Major quantitative trait locus for resting heart rate maps to a region on chromosome 4

Differences in heart rate responses to upright posture are associated with variations in the high-frequency power of heart rate variability

High resting heart rate is a cardiovascular risk factor, but limited data exist on the underlying hemodynamics and reproducibility of supine-to-upright increase in heart rate. We recorded noninvasive hemodynamics in 574 volunteers [age, 44.9 yr; body mass index (BMI), 26.4 kg/m2; 49% male] during passive head-up tilt (HUT) using whole body impedance cardiography and radial artery tonometry. Heart rate regulation was evaluated using heart rate variability (HRV) analyses. Comparisons were made between quartiles of supine-to-upright heart rate changes, in which heart rate at rest ranged 62.6-64.8 beats/min (P = 0.285). The average upright increases in heart rate in the quartiles 1-4 were 4.7, 9.9, 13.5, and 21.0 beats/min, respectively (P < 0.0001). No differences were observed in the low-frequency power of HRV, whether in the supine or upright position, or in the high-frequency power of HRV in the supine position. Upright high-frequency power of HRV was highest in quartile 1 with lowest upright heart rate and lowest in quartile 4 with highest upright heart rate. Mean systolic blood pressure before and during HUT (126 vs. 108 mmHg) and the increase in systemic vascular resistance during HUT (650 vs. 173 dyn·s/cm5/m2) were highest in quartile 1 and lowest in quartile 4. The increases in heart rate during HUT on three separate occasions several weeks apart were highly reproducible (r = 0.682) among 215 participants. To conclude, supine-to-upright increase in heart rate is a reproducible phenotype with underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. As heart rate at rest influences prognosis, future research should elucidate the prognostic significance of these phenotypic differences.NEW & NOTEWORTHY Subjects with similar supine heart rates are characterized by variable increases in heart rate during upright posture. Individual heart rate increases in response to upright posture are highly reproducible as hemodynamic phenotypes and present underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. These results indicate that resting heart rate obtained in the supine position alone is not an optimal means of classifying people into groups with differences in cardiovascular function.

Heart rate: an accessible risk indicator in adult congenital heart disease

BACKGROUND

Higher resting heart rate has been described as a risk factor for adverse outcome in healthy individuals and cardiovascular patients. The aim of this study was to evaluate resting heart rate as risk factor in adult congenital heart disease (ACHD).

METHODS

In this prospective observational cohort study, patients with moderate or complex ACHD were included at routine outpatient visit. Standard 12-lead ECGs were obtained in rest. Heart rate was obtained from the ECG automatically by the Modular ECG Analysis System (MEANS). The primary endpoint was all-cause mortality and the secondary endpoint was a composite of all-cause mortality and heart failure. Survival was derived using the Kaplan-Meier estimator. Subgroups based on heart rate tertiles were compared by the log-rank test. Cox proportional hazards models were adjusted for clinical factors including age, sex and diagnosis (moderate vs complex ACHD).

RESULTS

A total of 556 patients were included (median age 32 years (IQR 24-41), 57.6% male). Mean heart rate was 69±13 bpm. Negative chronotropic medication was used by 74 (13.3%) patients. During a median follow-up of 10.1 (IQR 9.6-10.5) years, 36 patients (6.5%) died and 83 (14.9%) reached the secondary endpoint. Patients with higher heart rates had significantly lower survival and heart failure-free survival. After adjusting for clinical factors, heart rate remained associated with mortality (HR 1.57 per 10 bpm, 95% CI 1.26 to 1.96) and mortality or heart failure (HR 1.33 per 10 bpm, 95% CI 1.13 to 1.57).

CONCLUSION

Higher heart rate is associated with lower survival and heart failure-free survival in ACHD.

Thirty loci identified for heart rate response to exercise and recovery implicate autonomic nervous system

Impaired capacity to increase heart rate (HR) during exercise (ΔHR^ex), and a reduced rate of recovery post-exercise (ΔHR^rec) are associated with higher cardiovascular mortality rates. Currently, the genetic basis of both phenotypes remains to be elucidated. We conduct genome-wide association studies (GWASs) for ΔHR^ex and ΔHR^rec in ~40,000 individuals, followed by replication in ~27,000 independent samples, all from UK Biobank. Six and seven single-nucleotide polymorphisms for ΔHR^ex and ΔHR^rec, respectively, formally replicate. In a full data set GWAS, eight further loci for ΔHR^ex and nine for ΔHR^rec are genome-wide significant (P ≤ 5 × 10⁻⁸). In total, 30 loci are discovered, 8 being common across traits. Processes of neural development and modulation of adrenergic activity by the autonomic nervous system are enriched in these results. Our findings reinforce current understanding of HR response to exercise and recovery and could guide future studies evaluating its contribution to cardiovascular risk prediction.

Genome-wide association studies have identified multiple loci for resting heart rate (HR) but the genetic factors associated with HR increase during and HR recovery after exercise are less well studied. Here, the authors examine both traits in a two-stage GWAS design in up to 67,257 individuals from UK Biobank.

Discovery of novel heart rate-associated loci using the Exome Chip

Resting heart rate is a heritable trait, and an increase in heart rate is associated with increased mortality risk. Genome-wide association study analyses have found loci associated with resting heart rate, at the time of our study these loci explained 0.9% of the variation. This study aims to discover new genetic loci associated with heart rate from Exome Chip meta-analyses.Heart rate was measured from either elecrtrocardiograms or pulse recordings. We meta-analysed heart rate association results from 104 452 European-ancestry individuals from 30 cohorts, genotyped using the Exome Chip. Twenty-four variants were selected for follow-up in an independent dataset (UK Biobank, N = 134 251). Conditional and gene-based testing was undertaken, and variants were investigated with bioinformatics methods.We discovered five novel heart rate loci, and one new independent low-frequency non-synonymous variant in an established heart rate locus (KIAA1755). Lead variants in four of the novel loci are non-synonymous variants in the genes C10orf71, DALDR3, TESK2 and SEC31B. The variant at SEC31B is significantly associated with SEC31B expression in heart and tibial nerve tissue. Further candidate genes were detected from long-range regulatory chromatin interactions in heart tissue (SCD, SLF2 and MAPK8). We observed significant enrichment in DNase I hypersensitive sites in fetal heart and lung. Moreover, enrichment was seen for the first time in human neuronal progenitor cells (derived from embryonic stem cells) and fetal muscle samples by including our novel variants.Our findings advance the knowledge of the genetic architecture of heart rate, and indicate new candidate genes for follow-up functional studies.

The role of rare variants in systolic blood pressure: analysis of ExomeChip data in HyperGEN African Americans

Cardiovascular diseases are among the most significant health problems in the United States today, with their major risk factor, hypertension, disproportionately affecting African Americans (AAs). Although GWAS have identified dozens of common variants associated with blood pressure (BP) and hypertension in European Americans, these variants collectively explain <2.5% of BP variance, and most of the genetic variants remain yet to be identified. Here, we report the results from rare-variant analysis of systolic BP using 94,595 rare and low-frequency variants (minor allele frequency, MAF, <5%) from the Illumina exome array genotyped in 2,045 HyperGEN AAs. In addition to single-variant analysis, 4 gene-level association tests were used for analysis: burden and family-based SKAT tests using MAF cutoffs of 1 and 5%. The gene-based methods often provided lower p values than the single-variant approach. Some consistency was observed across these 4 gene-based analysis options. While neither the gene-based analyses nor the single-variant analysis produced genome-wide significant results, the top signals, which had supporting evidence from multiple gene-based methods, were of borderline significance. Though additional molecular validations are required, 6 of the 16 most promising genes are biologically plausible with physiological connections to BP regulation.

Insight into genetic determinants of resting heart rate

BACKGROUND

Recent studies suggested that resting heart rate (RHR) might be an independent predictor of cardiovascular mortality and morbidity. Nonetheless, the interrelation between RHR and cardiovascular diseases is not clear. In order to resolve this puzzle, the importance of genetic determinants of RHR has been recently suggested, but it needs to be further investigated.

OBJECTIVE

The aim of this study was to estimate the contribution of common genetic variations on RHR using Genome Wide Association Study.

METHODS

We performed a Genome Wide Association Study in an isolated population cohort of 1737 individuals, the Italian Network on Genetic Isolates - Friuli Venezia Giulia (INGI-FVG). Moreover, a haplotype analysis was performed. A regression tree analysis was run to highlight the effect of each haplotype combination on the phenotype.

RESULTS

A significant level of association (p<5 × 10(-8)) was detected for Single Nucleotide Polymorphisms (SNPs) in two genes expressed in the heart: MAML1 and CANX. Founding that the three different variants of the haplotype, which encompass both genes, yielded a phenotypic correlation. Indeed, a haplotype in homozygosity is significantly associated with the lower quartile of RHR (RHR ≤ 58 bpm). Moreover no significant association was found between cardiovascular risk factors and the different haplotype combinations.

CONCLUSION

Mastermind-like 1 and Calnexin were found to be associated with RHR. We demonstrated a relation between a haplotype and the lower quartile of RHR in our populations. Our findings highlight that genetic determinants of RHR may be implicated in determining cardiovascular diseases and could allow a better risk stratification.

Influence of heart rate at rest for predicting the metabolic syndrome in older Chinese adults

The aim of this study was to examine the relationship between seated resting heart rate and the metabolic syndrome (MetS) among older residents of Guangzhou, South China. A total of 30,519 older participants (≥50 years) from the Guangzhou Biobank Cohort Study were stratified into quartiles based on seated resting heart rate. The associations between each quartile and the MetS were assessed using multivariable logistic regression. A total of 6,907 (22.8 %) individuals were diagnosed as having the MetS, which was significantly associated with increasing heart rate quartiles (P < 0.001). Participants in the uppermost quartile (mean resting heart rate 91 ± 8 beats/min) of this cardiovascular proxy had an almost twofold increased adjusted risk (odds ratio (95 % CI) = 1.94 (1.79, 2.11), P < 0.001) for the MetS, as compared to those in the lowest quartile (mean resting heart rate, 63 ± 4 beats/min). Heart rate, which is an inexpensive and simple clinical measure, was independently associated with the MetS in older Chinese adults. We hope these observations will spur further studies to examine the usefulness of resting heart rate as a means of risk stratification in such populations, for which targeted interventions should be implemented.

Common genetic variation near the connexin-43 gene is associated with resting heart rate in African Americans: a genome-wide association study of 13,372 participants

BACKGROUND

Genome-wide association studies have identified several genetic loci associated with variation in resting heart rate in European and Asian populations. No study has evaluated genetic variants associated with heart rate in African Americans.

OBJECTIVE

To identify novel genetic variants associated with resting heart rate in African Americans.

METHODS

Ten cohort studies participating in the Candidate-gene Association Resource and Continental Origins and Genetic Epidemiology Network consortia performed genome-wide genotyping of single nucleotide polymorphisms (SNPs) and imputed 2,954,965 SNPs using HapMap YRI and CEU panels in 13,372 participants of African ancestry. Each study measured the RR interval (ms) from 10-second resting 12-lead electrocardiograms and estimated RR-SNP associations using covariate-adjusted linear regression. Random-effects meta-analysis was used to combine cohort-specific measures of association and identify genome-wide significant loci (P≤2.5×10(-8)).

RESULTS

Fourteen SNPs on chromosome 6q22 exceeded the genome-wide significance threshold. The most significant association was for rs9320841 (+13 ms per minor allele; P = 4.98×10(-15)). This SNP was approximately 350 kb downstream of GJA1, a locus previously identified as harboring SNPs associated with heart rate in Europeans. Adjustment for rs9320841 also attenuated the association between the remaining 13 SNPs in this region and heart rate. In addition, SNPs in MYH6, which have been identified in European genome-wide association study, were associated with similar changes in the resting heart rate as this population of African Americans.

CONCLUSIONS

An intergenic region downstream of GJA1 (the gene encoding connexin 43, the major protein of the human myocardial gap junction) and an intragenic region within MYH6 are associated with variation in resting heart rate in African Americans as well as in populations of European and Asian origin.

Genetic locus on mouse chromosome 7 controls elevated heart rate

Elevated heart rate (HR) is a risk factor for cardiovascular diseases. The goal of the study was to map HR trait in mice using quantitative trait locus (QTL) analysis followed by genome-wide association (GWA) analysis. The first approach provides mapping power and the second increases genome resolution. QTL analyses were performed in a C3HeB×SJL backcross. HR and systolic blood pressure (SBP) were measured by the tail-cuff plethysmography. HR was ∼80 beats/min higher in SJL compared with C3HeB. There was a wide distribution of the HR (536-763 beats/min) in N2 mice. We discovered a highly significant QTL (logarithm of odds = 6.7, P < 0.001) on chromosome 7 (41 cM) for HR in the C3HeB×SJL backcross. In the Hybrid Mouse Diversity Panel (58 strains, n = 5-6/strain) we found that HR (beats/min) ranged from 546 ± 12 in C58/J to 717 ± 7 in MA/MyJ mice. SBP (mmHg) ranged from 99 ± 6 in strain I/LnJ to 151 ± 4 in strain BXA4/PgnJ. GWA analyses were done using the HMDP, which revealed a locus (64.2-65.1 Mb) on chromosome 7 that colocalized with the QTL for elevated HR found in the C3HeB×SJL backcross. The peak association was observed for 17 SNPs that are localized within three GABA(A) receptor genes. In summary, we used a combined genetic approach to fine map a novel elevated HR locus on mouse chromosome 7.

Differential effect of β-blockers for heart rate control in coronary artery disease

BACKGROUND

Resting heart rate is an independent risk factor for cardiovascular disease and is mainly controlled by β-blockers (BBs). BBs are part of the optimal medical treatment for coronary artery disease (CAD), and their benefit correlates with resting heart rate (RHR) reduction.

HYPOTHESIS

RHR is poorly controlled in daily practice among patients with stable cardiovascular disease, and control is only achieved by some BBs.

METHODS

Observational, cross-sectional, and multicenter study of CAD patients recruited nationwide from 20 institutions. Antecedents, risk factors, and treatments were collected. Controlled RHR was considered at <70 bpm.

RESULTS

The mean age of the 2897 patients included was 67.4 years (11.4%), and 75.9% were males. Patients treated with a BB (56.5%) had a lower mean age and comorbidities. The mean RHR was 69.6 bpm (12.6). A significantly lower RHR was observed in patients treated with a BB compared to the rest (67.2 vs 73.0 bpm; P<0.01), and no difference was observed in patients treated with a calciumchannel blocker (CCB). The analysis by individual agents identified that only patients treated with atenolol, bisoprolol, and metoprolol had significantly lower RHR than those not receiving a BB. No differences were observed in mean doses of each agent according to RHR control, except for verapamil. BB treatment was independently associated with RHR control (odds ratio [OR]: 2.42, 95% CI: 2.05-2.87; P<0.01), and no association was found for nondihydropyridine CCBs (OR: 0.99, 95% CI: 0.96-1.02; P = 0.38). Bisoprolol (OR: 1.56, 95% CI: 1.38-1.78; P<0.01), atenolol (OR: 2.01, 95% CI: 1.57-3.49; P<0.01), and metoprolol (OR: 1.29, 95% CI: 1.04-1618; P = 0.04) were independently associated with RHR control.

CONCLUSIONS

RHR is poorly controlled in CAD patients, and although BBs are the most efficient therapy, in daily clinical practice RHR <70 bpm is only independently associated with atenolol, bisoprolol, or metoprolol.

Genome-wide association analysis identifies multiple loci related to resting heart rate

Higher resting heart rate is associated with increased cardiovascular disease and mortality risk. Though heritable factors play a substantial role in population variation, little is known about specific genetic determinants. This knowledge can impact clinical care by identifying novel factors that influence pathologic heart rate states, modulate heart rate through cardiac structure and function or by improving our understanding of the physiology of heart rate regulation. To identify common genetic variants associated with heart rate, we performed a meta-analysis of 15 genome-wide association studies (GWAS), including 38,991 subjects of European ancestry, estimating the association between age-, sex- and body mass-adjusted RR interval (inverse heart rate) and approximately 2.5 million markers. Results with P < 5 × 10(-8) were considered genome-wide significant. We constructed regression models with multiple markers to assess whether results at less stringent thresholds were likely to be truly associated with RR interval. We identified six novel associations with resting heart rate at six loci: 6q22 near GJA1; 14q12 near MYH7; 12p12 near SOX5, c12orf67, BCAT1, LRMP and CASC1; 6q22 near SLC35F1, PLN and c6orf204; 7q22 near SLC12A9 and UfSp1; and 11q12 near FADS1. Associations at 6q22 400 kb away from GJA1, at 14q12 MYH6 and at 1q32 near CD34 identified in previously published GWAS were confirmed. In aggregate, these variants explain approximately 0.7% of RR interval variance. A multivariant regression model including 20 variants with P < 10(-5) increased the explained variance to 1.6%, suggesting that some loci falling short of genome-wide significance are likely truly associated. Future research is warranted to elucidate underlying mechanisms that may impact clinical care.

Bivariate genetic association of KIAA1797 with heart rate in American Indians: the Strong Heart Family Study

Heart rate (HR) has been identified as a risk factor for cardiovascular disease (CVD), yet little is known regarding genetic factors influencing this phenotype. Previous research in American Indians (AIs) from the Strong Heart Family Study (SHFS) identified a significant quantitative trait locus (QTL) for HR on chromosome 9p21. Genetic association on HR was conducted in the SHFS. HR was measured from electrocardiogram (ECG) and echocardiograph (Echo) Doppler recordings. We examined 2248 single-nucleotide polymorphisms (SNPs) on chromosome 9p21 for association using a gene-centric statistical test. We replicated the aforementioned QTL [logarithm of odds (LOD) = 4.83; genome-wide P= 0.0003] on chromosome 9p21 in one SHFS population using joint linkage of ECG and Echo HR. After correcting for effective number of SNPs using a gene-centric test, six SNPs (rs7875153, rs7848524, rs4446809, rs10964759, rs1125488 and rs7853123) remained significant. We applied a novel bivariate association method, which was a joint test of association of a single locus to two traits using a standard additive genetic model. The SNP, rs7875153, provided the strongest evidence for association (P = 7.14 x 10(-6)). This SNP (rs7875153) is rare (minor allele frequency = 0.02) in AIs and is located within intron 9 of the gene KIAA1797. To support this association, we applied lymphocyte RNA expression data from the San Antonio Family Heart Study, a longitudinal study of CVD in Mexican Americans. Expression levels of KIAA1797 were significantly associated (P = 0.012) with HR. These findings in independent populations support that KIAA1797 genetic variation may be associated with HR but elucidation of a functional relationship requires additional study.

Obesity-related dyslipidemia associated with FAAH, independent of insulin response, in multigenerational families of Northern European descent

A more thorough understanding of the genetic architecture underlying obesity-related lipid disorders could someday facilitate cardiometabolic risk reduction through early clinical intervention based upon improved characterization of individual risk. In recent years, there has been tremendous interest in understanding the endocannabinoid system as a novel therapeutic target for the treatment of obesity-related dyslipidemia.

AIMS

N-arachidonylethanolamine activates G-protein-coupled receptors within the endocannabinoid system. Fatty acid amide hydrolase (FAAH) is a primary catabolic regulator of N-acylethanolamines, including arachidonylethanolamine. Genetic variants in FAAH have inconsistently been associated with obesity. It is conceivable that genetic variability in FAAH directly influences lipid homeostasis. The current study characterizes the relationship between FAAH and obesity-related dyslipidemia, in one of the most rigorously-phenotyped obesity study cohorts in the USA.

MATERIALS & METHODS

Members of 261 extended families (pedigrees ranging from 4 to 14 individuals) were genotyped using haplotype tagging SNPs obtained for the FAAH locus, including 5 kb upstream and 5 kb downstream. Each SNP was tested for basic obesity-related phenotypes (BMI, waist and hip circumference, waist:hip ratio, fasting glucose, fasting insulin and fasting lipid levels) in 1644 individuals within these 261 families. Each SNP was also tested for association with insulin responsiveness using data obtained from a frequently sampled intravenous glucose tolerance test in 399 individuals (32 extended families).

RESULTS

A well characterized coding SNP in FAAH (rs324420) was associated with increased BMI, increased triglycerides, and reduced levels of high-density lipoprotein cholesterol. Mean (standard deviation) high-density lipoprotein cholesterol level was 40.5 (14.7) mg/dl for major allele homozygotes, 39.1 (10.4) mg/dl for heterozygotes, and 34.8 (8.1) mg/dl for minor allele homozygotes (p < 0.01, Family-Based Association Test). This SNP was not associated with insulin sensitivity, acute insulin response to intravenous glucose, glucose effectiveness or glucose disposition index.

CONCLUSION

Genetic variability in FAAH is associated with dyslipidemia, independent of insulin response.

Impact of body fat mass extent on cardiac autonomic alterations in women

BACKGROUND

Obesity has been associated with significant abnormalities of the cardiac autonomic regulation. However, the precise impact of increasing body weight on cardiac autonomic function and the metabolic and hormonal contributors to these changes are presently unclear. The aim of our study was to explore in subjects with increasing values of body mass index (BMI) the alterations of cardiac autonomic function and to establish the potential role of various metabolic and hormonal contributors to these alterations.

MATERIALS AND METHODS

We investigated time and frequency domain heart rate variability (HRV) parameters taken from 24-h Holter recordings, and several anthropometric, metabolic and hormonal parameters (plasma glucose, insulin, triglycerides, free fatty acids, leptin and adiponectin) in 68 normoglycaemic and normotensive women (mean age of 40 +/- 3 years), subdivided according to their BMI into 15 normal body weight (controls), 15 overweight, 18 obese and 20 morbidly obese.

RESULTS

Heart rate was increased and HRV was decreased in the morbidly obese group as compared with controls. In overall population, a negative association linked body fat mass (FM) to HRV indices. None of the metabolic and hormonal parameters were significantly related to the HRV indices, after they were adjusted for the body FM.

CONCLUSIONS

Morbidly obese, normoglycaemic and normotensive young women have increased HR and low HRV, indicating an abnormal cardiac autonomic function and representing a risk factor for adverse cardiovascular events. A decrease of HRV parameters is associated with a progressive increase of body FM. Other metabolic and hormonal factors, characterising obesity, do not show an independent influence on these HRV alterations.

Genetic variation in cannabinoid receptor 1 (CNR1) is associated with derangements in lipid homeostasis, independent of body mass index

AIMS

In humans, genetic variation in endocannabinergic signaling has been associated with anthropometric measures of obesity. In randomized trials, pharmacological blockade at the level of the cannabinoid receptor 1 (CNR1) receptor not only facilitates weight reduction, but also improves insulin sensitivity and clinical measures of lipid homeostasis. We therefore tested the hypothesis that genetic variation in CNR1 is associated with common obesity-related metabolic disorders.

MATERIALS & METHODS

A total of six haplotype tagging SNPs were selected for CNR1, using data available within the Human HapMap (Centre d'Etude du Polymorphisme Humain population) these included: two promoter SNPs, three exonic SNPs, and a single SNP within the 3'-untranslated region. These tags were then genotyped in a rigorously phenotyped family-based collection of obese study subjects of Northern European origin.

RESULTS & CONCLUSIONS

A common CNR1 haplotype (H4; prevalence 0.132) is associated with abnormal lipid homeostasis. Additional statistical tests using single tagging SNPs revealed that these associations are partly independent of body mass index.

Genetics of variation in serum uric acid and cardiovascular risk factors in Mexican Americans

BACKGROUND

Elevated serum uric acid is associated with several cardiovascular disease (CVD) risk factors such as hypertension, inflammation, endothelial dysfunction, insulin resistance, dyslipidemia, and obesity. However, the role of uric acid as an independent risk factor for CVD is not yet clear.

OBJECTIVE

The aim of the study was to localize quantitative trait loci regulating variation in serum uric acid and also establish the relationship between serum uric acid and other CVD risk factors in Mexican Americans (n = 848; men = 310, women = 538) participating in the San Antonio Family Heart Study.

METHODS

Quantitative genetic analysis was conducted using variance components decomposition method, implemented in the software program SOLAR.

RESULTS

Mean +/- SD of serum uric acid was 5.35 +/- 1.38 mg/dl. Univariate genetic analysis showed serum uric acid and other CVD risk markers to be significantly heritable (P < 0.005). Bivariate analysis showed significant correlation of serum uric acid with body mass index, waist circumference, waist/hip ratio, total body fat, plasma insulin, serum triglycerides, high-density lipoprotein cholesterol, C-reactive protein, and granulocyte macrophage-colony stimulating factor (P < 0.05). A genome-wide scan for detecting quantitative trait loci regulating serum uric acid variation showed a significant logarithm of odds (LOD) score of 4.72 (empirical LOD score = 4.62; P < 0.00001) on chromosome 3p26. One LOD support interval contains 25 genes, of which an interesting candidate gene is chemokine receptor 2.

SUMMARY

There is a significant genetic component in the variation in serum uric acid and evidence of pleiotropy between serum uric acid and other cardiovascular risk factors.

Heritability and linkage study on heart rates in a Mongolian population

Elevated heart rate has been proposed as an independent risk factor for cardiovascular diseases, but their interrelationships are not well understood. In this study, we performed a genome-wide linkage scan in 1,026 individuals (mean age 30.6 years, 54.5% women) from 73 extended families of Mongolia and determined quantitative trait loci that influence heart rate. The DNA samples were genotyped using deCODE 1,039 microsatellite markers for 3 cM density genome-wide linkage scan. Correlation analysis was carried out to evaluate the correlation of the covariates and the heart rate. T-tests of the heart rate were also performed on sex, smoking and alcohol intake. Consequently, this model was used in a nonparametric genome-wide linkage analysis using variance component model to create a multipoint logarithm of odds (LOD) score and a corresponding P value. In the adjusted model, the heritability of heart rate was estimated as 0.32 (P<.0001) and a maximum multipoint LOD score of 2.03 was observed in 77 cM region at chromosome 18. The second largest LOD score of 1.52 was seen on chromosome 5 at 216 cM. Genes located on the specified locations in chromosomes 5 and 18 may be involved in the regulation of heart rate.

Blood pressure and heart rate QTL in mice of the B6/D2 lineage: sex differences and environmental influences

A quantitative trait locus (QTL) approach was used to define the genetic architecture underlying variation in systolic blood pressure (SBP) and heart rate (HR), measured indirectly on seven occasions by the tail cuff procedure. The tests were conducted in 395 F(2) adult mice (197 males, 198 females) derived from a cross of the C57BL/6J (B6) and DBA/2J (D2) strains and in 22 BXD recombinant-inbred (RI) strains. Interval mapping of F(2) data for the first 5 days of measurement nominated one statistically significant and one suggestive QTL for SBP on chromosomes (Chr) 4 and 14, respectively, and two statistically significant QTL for HR on Chr 1 (which was specific to female mice) and Chr 5. New suggestive QTL emerged for SBP on Chr 3 (female-specific) and 8 and for HR on Chr 11 for measurements recorded several weeks after mice had undergone stressful blood sampling procedures. The two statistically significant HR QTL were confirmed by analyses of BXD RI strain means. Male and female F(2) mice did not differ in SBP or HR but RI strain analyses showed pronounced strain-by-sex interactions and a negative genetic correlation between the two measures in both sexes. Evidence for a role for mitochondrial DNA was found for both HR and SBP. QTL for HR and SBP may differ in males and females and may be sensitive to different environmental contexts.

Common Genetic Variants in ANK2 Modulate QT Interval

Background— Spatial and timely variations in QT interval, even within its normal range, may underlie susceptibility to cardiac arrhythmias and sudden cardiac death. Given its important role in cardiac electrophysiology, we hypothesized that common genetic variation in ankyrin-B gene ( ANK2 ) might modify QT interval length.

Methods and Results— The study population consisted of 1188 participants of the World Health Organizational Multinational Monitoring of Trends and Determinants in Cardiovascular Disease (WHO MONICA) general population survey Cooperative Health Research in the Region of Augsburg (KORA S3). Corrected QT interval was calculated using population specific linear regression formulas. A total of 22 single-nucleotide polymorphisms in the genomic region of ANK2 gene were genotyped using TaqMan technology. In a replication study, 6 single nucleotide polymorphisms were genotyped in 3890 individuals from a second population study (KORA S4). The rare variant of the single-nucleotide polymorphism rs6850768 (allele frequency, 0.28) significantly influenced duration of the QT interval, both in KORA S3 and KORA S4 populations. In homozygotes, the shortening of the QT interval was 3.79 ms (95% CI, 1.48 to 5.58; P =0.001 and P =0.0008 for log-additive and dominant model, respectively) in KORA S3 and 2.94 ms (95% CI, 1.11 to 4.77; P =0.001 and P =0.006 for log-additive and dominant genetic model, respectively) in KORA S4. A common 2-locus haplotype (rs11098171-rs6850768; population frequency, 28%) was associated with a QT interval difference of 2.85 ms (permutation; P =0.006) in KORA S3 and 1.23 ms (permutation; P =0.009) in KORA S4. Reverse transcription–polymerase chain reaction expression analysis of the human ANK2 5′ genomic region in the human left ventricular tissue revealed 2 previously unidentified ANK2 5′ exons in the proximity of the identified variants.

Conclusions— Common genetic variants juxtaposed with novel exons in the distant 5′ genomic region of ANK2 influence the QT interval length in the general population. These findings support the role of ankyrin-B in normal cardiac electric activity.

Dysfunction in ankyrin-B-dependent ion channel and transporter targeting causes human sinus node disease

The identification of nearly a dozen ion channel genes involved in the genesis of human atrial and ventricular arrhythmias has been critical for the diagnosis and treatment of fatal cardiovascular diseases. In contrast, very little is known about the genetic and molecular mechanisms underlying human sinus node dysfunction (SND). Here, we report a genetic and molecular mechanism for human SND. We mapped two families with highly penetrant and severe SND to the human ANK2 (ankyrin-B/AnkB) locus. Mice heterozygous for AnkB phenocopy human SND displayed severe bradycardia and rate variability. AnkB is essential for normal membrane organization of sinoatrial node cell channels and transporters, and AnkB is required for physiological cardiac pacing. Finally, dysfunction in AnkB-based trafficking pathways causes abnormal sinoatrial node (SAN) electrical activity and SND. Together, our findings associate abnormal channel targeting with human SND and highlight the critical role of local membrane organization for sinoatrial node excitability.

Heart Rate and Outcome in Patients with Cardiovascular Disease Undergoing Major Noncardiac Surgery

There is an increasing awareness that an elevated resting heart rate is associated with increased all-cause mortality in the general population and that this may be an independent coronary risk factor. This review was undertaken to determine whether heart rate is predictive of increased mortality and major morbidity in noncardiac surgical patients and whether heart rate manipulation improves perioperative outcome. A search of Medline from 1966 until October 2007 was conducted using the terms “heart rate “, “surgery”, “cardiac “, “morbidity”, “mortality” and “perioperative”. The main findings were that an elevated perioperative heart rate, an absolute increase in heart rate and heart rate lability are independent predictors of both short- and long-term adverse outcomes in patients at cardiovascular risk undergoing major noncardiac surgery. Although prospective nonrandomised and retrospective data suggest heart rate control improves perioperative outcome, there is conflicting evidence from randomised trials that perioperative heart rate control improves outcome. This may be because drug-associated bradycardia influences mortality in the perioperative period. Further studies reporting the absolute heart rate, the absolute change of heart rate and the time period of the observations are needed to identify ‘early warning systems’, which may allow earlier triage and improved outcome. Enthusiasm for this approach must be tempered by the appreciation that a J-shaped relationship probably exists between heart rate and morbidity, particularly following bradycardic therapy. Therefore, any bradycardic manipulation of heart rate in the perioperative period must be accompanied by simultaneous attention to other physiological variables associated with increased morbidity and mortality.

Suggestive linkage of a chromosomal locus on 18p11 to cyclothymic temperament in bipolar disorder families

Attempts to identify bipolar disorder (BP) genes have only enjoyed limited success. One potential cause for this problem is that the traditional categorical BP phenotypes currently used in genetic linkage studies are not the most informative, efficient, or biologically relevant. An alternative to these strict categorical BP phenotypes is quantitative BP phenotypes. By isolating one aspect of a complex trait such as BP into a simple, intermediate, quantitative trait, genes that contribute to the larger complex trait can be more readily identified. Along these lines, we utilized a temperament-based measure (cyclothymic temperament) as a quantitative, intermediate BP phenotype in linkage analyses and hypothesized that this measure might more efficiently detect loci for BP or temperamental traits that predispose to BP. A total of 158 individuals with temperament data from 28 BP families were used in the linkage analyses. All pedigrees had a proband diagnosed with BPI or BPII and at least two other family members with a mood disorder diagnosis. An 8 cM genome scan was performed and analyzed using MERLIN nonparametric multipoint regression linkage for a cyclothymic temperament trait. The highest overall LOD score was on chromosome 18 (LOD = 2.71, P = 0.0002). Other linkage peaks which may indicate potential regions of interest were found on chromosomes 3 and 7. The temperament-based cyclothymic trait yielded a higher peak LOD score and a lower P-value than analyses using traditional, categorical phenotypes in a separate analysis including these same families.

Polymorphisms in multiple genes are associated with resting heart rate in a stepwise allele-dependent manner

OBJECTIVE

The purpose of this study was to use a candidate gene approach to identify common polymorphisms that are associated with resting sinus heart rate in a population without overt cardiovascular disease.

BACKGROUND

Increased resting heart rate is significantly associated with susceptibility to development of myocardial infarction, sudden cardiac death, and overall cardiac mortality.

METHODS

A longitudinal cohort of 1468 individuals (active and retired middle-aged Canadian firefighters) who were enrolled in the Firefighters and Their Endothelium (FATE) study was evaluated. Resting heart rate was recorded from the electrocardiogram (ECG) obtained at enrollment. Candidate genes were selected for their known roles in sinus node automaticity and/or its regulation, and single nucleotide polymorphisms (SNPs) with a minor allele frequency of > or =0.20 were targeted. A total of 53 SNPs in 46 genes were selected and analyzed in a screening sample, and 33 SNPs in 29 genes were evaluated in the full population.

RESULTS

Univariate analysis detected five putative associations between HR and SNPs. As expected, environmental covariates were identified. Three polymorphisms, ADRB1 G389R, SCN5a H558R, and CASQ1 intron 2, remained statistically significant and independent of covariates. Some alleles were associated with higher and some with lower heart rates. A stepwise increase in heart rate was observed that was dependent on the number of tachycardia-associated alleles with progressive increases in mean heart rate from 51 to 66 bpm.

CONCLUSIONS

Common polymorphisms are associated with heart rate in a stepwise allele-dependent manner.

Genetic selection on a behavioural fear trait is associated with changes in heart rate variability in quail

This study investigated whether genetic selection on a divergent behavioural trait of fearfulness (tonic immobility duration) was related to changes in the nervous control of the heart. Quail selected for either long or short tonic immobility (LTI or STI, respectively) duration was compared with an unselected control line (CTI). The autonomic control of the heart was assessed by heart rate variability analysis and pharmacological blockades. Quail were surgically fitted with a telemetric device. Heart rate before injection did not differ between the three lines. The vagal-sympathetic effect (VSE) at rest differed significantly from 1 in CTI and STI quail, suggesting that parasympathetic activity was dominant. In LTI quail, VSE did not differ from 1, suggesting a balance between parasympathetic and sympathetic activities. The intrinsic heart rate reached after the successive injections of propranolol and atropine did not differ between lines and was higher than the heart rate at rest in STI, which was in line with results of VSE at rest. After atropine injection, the sympathetic activity indicated by the low-frequency power was lower in CTI than in the two selected quail. After propranolol injection, the parasympathetic activity indicated by the root of the mean squares of successive differences and the high-frequency power was higher in STI than in CTI and LTI quail. Selection on tonic immobility duration thus appears to be associated with changes in the sympathovagal control of the heart, which may influence behavioural responses to stressful situations.

Characterization of different expression patterns of calsarcin-1 and calsarcin-2 in porcine muscle

Calsarcins comprise a novel family of muscle-specific calcineurin-interacting proteins and play an important role in modulating both the function and substrate specificity of calcineurin in muscle cells. In this study, we cloned and characterized calsarcins from pig muscle. The deduced amino acid sequences of porcine calsarcin-1 (CS-1), calsarcin-2 (CS-2), and calsarcin-3 (CS-3) share the same putative calcineurin and alpha-actinin binding regions. Radiation hybrid mapping data indicate that CS-1 and CS-2 map to q2.1-2.5 of pig chromosome 8 (SSC8) and q2.4 of pig chromosome 14 (SSC14), respectively. The mRNA expressions of both CS-1 and CS-2 are regulated in skeletal muscle similarly during postnatal development but not during prenatal development, indicating differences in function, additionally demonstrated by minute differences in cellular localization within Pig Kidney Epithelial cells (PK15). We provide the first evidence that CS-1 is abundantly expressed in porcine heart and has an expression pattern similar to the human gene. This result suggests that the pig may be a suitable animal model to study the function of calsarcins in human heart disease.

Evidence for a gene influencing heart rate on chromosome 5p13-14 in a meta-analysis of genome-wide scans from the NHLBI Family Blood Pressure Program

BACKGROUND

Elevated resting heart rate has been shown in multiple studies to be a strong predictor of cardiovascular disease. Previous family studies have shown a significant heritable component to heart rate with several groups conducting genomic linkage scans to identify quantitative trait loci.

METHODS

We performed a genome-wide linkage scan to identify quantitative trait loci influencing resting heart rate among 3,282 Caucasians and 3,989 African-Americans in three independent networks comprising the Family Blood Pressure Program (FBPP) using 368 microsatellite markers. Mean heart rate measurements were used in a regression model including covariates for age, body mass index, pack-years, currently drinking alcohol (yes/no), hypertension status and medication usage to create a standardized residual for each gender/ethnic group within each study network. This residual was used in a nonparametric variance component model to generate a LOD score and a corresponding P value for each ethnic group within each study network. P values from each ethnic group and study network were merged using an adjusted Fisher's combining P values method and the resulting P values were converted to LOD scores. The entire analysis was redone after individuals currently taking beta-blocker medication were removed.

RESULTS

We identified significant evidence of linkage (LOD = 4.62) to chromosome 10 near 142.78 cM in the Caucasian group of HyperGEN. Between race and network groups we identified a LOD score of 1.86 on chromosome 5 (between 39.99 and 45.34 cM) in African-Americans in the GENOA network and the same region produced a LOD score of 1.12 among Caucasians within a different network (HyperGEN). Combining all network and race groups we identified a LOD score of 1.92 (P = 0.0013) on chromosome 5p13-14. We assessed heterogeneity for this locus between networks and ethnic groups and found significant evidence for low heterogeneity (P < or = 0.05).

CONCLUSION

We found replication (LOD > 1) between ethnic groups and between study networks with low heterogeneity on chromosome 5p13-14 suggesting that a gene in this region influences resting heart rate.

Targeted mutational analysis of ankyrin-B in 541 consecutive, unrelated patients referred for long QT syndrome genetic testing and 200 healthy subjects

BACKGROUND

Mutations in ANK2-encoded ankyrin-B underlie long QT syndrome type 4 (LQT4) and various other dysrhythmia phenotypes.

OBJECTIVES

The purpose of this study was to determine the prevalence and spectrum of ankyrin-B mutations in a large cohort of unrelated patients referred for LQTS genetic testing and among healthy control subjects.

METHODS

Between August 1997 and July 2004, 541 consecutive, unrelated patients (358 females, average age at diagnosis 24 years, average QTc 482 ms) were referred to Mayo Clinic's Sudden Death Genomics Laboratory for comprehensive mutational analysis of the five cardiac channel genes implicated in LQTS: KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3), KCNE1 (LQT5), and KCNE2 (LQT6). Based on this prior analysis, 269 of 541 cases lacked an identifiable mutation (genotype negative). In this study, targeted mutational analysis of 10 ANK2 exons (36,37,39-46) encoding the critical C-terminal regulatory domain or implicated previously as hosting pathogenic mutations was performed on genomic DNA from 541 patients and 200 control subjects using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing.

RESULTS

Overall, 14 distinct nonsynonymous variants (10 novel) were observed in 9 (3.3%) of 269 genotype-negative LQTS patients, 5 (1.8%) of 272 genotype-positive LQTS cases, 4 (4%) of 100 white controls, and 9 (9%) of 100 black controls. Four variants found in controls (L1622I, T1626N, R1788W, and E1813K) were implicated previously as LQT4-associated mutations and displayed functional perturbations in vitro. All genotype-negative LQTS cases hosting ANK2 variants had been diagnosed as "atypical" or "borderline" cases, most presenting with normal QTc, nonexertional syncope, U waves, and/or sinus bradycardia.

CONCLUSION

Nonsynonymous ankyrin-B variants were detected in nearly 3% of unrelated LQTS patients and nearly 7% of healthy control subjects. Genotype-negative LQTS patients with a single ANK2 variant displayed nonexertional syncope, U waves, sinus bradycardia, and extracardiac findings. Whether the identification of previously reported functionally significant variants residing in 2% of apparently healthy subjects suggests proarrhythmic potential or potential misclassification warrants further scrutiny.