ExomeChip-Wide Analysis of 95 626 Individuals Identifies 10 Novel Loci Associated With QT and JT Intervals

BACKGROUND

QT interval, measured through a standard ECG, captures the time it takes for the cardiac ventricles to depolarize and repolarize. JT interval is the component of the QT interval that reflects ventricular repolarization alone. Prolonged QT interval has been linked to higher risk of sudden cardiac arrest.

METHODS AND RESULTS

We performed an ExomeChip-wide analysis for both QT and JT intervals, including 209 449 variants, both common and rare, in 17 341 genes from the Illumina Infinium HumanExome BeadChip. We identified 10 loci that modulate QT and JT interval duration that have not been previously reported in the literature using single-variant statistical models in a meta-analysis of 95 626 individuals from 23 cohorts (comprised 83 884 European ancestry individuals, 9610 blacks, 1382 Hispanics, and 750 Asians). This brings the total number of ventricular repolarization associated loci to 45. In addition, our approach of using coding variants has highlighted the role of 17 specific genes for involvement in ventricular repolarization, 7 of which are in novel loci.

CONCLUSIONS

Our analyses show a role for myocyte internal structure and interconnections in modulating QT interval duration, adding to previous known roles of potassium, sodium, and calcium ion regulation, as well as autonomic control. We anticipate that these discoveries will open new paths to the goal of making novel remedies for the prevention of lethal ventricular arrhythmias and sudden cardiac arrest.

Fine mapping of QT interval regions in global populations refines previously identified QT interval loci and identifies signals unique to African and Hispanic descent populations

BACKGROUND

The electrocardiographically measured QT interval (QT) is heritable and its prolongation is an established risk factor for several cardiovascular diseases. Yet, most QT genetic studies have been performed in European ancestral populations, possibly reducing their global relevance.

OBJECTIVE

To leverage diversity and improve biological insight, we fine mapped 16 of the 35 previously identified QT loci (46%) in populations of African American (n = 12,410) and Hispanic/Latino (n = 14,837) ancestry.

METHODS

Racial/ethnic-specific multiple linear regression analyses adjusted for heart rate and clinical covariates were examined separately and in combination after inverse-variance weighted trans-ethnic meta-analysis.

RESULTS

The 16 fine-mapped QT loci included on the Illumina Metabochip represented 21 independent signals, of which 16 (76%) were significantly (P-value≤9.1×10-5) associated with QT. Through sequential conditional analysis we also identified three trans-ethnic novel SNPs at ATP1B1, SCN5A-SCN10A, and KCNQ1 and three Hispanic/Latino-specific novel SNPs at NOS1AP and SCN5A-SCN10A (two novel SNPs) with evidence of associations with QT independent of previous identified GWAS lead SNPs. Linkage disequilibrium patterns helped to narrow the region likely to contain the functional variants at several loci, including NOS1AP, USP50-TRPM7, and PRKCA, although intervals surrounding SLC35F1-PLN and CNOT1 remained broad in size (>100 kb). Finally, bioinformatics-based functional characterization suggested a regulatory function in cardiac tissues for the majority of independent signals that generalized and the novel SNPs.

CONCLUSION

Our findings suggest that a majority of identified SNPs implicate gene regulatory dysfunction in QT prolongation, that the same loci influence variation in QT across global populations, and that additional, novel, population-specific QT signals exist.

Evidence of heterogeneity by race/ethnicity in genetic determinants of QT interval

BACKGROUND

QT interval (QT) prolongation is an established risk factor for ventricular tachyarrhythmia and sudden cardiac death. Previous genome-wide association studies in populations of the European descent have identified multiple genetic loci that influence QT, but few have examined these loci in ethnically diverse populations.

METHODS

Here, we examine the direction, magnitude, and precision of effect sizes for 21 previously reported SNPs from 12 QT loci, in populations of European (n = 16,398), African (n = 5,437), American Indian (n = 5,032), Hispanic (n = 1,143), and Asian (n = 932) descent as part of the Population Architecture using Genomics and Epidemiology (PAGE) study. Estimates obtained from linear regression models stratified by race/ethnicity were combined using inverse-variance weighted meta-analysis. Heterogeneity was evaluated using Cochran's Q test.

RESULTS

Of 21 SNPs, 7 showed consistent direction of effect across all 5 populations, and an additional 9 had estimated effects that were consistent across 4 populations. Despite consistent direction of effect, 9 of 16 SNPs had evidence (P < 0.05) of heterogeneity by race/ethnicity. For these 9 SNPs, linkage disequilibrium plots often indicated substantial variation in linkage disequilibrium patterns among the various racial/ethnic groups, as well as possible allelic heterogeneity.

CONCLUSIONS

These results emphasize the importance of analyzing racial/ethnic groups separately in genetic studies. Furthermore, they underscore the possible utility of trans-ethnic studies to pinpoint underlying casual variants influencing heritable traits such as QT.

Racial susceptibility for QT prolongation in acute drug overdoses

BACKGROUND AND PURPOSE

QT prolongation independently predicts adverse cardiovascular events in suspected poisoning. We aimed to evaluate the association between race and drug-induced QT prolongation for patients with acute overdose.

METHODS

This was a cross-sectional observational study at two urban teaching hospitals. Consecutive adult ED patients with acute drug overdose were prospectively enrolled over a two year period. The primary outcome, long-QT, was defined using standard criteria: QTc>470 ms in females and>460 ms in males. The association between race and drug-induced QT prolongation was tested, considering several confounding variables.

RESULTS

In 472 patients analyzed (46% female, mean age 42.3), QT prolongation occurred in 12.7%. Blacks had two-fold increased odds of drug-induced QT prolongation (OR 2.01, CI 1.03-3.91) and Hispanics had 48% decreased odds of drug-induced QT prolongation (OR 0.52, CI 0.29-0.94).

CONCLUSIONS

We found significant racial susceptibility to drug-induced QT prolongation in this large urban study of acute overdoses.

Sex-steroid hormones and electrocardiographic QT-interval duration: findings from the third National Health and Nutrition Examination Survey and the Multi-Ethnic Study of Atherosclerosis

The association between physiologic levels of sex hormones and QT-interval duration in humans was evaluated using data from 727 men enrolled in the Third National Health and Nutrition Examination Survey and 2,942 men and 1,885 postmenopausal women enrolled in the Multi-Ethnic Study of Atherosclerosis (MESA). Testosterone, estradiol, and sex hormone-binding globulin levels were measured in serum and free testosterone was calculated from those values. QT interval was measured using a standard 12-lead electrocardiogram. In men from the Third National Health and Nutrition Survey, the multivariate adjusted differences in average QT-interval duration comparing the highest quartiles with the lowest quartiles of total testosterone and free testosterone were -8.5 ms (95% confidence interval (CI): -15.5, -1.4) and -8.0 ms (95% CI: -13.2, -2.8), respectively. The corresponding differences were -1.8 ms (95% CI: -3.8, -0.2), and -4.7 ms (95% CI: -6.7, -2.6), respectively, in men from MESA and -0.6 ms (95% CI: -3.0, 1.8) and 0.8 ms (95% CI: -1.6, 3.3), respectively, in postmenopausal women from MESA. Estradiol levels were not associated with QT-interval duration in men, but there was a marginally significant positive association in postmenopausal women. The findings suggest that testosterone levels may explain differences in QT-interval duration between men and women and could be a contributor to population variability in QT-interval duration among men.

Invited commentary: sex-steroid hormones and QT-interval duration

In this issue of the Journal, Zhang et al. (Am J Epidemiol. 2011;174(4):403-411) make a substantial contribution to research in the area of hormonal influences on cardiac repolarization by demonstrating an inverse association between testosterone levels and the Bazett's adjusted QT interval (QTc) and RR-adjusted QT interval in men but not in postmenopausal women. They suggest that testosterone levels might explain the difference in QTc-interval duration between men and women and could contribute to population variability in QTc-interval duration among men. In this commentary, the gender difference and the role of testosterone in human cardiac repolarization are addressed. In addition, the gender differences in the congenital long-QT syndrome, drug-induced ventricular arrhythmias, and sudden cardiac death are discussed.

Genetic testing for long-QT syndrome: distinguishing pathogenic mutations from benign variants

BACKGROUND

Genetic testing for long-QT syndrome (LQTS) has diagnostic, prognostic, and therapeutic implications. Hundreds of causative mutations in 12 known LQTS-susceptibility genes have been identified. Genetic testing that includes the 3 most commonly mutated genes is available clinically. Distinguishing pathogenic mutations from innocuous rare variants is critical to the interpretation of test results. We sought to quantify the value of mutation type and gene/protein region in determining the probability of pathogenicity for mutations.

METHODS AND RESULTS

Type, frequency, and location of mutations across KCNQ1 (LQT1), KCNH2 (LQT2), and SCN5A (LQT3) were compared between 388 unrelated "definite" (clinical diagnostic score >or=4 and/or QTc >or=480 ms) cases of LQTS and >1300 healthy controls for each gene. From these data, estimated predictive values (percent of mutations found in definite cases that would cause LQTS) were determined according to mutation type and location. Mutations were 10 times more common in cases than controls (0.58 per case versus 0.06 per control). Missense mutations were the most common, accounting for 78%, 67%, and 89% of mutations in KCNQ1, KCNH2, and SCN5A in cases and >95% in controls. Nonmissense mutations have an estimated predictive value >99% regardless of location. In contrast, location appears to be critical for characterizing missense mutations. Relative frequency of missense mutations between cases and controls ranged from approximately 1:1 in the SCN5A interdomain linker to infinity in the pore, transmembrane, and linker in KCNH2. These correspond to estimated predictive values ranging from 0% in the interdomain linker of SCN5A to 100% in the transmembrane/linker/pore regions of KCNH2. The estimated predictive value is also high in the linker, pore, transmembrane, and C terminus of KCNQ1 and the transmembrane/linker of SCN5A.

CONCLUSIONS

Distinguishing pathogenic mutations from rare variants is of critical importance in the interpretation of genetic testing in LQTS. Mutation type, mutation location, and ethnic-specific

BACKGROUND

should be viewed as variants of uncertain significance and prompt further investigation to clarify the likelihood of disease causation. However, mutations in regions such as the transmembrane, linker, and pore of KCNQ1 and KCNH2 may be defined confidently as high-probability LQTS-causing mutations. These findings will have implications for other genetic disorders involving mutational analysis.

The C-allele of tissue inhibitor of metalloproteinases 2 is associated with increased magnitude of QT dispersion prolongation in elderly Chinese - 4-year follow-up study

BACKGROUND

Matrix metalloproteinases (MMP) and tissue inhibitor of metalloproteinases (TIMP) trigger the signal cascade instigating cardiac remodeling and fibrosis, which lead to changes of repolarization variables. We investigate the influence of MMP9-1562 C/T and TIMP2-418 G/C gene polymorphisms on repolarization parameters including QT dispersion (QTd) and the peak and the end of the T wave interval (Tpe) in a prospective cohort.

METHODS

Of 1500 people screened, 106 elderly Chinese without organic heart disease were recruited and received electrocardiography at the baseline, second and 4th year follow-ups. The QTc (corrected QT), QTd, QTc dispersion (QTcd) and Tpe were manually calculated.

RESULTS

Age was 72.7+/-4.1 y (range 62-81 y). QTd, QTcd and Tpe were significantly prolonged (all p <0.001 at the 2nd and 4th year). At the 4th year the magnitude of QTd prolongation but not Tpe was significantly higher in subjects carrying the TIMP2 C-allele than non C-allele carriers (p=0.033) as well as QTcd (p=0.010). This association was still significant in multivariate analyses (p=0.012 and p=0.003 for QTd and QTcd, respectively) but not in MMP9 genotype.

CONCLUSIONS

The elderly Chinese with TIMP2 C-allele have higher magnitude of QTd and QTcd prolongation.

Defining the Cellular Phenotype of “Ankyrin-B Syndrome” Variants

Background— Mutations in the ankyrin-B gene ( ANK2 ) cause type 4 long-QT syndrome and have been described in kindreds with other arrhythmias. The frequency of ANK2 variants in large populations and molecular mechanisms underlying the variability in the clinical phenotypes are not established. More importantly, there is no cellular explanation for the range of severity of cardiac phenotypes associated with specific ANK2 variants.

Methods and Results— We performed a comprehensive screen of ANK2 in populations (control, congenital arrhythmia, drug-induced long-QT syndrome) of different ethnicities to discover unidentified ANK2 variants. We identified 7 novel nonsynonymous ANK2 variants; 4 displayed abnormal activity in cardiomyocytes. Including the 4 new variants, 9 human ANK2 loss-of-function variants have been identified. However, the clinical phenotypes associated with these variants vary strikingly, from no obvious phenotype to manifest long-QT syndrome and sudden death, suggesting that mutants confer a spectrum of cellular phenotypes. We then characterized the relative severity of loss-of-function properties of all 9 nonsynonymous ANK2 variants identified to date in primary cardiomyocytes and identified a range of in vitro phenotypes, including wild-type, simple loss-of-function, and severe loss-of-function activity, seen with the variants causing severe human phenotypes.

Conclusions— We present the first description of differences in cellular phenotypes conferred by specific ANK2 variants. We propose that the various degrees of ankyrin-B loss of function contribute to the range of severity of cardiac dysfunction. These data identify ANK2 variants as modulators of human arrhythmias, provide the first insight into the clinical spectrum of “ankyrin-B syndrome,” and reinforce the role of ankyrin-B–dependent protein interactions in regulating cardiac electrogenesis.

D-Allele of ACE Polymorphism is Associated With Increased Magnitude of QT Dispersion Prolongation in Elderly Chinese 4-Year Follow-up Study

BACKGROUND

There has not been a longitudinal investigation of the influence of angiotensin-converting enzyme (ACE) insertion/deletion and angiotensinogen (AGT) M235T gene polymorphisms on repolarization parameters, such as QT dispersion (QTd) and the peak and the end of the T-wave interval (Tpe).

METHODS AND RESULTS

Electrocardiographys were recorded from 106 elderly Chinese at baseline, and 2nd and 4th year follow-up. The corrected QT (QTc), QTd, QTc dispersion (QTcd) and Tpe were manually calculated. Average age was 72.7+/-4.1 years (range 62-81). QTd, QTcd and Tpe were significantly prolonged (all p<0.001 at the 2nd and 4th year). At the 4th year the magnitude of the QTd prolongation, but not Tpe, was significantly higher in subjects carrying the ACE D allele than non-D-allele carriers (p=0.001), as was QTcd (p=0.002). This association was still significant in the multivariate analyses (p<0.001 and p=0.001 for QTc and QTcd, respectively). No significant correlation was found between repolarization parameters and AGT genotype.

CONCLUSIONS

This longitudinal study shows that the ageing process is associated with prolongation of QTd, QTcd and Tpe after 4 years follow-up. The elderly Chinese subjects with the ACE D-allele had greater prolongation QTd and QTcd.

Possible interethnic differences in quinidine-induced QT prolongation between healthy Caucasian and Korean subjects

AIMS

The aim of this study was to evaluate the pharmacokinetics and pharmacodynamics of quinidine-induced QT prolongation in healthy Caucasian and Korean subjects to investigate interethnic differences in susceptibility to drug-induced arrhythmia.

METHODS

A randomized, double-blind crossover study was conducted in 24 (12 male and 12 female) Korean and 13 (seven male and six female) Caucasian subjects. After a 20 min infusion of quinidine (4 mg kg(-1)) or saline, the serum concentration of quinidine and the QT interval corrected by Bazett's formula (QTc) were monitored. The dynamic data were analyzed by means of a population modelling approach using NONMEM.

RESULTS

There were no statistical differences in the pharmacokinetic profiles of quinidine between ethnic groups. The QTc values in Caucasians were higher than those in Koreans at the same quinidine concentrations, especially at higher quinidine concentrations and in female subjects. According to an E(max) model [equation: see text], the population modelling approach revealed that E0 (ms) was related to gender (408 + [34*(1 - Sex)]; 1 for male and 0 for female), DeltaE(max) (ms) was related to ethnicity ((136*f(ETHN)) + C(female): f(ETHN) = 1 for Koreans and 1.26 for Caucasians; C(female) was 106 only for Caucasian females), and EC50 was estimated to be 3.13 microm.

CONCLUSIONS

These results suggest that Korean subjects were less sensitive to quinidine-induced QT prolongation than Caucasian subjects, and that this trend was particularly true for females. Further population-based studies are merited to characterize more completely the ethnic differences in drug-induced QT prolongation between Asians and other ethnic groups.

The long QT syndrome: therapeutic implications of a genetic diagnosis

The congenital long QT syndrome (LQTS) is a hereditary disorder characterized by a prolonged QT interval and a polymorphic ventricular tachycardia, known as torsade de pointes (TdP), leading to severe cardiac events such as syncope and/or sudden cardiac death. Molecular genetic studies have revealed a total of eight forms of congenital LQTS caused by mutations in genes of the potassium, sodium and calcium channels or membrane adapter located on chromosomes 3, 4, 7, 11, 12, 17 and 21. Genotype-phenotype correlation in clinical and experimental studies has been investigated in detail in the LQT1, LQT2 and LQT3 syndromes which constitute more than 90% of genotyped patients with LQTS, enabling us to stratify risk and to effectively treat genotyped patients.

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.

Characterization of a KCNQ1/KVLQT1 polymorphism in Asian families with LQT2: implications for genetic testing

Congenital long QT syndrome (LQTS) is a genetic disease that predisposes affected individuals to arrhythmias, syncope, and sudden death. Mutations in several ion channel genes have been discovered in different families with LQTS: KCNQ1 (KVLQT1, LQT1), KCNH2 (HERG, LQT2), SCN5A (LQT3), KCNE1 (minK, LQT5), and KCNE2 (MiRP1, LQT6). Previously, the P448R-KVLQT1 missense mutation has been reported as an LQT1-causing mutation. In this report, we demonstrate the presence of the P448R polymorphism in two, unrelated Chinese LQTS families. Although absent from 500 reference alleles derived from 150 white and 100 African-American subjects, P448R was present in 14% of healthy Chinese volunteers. Given the inconsistencies between the genotype (LQT1) and clinical phenotype (LQT2) in our two LQTS families, together with the finding that the P448R appears to be a common, ethnic-specific polymorphism, mutational analysis was extended to the other LQTS-causing genes resulting in the identification of distinct HERG missense mutations in each of these two families. Heterologous expression of P448R-KVLQT1 yielded normal, wild-type (WT) currents. In contrast, the two unique HERG mutations resulted in dominant-negative suppression of the WT HERG channel. Our study has profound implications for those engaged in genetic research. Importantly, one child of the original proband was initially diagnosed with LQT1 based upon the presence of P448R-KVLQT1 and was treated with beta-blockers. However, he did not possess the subsequently determined LQT2-causing mutation. On the other hand, his untreated P448R-negative brother harbored the true, disease-causing HERG mutation. These findings underscore the importance of distinguishing channel polymorphisms from mutations pathogenic for LQTS and emphasize the importance of using appropriate ethnically matched controls in the genotypic analysis of LQTS.

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.

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

QT interval prolongation not attributed to long QT syndromes is reported to be associated with increased risk of sudden and nonsudden cardiac death. Genetic and environmental determinants of QTc interval were investigated in an unselected free living population sample of 80 kindreds residing in kibbutz settlements in Israel. The sample included 214 males and 227 females aged 15-97 years. There was a significant familial aggregation of adjusted QT interval levels, as indicated by inter- and intraclass correlation coefficients significantly different from zero. Complex segregation analysis applied to the sex- and age-adjusted data was not conclusive and heterogeneous etiologies for individual differences were suggested. There was evidence for a single recessive locus (q = 0.173) with a major effect in addition to polygenic effects (h2 = 0.41) that explained the mixture of distributions. In parallel, a nontransmitted environmental major factor in addition to polygenic effects that explained the adjusted variation in QTc could not be rejected. Similar results were obtained upon the adjustment for sex, age, and environmental covariables. The major factor, either genetic or environmental, and polygenic-loci accounted for about 20 and 33% of the adjusted QTc variation, respectively. Furthermore, sex, age, measured environmental covariables, the unmeasured major factor, and the unmeasured polygenes could account for 63% of the variation of QTc in these families. Our data provide evidence for a major factor, either genetic or environmental, in addition to a polygenic background, influencing QT interval levels in a population-based sample of pedigrees.

Homozygous deletion in KVLQT1 associated with Jervell and Lange-Nielsen syndrome

BACKGROUND

Long-QT (LQT) syndrome is a cardiac disorder that causes syncope, seizures, and sudden death from ventricular arrhythmias, specifically torsade de pointes. Both autosomal dominant LQT (Romano-Ward syndrome) and autosomal recessive LQT (Jervell and Lange-Nielsen syndrome, JLNS) have been reported. Heterozygous mutations in 3 potassium channel genes, KVLQT1, KCNE1 (minK), and HERG, and the cardiac sodium channel gene SCN5A cause autosomal dominant LQT. Autosomal recessive LQT, which is associated with deafness, has been found to occur with homozygous mutations in KVLQT1 and KCNE1 in JLNS families in which QTc prolongation was inherited as a dominant trait.

METHODS AND RESULTS

An Amish family with clinical evidence of JLNS was analyzed for mutations by use of single-strand conformation polymorphism and DNA sequencing analyses for mutations in all known LQT genes. A novel homozygous 2-bp deletion in the S2 transmembrane segment of KVLQT1 was identified in affected members of this Amish family in which both QTc prolongation and deafness were inherited as recessive traits. This deletion represents a new JLNS-associated mutation in KVLQT1 and has deleterious effects on the KVLQT1 potassium channel, causing a frameshift and the truncation of the KVLQT1 protein. In contrast to previous reports in which LQT was inherited as a clear dominant trait, 2 parents in the JLNS family described here have normal QTc intervals (0.43 and 0.44 seconds, respectively).

CONCLUSIONS

A novel homozygous KVLQT1 mutation causes JLNS in an Amish family with deafness that is inherited as an autosomal recessive trait.

Analysis of HLA and disease susceptibility: chromosome 6 genes and sex influence long-QT phenotype

The long-QT (LQT) syndrome is a genetically complex disorder that is characterized by syncope and fatal ventricular arrhythmias. LQT syndrome, as defined by a prolonged electrocardiographic QT interval, has a higher incidence in females than in males and does not exhibit Mendelian transmission patterns in all families. Among those families that are nearly consistent with Mendelian transmission, linkage between a locus for LQT syndrome and the H-ras-1 locus on the short arm of chromosome 11 has been reported in some families but not in others. Earlier analyses suggesting that LQT syndrome might be caused by a gene in the HLA region of chromosome 6 were not confirmed by standard linkage analyses. Here, we present an analysis of HLA haplotype sharing among affected pedigree members, showing an excess of haplotype sharing in a previously published Japanese pedigree and possibly also in 15 families of European descent. The haplotypes shared by affected individuals derive from both affected and unaffected parents. In an analysis of independent (unrelated) HLA haplotypes, we also found a nonrandom distribution of HLA-DR genes in LQT syndrome patients compared with controls, suggesting an association between the LQT phenotype and specific HLA-DR genes. Our data indicate that DR2 has a protective effect and, particularly in males, that DR7 may increase susceptibility to the LQT syndrome. Thus, LQT syndrome may be influenced by genes on chromosomes 11 and 6, possibly with a sex-specific effect. These results provide a model for an effect of HLA-region genes inherited from either parent on the expression of an illness that may be determined principally by alleles at loci not linked to HLA.

Prolonged QT interval and risk of sudden death in South-East Asian men

Sudden death in sleep occurs in substantial numbers among young men in South-East Asia. The frequencies of electrocardiographic abnormalities were measured in groups with varying risks of such sudden death. The mean heart-rate-corrected QT interval (QTc) was significantly (p less than 0.05) greater among 123 Laotian refugees in Thailand at high risk (405 [95% confidence interval 397-413] ms) than in 77 Laotian refugees in the United States at lower risk (364 [359-369] ms) and 199 non-Asian US residents at negligible risk (358 [354-362] ms). Among refugees in Thailand, prolonged QTc interval was associated with poor thiamine status and a history of seizure-like episodes in sleep. Thiamine deficiency may be a cause of prolonged QT interval and sudden death in this region.