twins.

Methods

We compared first available clinical information on 46 monozygotic twin pairs and 59 control pairs that had either a hereditary cardiomyopathy or channelopathy.

Results

Despite limited power of this study, we found significant heritability for corrected QT interval (QTc) in long QT syndrome (LQTS). We could not detect significant heritability for structural traits, but found a significant environmental effect on thickness of the interventricular septum in hypertrophic cardiomyopathy.

Conclusions

Our study confirms previously found robust heritability for electrical traits like QTc in LQTS, and adds information on low or lacking heritability for structural traits in heritable cardiomyopathies. This may steer the search for genetic modifiers in heritable cardiac disease.

A study of Kibbutzim in Israel reveals risk factors for cardiometabolic traits and subtle population structure

Genetic studies in isolated populations often increase power for identifying loci associated with complex diseases and traits. We present here the Kibbutzim Family Study (KFS), aimed at investigating the genetic basis of cardiometabolic traits in extended Israeli families characterized by long-term social stability and a homogeneous environment. Extensive information on cardiometabolic traits, as well as genome-wide genotypes, were collected on 901 individuals. We observed that most KFS participants were of Ashkenazi Jewish (AJ) genetic origin, confirmed a recent severe bottleneck in the AJ recent history, and detected a subtle within-AJ population structure. Focusing on genetic variants relatively common in the KFS but very rare in Europeans, we observed that AJ-enriched variants appear in cancer-related pathways more than expected by chance. We conducted an association study of the AJ-enriched variants against 16 cardiometabolic traits, and found seven loci (24 variants) to be significantly associated. The strongest association, which we also replicated in an independent study, was between a variant upstream of MSRA (frequency ≈1% in the KFS and nearly absent in Europeans) and weight (P = 3.6∙10-8). In conclusion, the KFS is a valuable resource for the study of the population genetics of Israel as well as the genetics of cardiometabolic traits.

Differences in the electrocardiographic QT interval of various breeds of athletic horses during rest and exercise

OBJECTIVES

Quantitative measurements of cardiac repolarization, defined as the electrocardiographic QT interval, have important diagnostic implications in humans, as irregularities can trigger potentially fatal ventricular tachyarrhythmia. In both humans and horses, cardiac repolarization is influenced to some extent by heart rate, age, body weight (BW), sex, autonomic tone, and environment. In horses, there is substantial inter-breed variation in size and training, and the aims of this study were therefore to determine the best model describing the QT to RR relationship in breeds of various athletic horses and to test for differences in the QT interval.

ANIMALS

Ten Icelandic horses, 10 Arabian horses, 10 Thoroughbreds, 10 Standardbreds, six Coldblood trotters, 10 Warmbloods (dressage) and 10 Warmbloods (show jumping). All horses were geldings.

METHODS

QT intervals were measured from resting to peak exercise level and plotted against RR intervals. Data points were fitted with relevant regression models, and the effect of breed, BW, and estimated exercise intensity was examined.

RESULTS

For all breeds in this study, the QT interval was best described as a function of RR by the piecewise linear regression model. The breed of horse had a significant effect on the model. There was no systematic effect of BW or estimated exercise intensity, but a high inter-horse variability was observed.

CONCLUSIONS

The equine QT interval should preferably be corrected for heart rate according to breed. In addition, the results indicate that equine studies of the QT interval must be designed to eliminate the influence of a large inter-horse variation.

Diurnal modulation and sources of variation affecting ventricular repolarization in Warmblood horses

OBJECTIVES

Irregularities in cardiac repolarization are known to predispose for arrhythmias and sudden cardiac death in humans. The QT interval is a quantitative measurement of repolarization, and clinically, the QTc (QT interval corrected for heart rate) and Tpeak to Tend intervals (TpTe) are used as repolarization markers. To support the use of these markers in horses, we sought to describe the possible influence of the environment, time of day, day-to-day effects, T wave conformation, age, body weight (BW), and horse-to-horse variation on repolarization measurements.

ANIMALS

12 Warmblood geldings, age 10.8 ± 4.8 years.

METHODS

Holter ECGs were performed on days 0, 7 and 14. Measures of RR, QT, QTp, QTc and TpTe intervals and T wave conformation were obtained each hour during the recordings. An ANCOVA analysis was performed to estimate diurnal variation and the sources of variation affecting these intervals.

RESULTS

Differences between individual horses were the largest source of repolarization variability although the environment had a significant effect on repolarization as well. Diurnal variation affected both the RR interval and the repolarization markers. The QT, QTc and TpTe intervals were prolonged on day 0. Biphasic T waves shortened the TpTe interval approximately 10 ms. Age and BW did not appear to affect repolarization.

CONCLUSIONS

Equine repolarization markers exhibit significant variation. Factors affecting repolarization measurements include horse-to-horse variation, diurnal variation, the environment, and T wave conformation. These factors must be considered if markers of equine repolarization are used diagnostically.

Timing of pre-dose baseline electrocardiograms in clinical trials: increased sampling over a prolonged baseline period worsens variance of QTc

BACKGROUND AND PURPOSE

The US Food and Drug Administration (US FDA) currently recommends recording of electrocardiograms (ECGs) prior to drug administration in thorough QT studies over an hour or more time to improve reliability of baseline ECG values. However, the baseline period is usually in the morning during a period of intense trial activity and rapid circadian change in QTc. The purpose of this study was to determine if the practice of recording an extended baseline does, in fact, decrease QTc variance at baseline.

METHODS

ECG data from three thorough QT studies (TQTS) in which three ECGs (commonly referred to as triplicates) were recorded at each of three pre-specified time points during the 60 to 90 minutes before drug administration were analyzed by determining the intra-subject and inter-subject standard deviation (SD) of QTcF (Fridericia-correct QT) for each of the three pre-drug time points and for the three time points combined.

RESULTS

QTcF was relatively normally distributed in each study. Intra-subject variability of QTcF was greater for the combined triplicate recordings than for the individual triplicates at baseline treatment time points in 39 of 42 cases (93%). This was the case in 48% of the comparisons in the inter-subject analysis.

CONCLUSIONS

The practice of recording three sets of triplicate ECGs over an hour or more before drug administration in a TQTS increases variability of baseline QTcF consistently in cross-over designed trials, and in roughly half of parallel comparisons. Higher variability suggests that the three-triplicate approach does not provide a more reliable baseline value. Less variability of QTcF can be obtained by simply recording one triplicate prior to drug administration. This principal may apply to other ECG and other physiological variables that have a monotonic circadian trend or that may be affected by intense trial activity during the pre-drug hour.

Genetics of sudden cardiac death caused by ventricular arrhythmias

Sudden cardiac death (SCD) resulting from ventricular tachyarrhythmia is a major contributor to mortality. Clinical management of SCD, currently based on clinical markers of SCD risk, can be improved by integrating genetic information. The identification of multiple disease-causing gene variants has already improved patient management and increased our understanding of the rare Mendelian diseases associated with SCD risk in the young, but marked variability in disease severity suggests that additional genetic modifiers exist. Next-generation DNA sequencing could be crucial to the discovery of SCD-associated genes, but large data sets can be difficult to interpret. SCD usually occurs in patients with an average age of 65 years who have complex cardiac disease stemming from multiple, common, acquired disorders. Heritable factors are largely unknown, but are likely to have a role in determining the risk of SCD in these patients. Numerous genetic loci have been identified that affect electrocardiogram indices, which are regarded as intermediate phenotypes for tachyarrhythmia. These loci could help to identify new molecules and pathways affecting cardiac electrical function. These loci are often located in intergenic regions, so our evolving understanding of the noncoding regulatory regions of the genome are likely to aid in the identification of novel genes that are important for cardiac electrical function and possibly SCD.

Common genetic variation modulating cardiac ECG parameters and susceptibility to sudden cardiac death

Sudden cardiac death (SCD) is a prevalent cause of death in Western societies. Genome-wide association studies (GWAS) conducted over the last few years have uncovered common genetic variants modulating risk of SCD. Furthermore, GWAS studies uncovered several loci impacting on heart rate and ECG indices of conduction and repolarization, as measures of cardiac electrophysiological function and likely intermediate phenotypes of SCD risk. We here review these recent developments and their implications for the identification of novel molecular pathways underlying normal electrophysiological function and susceptibility to SCD.

Analysis of genetic and non-genetic factors that affect the QTc interval in a Mongolian population: the GENDISCAN study

The QTc interval is a complex quantitative trait and a strong prognostic indicator of cardiovascular mortality in general, healthy people. The aim of this study was to identify non-genetic factors and quantitative trait loci that govern the QTc interval in an isolated Mongolian population. We used multiple regression analysis to determine the relationship between the QTc interval and non-genetic factors including height, blood pressure, and the plasma lipid level. Whole genome linkage analyses were performed to reveal quantitative trait loci for the QTc interval with 349 microsatellite markers from 1,080 Mongolian subjects. Among many factors previously known for association with the QTc interval, age, sex, heart rate, QRS duration of electrocardiogram and systolic blood pressure were also found to have influence on the QTc interval. A genetic effect for the QTc interval was identified based on familial correlation with a heritability value of 0.31. In a whole genome linkage analysis, we identified the four potential linkage regions 7q31-34, 5q21, 4q28, and 2q36.

Familial aggregation and heritability of electrocardiographic intervals and heart rate in a rural Chinese population

BACKGROUND

Estimates of the genetic influences on electrocardiographic (ECG) parameters are inconsistent in previous reports, and no such studies have been performed in China. So we estimated genetic contributions to PR and QRS intervals and the rate-adjusted QT interval (Bazett's QTc) in a Chinese rural population.

METHODS

A total of 2909 subjects from 847 families were enrolled in the current study. Genetic contributions to ECG parameters were estimated in two ways: correlation coefficients among family members (father-mother, parent-offspring, first sibling-other sibling) and the heritability of each of the ECG parameters.

RESULTS

Our results showed significant correlations among family members on theses parameters: the correlation coefficients for PR interval, QRS duration, QTc interval, and HR, between parent-sibling, and sibling-sibling were 0.17 and 0.13, 0.18 and 0.23, 0.22 and 0.28, 0.19 and 0.18, respectively. The heritability for PR interval, QRS duration, QTc interval, and HR were estimated as 0.34, 0.43, 0.40, and 0.34, respectively.

CONCLUSION

Genetic factors, together with the environmental and other cofactors contribute no more than 60% to the variance of the ECG intervals, supporting the concept that multiple factors, including gene-gene and gene-environment interactions could influence ECG interval phenotypes, and genetic factors play a major role.

Common variation in NOS1AP and KCNH2 genes and QT interval duration in young adults. The Cardiovascular Risk in Young Finns Study

BACKGROUND

Common genetic variants in the nitric oxide synthase 1 adaptor protein gene (NOS1AP) and in the HERG potassium channel gene (KCNH2) have been associated with cardiac repolarization in middle-aged and elderly subjects.

AIM

We examined the relation between these variants and QT interval duration in a population of healthy young adults.

METHODS

We measured QT interval duration and genotyped rs10494366 T>G (NOS1AP gene, n=1,842) and rs1805123 A>C (KCNH2 gene, n=1,894) in subjects aged 24-39 years.

RESULTS

The NOS1AP variant was significantly related with heart rate-corrected QT interval duration (QTc). Additive regression model adjusting for age, sex, systolic blood pressure, body mass index, alcohol use, and smoking indicated that the G allele was associated with a 3.2 ms (95% confidence interval (CI) 1.7-4.6 ms, P<0.0001) increase in QTc interval duration for each additional copy. The KCNH2 variant was not significantly related with QTc interval duration in the study sample.

CONCLUSION

These findings provide evidence from a population of healthy young adults that a common variation in the NOS1AP gene influences cardiac repolarization within the normal physiological range. Further studies are warranted to investigate the effects of this variant on sudden cardiac death and ventricular arrhythmias.

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.

Genetische Determinanten des EKG

Schon bald nach der Erfindung des EKG wurden die hohen Heritabilitäten vieler EKG-Parameter erkannt. Seit etwa einer Dekade wird intensiv an der Aufklärung zugrunde liegender genetischer Varianten gearbeitet, mit der Einführung genomweiter Assoziationsstudien steht dafür nun auch eine adäquate Methode zur Verfügung. Die molekulare Identifizierung und Charakterisierung bisher unbekannter herzrhythmusassoziierter Gene und Genvarianten verspricht nicht nur eine Vertiefung unseres Verständnisses der kardialen Elektrophysiologie, sondern auch eine Option auf bessere therapeutische und präventive Strategien für Arrhythmien und den plötzlichen Herztod.

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.

Association between angiotensin-converting enzyme gene polymorphisms and QT duration in a multiethnic population in Hawaii

OBJECTIVES

Recent studies have suggested that heart-rate corrected QT interval (QTc) in normal populations may be influenced by genetic factors. We report findings of a study of the relationship between QTc, increased QTc (> 440 ms) and angiotensin-converting enzyme (ACE) genotype in a multiethnic, population-based study completed in rural Hawaii.

METHODS

Blood samples were obtained while fasting and after an oral glucose challenge from 1452 individuals between 1997 and 2000. The clinical examination included an electrocardiogram. Medical histories, behavioral and socio-demographic information were obtained during the interview. Ethnicity was estimated by self-report. The insertion/deletion (I/D) polymorphism in intron 16 of the ACE gene was determined by polymerase chain reaction (PCR) from a random sample of 588 participants. Multiple linear and logistic regression was used to test for associations between QTc and ACE gene polymorphisms.

RESULTS

The overall crude prevalence of increased QTc was 21.2%. The prevalence of increased QTc was lowest among those with ACE DD genotype, and highest among those with ACE insertion/insertion (II) genotype. The adjusted odds ratio for increased QTc was 2.29 (95% CI 1.02-5.12) and 3.61 (95% CI 1.60-8.13) for ID and II genotypes, respectively, compared to the DD genotype. The test for trend was highly significant (p < 0.001).

CONCLUSIONS

The ACE insertion allele was associated with increased prevalence of prolonged QTc independent of ethnicity, age, gender, and BMI. These findings may implicate the ACE gene as an important genetic risk factor for cardiovascular disease morbidity and mortality.

Possible association of the human KCNE1 (minK) gene and QT interval in healthy subjects: evidence from association and linkage analyses in Israeli families

QT interval prolongation is associated with increased risk of sudden and non-sudden cardiac death. Potassium channel gene variants are associated with inherited long QT syndromes. Using linkage and association analyses, we investigated whether variants in the potassium channel subunit KCNE1 are associated with QTc intervals in an unselected population sample of 80 kindreds living in kibbutz settlements in Israel. Variance-component linkage analysis revealed weak evidence of linkage of KCNE1 polymorphisms with QTc intervals. Family-based association analysis showed a significant association between the G38S polymorphism and QTc interval. Further quantitative trait association analysis demonstrated a significant residual heritability component (h(2)= 0.33), and that the effect of the G38S variant allele is modified by gender. Estimated maximum likelihood parameters from these models indicated that male gender, age, hypertension, diabetes, hypercholesterolemia, fibrinogen and BMI were positively associated with QTc interval; level of education and cigarette smoking showed an inverse association. Both erythrocyte membrane n-6 and n-3 fatty acids showed a significant inverse association with QTc interval. While more than 15.8% of QTc variability was contributed by covariates, another 4.7% was explained by dietary factors, the G38S polymorphism explained 2.2%, and approximately 36% was explained by polygenes. An in silico analysis showed also that the novel V80 SNP, another KCNE1 synonymous variant, abolishes the recognition for a splicing enhancer, which may lead to an increased effect of the G38S mutation. These results demonstrate that, in addition to polygenic background, dietary factors and other covariables, the KCNE1 G38S variant is involved in determining QTc levels in this population-based sample of families.

Prevalence and risk factors for prolonged QTc in a multiethnic cohort in rural Hawaii

BACKGROUND

Few studies have examined the biochemical risk factors for prolonged QTc, a predictor of mortality in numerous studies. We report on the prevalence and risk factors for prolonged QTc in a multiethnic population in rural Hawaii.

METHODS

Electrocardiograms were collected from 1415 participants in a cross-sectional survey. The QT interval lengths were corrected for heart rate using Bazett's formula. Linear and logistic regression models were used to examine associations between various cardiovascular risk factors with QTc.

RESULTS

Among the CVD risk factors examined, only age, gender, 2-h glucose, and systolic blood pressure (SBP) were independently associated with QTc interval length. Significant ethnic differences in prevalence were also observed, which persisted after controlling for other risk factors.

CONCLUSIONS

Significant associations between prolonged QTc and ethnic ancestry, but not cholesterol or triglyceride levels, suggest that genetic factors may play a more important role in determining QTc interval length than conventional biochemical and metabolic CVD risk factors.

Common Variants in Myocardial Ion Channel Genes Modify the QT Interval in the General Population

Altered myocardial repolarization is one of the important substrates of ventricular tachycardia and fibrillation. The influence of rare gene variants on repolarization is evident in familial long QT syndrome. To investigate the influence of common gene variants on the QT interval we performed a linkage disequilibrium based SNP association study of four candidate genes. Using a two-step design we analyzed 174 SNPs from the KCNQ1, KCNH2, KCNE1, and KCNE2 genes in 689 individuals from the population-based KORA study and 14 SNPs with results suggestive of association in a confirmatory sample of 3277 individuals from the same survey. We detected association to a gene variant in intron 1 of the KCNQ1 gene (rs757092, +1.7 ms/allele, P =0.0002) and observed weaker association to a variant upstream of the KCNE1 gene (rs727957, +1.2 ms/allele, P =0.0051). In addition we detected association to two SNPs in the KCNH2 gene, the previously described K897T variant (rs1805123, −1.9 ms/allele, P =0.0006) and a gene variant that tags a different haplotype in the same block (rs3815459, +1.7 ms/allele, P =0.0004). The analysis of additive effects by an allelic score explained a 10.5 ms difference in corrected QT interval length between extreme score groups and 0.95% of trait variance ( P <0.00005). These results confirm previous heritability studies indicating that repolarization is a complex trait with a significant heritable component and demonstrate that high-resolution SNP-mapping in large population samples can detect and fine map quantitative trait loci even if locus specific heritabilities are small.

Differences between ventricular repolarization in men and women: description, mechanism and implications

The purpose of this review article is to discuss the differences between ventricular repolarization in males and females in terms of morphology, possible mechanism, and practical significance. The interest in the subject increased when it became known that in comparison to men, women have a higher incidence of torsade de pointes (tdp) and a greater lengthening of QT-interval after administration of class III antiarrhythmic drugs. Before puberty, the QT intervals and the patterns of ventricular repolarization in boys and girls are similar. At puberty, in boys the QT interval shortens, and a typical male pattern of ventricular repolarization develops. This pattern is characterized by a higher amplitude of the J-point, a shorter and steeper ST segment course, a steeper ascent, and a higher amplitude of the T wave. This pattern is prevalent in >90% of young males. With increasing age the prevalence of the male pattern in males declines gradually and drops to 14% in the oldest age group. The rise and fall of the prevalence of the male pattern appears to parallel the rise and decline of testosterone in males. The female pattern of ventricular repolarization is prevalent in about 80% of females in all age groups. The hormonal effects on ventricular repolarization have been studied in normal and castrated rabbits of both sexes. The available evidence indicates that the females have greater divergence of L calcium current among different layers of the myocardium and a lower density of the repolarizing Kr and Ks currents. The clinical significance of the repolarization differences among genders remains to be determined. Of particular interest is the question whether the males with female pattern are at the same risk of tdp as the females or whether the females with male pattern are at lower risk of tdp than the females with female pattern.

Association between HERG K897T polymorphism and QT interval in middle-aged Finnish women

OBJECTIVES

The aim of this study was to test whether a recently reported polymorphism in the HERG gene coding for the rapidly activating delayed rectifier K+ channel has influence on myocardial repolarization.

BACKGROUND

The length of myocardial repolarization, measured as the QT interval, has a hereditary component, but no genes that would explain the variability of repolarization have been identified in healthy subjects.

METHODS

QT intervals were measured from the 12-lead electrocardiogram in a random middle-aged population (226 men/187 women). The longest QT interval at any of the 12 leads (QTmax), QTV(2), and the Tpeak-Tend interval were used as measures of repolarization. Deoxyribonucleic acid samples were genotyped for the nucleotide 2690A>C variation of the HERG gene, corresponding to the HERG K(lysine)897T(threonine) amino acid polymorphism.

RESULTS

The allele frequencies were 0.84 (A) and 0.16 (C). Females with the genotype AC or CC had longer QTcmax (477 +/- 99 ms) and Tpeak-Tend intervals (143 +/- 95 ms) than females with the genotype AA (441 +/- 69 ms and 116 +/- 65 ms, p = 0.005 and p = 0.025, respectively). In males, the QTcmax and the Tpeak-Tend intervals did not differ between the genotypes. After adjustment for echocardiographic and various laboratory variables, the HERG K897T polymorphism remained as an independent predictor of QTcmax (p = 0.009) and the Tpeak-Tend intervals (p = 0.026) in females. CONCLUSIONS; The common K897T polymorphism of the HERG channel is associated with the maximal duration and transmural dispersion of ventricular repolarization in middle-aged females.

Familial aggregation of QT-interval variability in a general population: results from the NHLBI Family Heart Study

QT-interval prolongation is associated with increased risk of cardiac death. Although information on genetics and molecular mechanisms of the congenital long QT syndrome is mounting, limited data are available on the genetics of QT interval in the general population. Heart rate adjusted QT intervals (Bazett's QTc, and QT index (QTI)) were assessed by electrocardiography in 2399 members aged 25-91 years of 468 randomly selected families participating in the NHLBI Family Heart Study. Familial correlation and segregation analyses were performed to evaluate the genetics of the variability of QT interval in this population. The parent-offspring (0.14+/-0.03) and sibling (0.18+/-0.03) correlations for age and sex-adjusted QTc were moderate, while the spouse correlation was close to zero (0.09+/-0.06). This suggests that there are familial/genetic influences on QT-interval variability. Segregation analysis results suggest that there is a major effect in addition to heritable multifactorial effects (h2=0.34), but the major effect did not follow Mendelian inheritance. Further adjustments of QTc for other major cardiovascular risk factors did not significantly change the results. Similar results were found for QTI. The QT-interval variation in the general population is influenced by moderate heritable multifactorial effects in addition to a major effect. A major gene effect is not directly supported.