David Curb

A Polymorphism in the β1 Adrenergic Receptor Is Associated with Resting Heart Rate

Resting heart rate is significantly associated with cardiovascular morbidity and mortality. However, the extent to which resting heart rate is genetically determined is poorly understood, and no genes have been found that contribute to variation in resting heart rate. Because signaling through the beta1 adrenergic receptor is a key determinant of cardiac function, we tested whether polymorphisms in this receptor are associated with resting heart rate. A cohort of >1,000 individuals of Chinese and Japanese descent, from nuclear families, was genotyped for two polymorphisms, resulting in a serine/glycine substitution at amino acid 49 (Ser49Gly) and an arginine/glycine substitution at residue 389 (Arg389Gly), in the beta1 adrenergic receptor. For comparison, polymorphisms in the beta2 and beta3 adrenergic receptors were also evaluated. The Ser49Gly polymorphism was significantly associated (P=.0004) with resting heart rate, independent of other variables, such as body-mass index, age, sex, ethnicity, exercise, smoking, alcohol intake, hypertension status, and treatment with beta blockers. The data support an additive model in which individuals heterozygous for the Ser49Gly polymorphism had mean heart rates intermediate to those of either type of homozygote, with Ser homozygotes having the highest mean heart rate and with Gly homozygotes having the lowest. Neither the Arg389Gly polymorphism in the beta1 adrenergic receptor nor polymorphisms in the beta2 and beta3 adrenergic receptors were associated with resting heart rate. The heritability of heart rate was 39.7% +/- 7.1% (P<10-7).

A Combined Analysis of Genomewide Linkage Scans for Body Mass Index, from the National Heart, Lung, and Blood Institute Family Blood Pressure Program

A combined analysis of genome scans for obesity was undertaken using the interim results from the National Heart, Lung, and Blood Institute Family Blood Pressure Program. In this research project, four multicenter networks of investigators conducted eight individual studies. Data were available on 6,849 individuals from four ethnic groups (white, black, Mexican American, and Asian). The sample represents the largest single collection of genomewide scan data that has been analyzed for obesity and provides a test of the reproducibility of linkage analysis for a complex phenotype. Body mass index (BMI) was used as the measure of adiposity. Genomewide linkage analyses were first performed separately in each of the eight ethnic groups in the four networks, through use of the variance-component method. Only one region in the analyses of the individual studies showed significant linkage with BMI: 3q22.1 (LOD 3.45, for the GENOA network black sample). Six additional regions were found with an associated LOD >2, including 3p24.1, 7p15.2, 7q22.3, 14q24.3, 16q12.2, and 17p11.2. Among these findings, the linkage at 7p15.2, 7q22.3, and 17p11.2 has been reported elsewhere. A modified Fishers omnibus procedure was then used to combine the P values from each of the eight genome scans. A complimentary approach to the meta-analysis was undertaken, combining the average allele-sharing identity by descent (pi) for whites, blacks, and Mexican Americans. Using this approach, we found strong linkage evidence for a quantitative-trait locus at 3q27 (marker D3S2427; LOD 3.40, P=.03). The same location has been shown to be linked with obesity-related traits and diabetes in at least two other studies. These results (1) confirm the previously reported obesity-susceptibility locus on chromosomes 3, 7, and 17 and (2) demonstrate that combining samples from different studies can increase the power to detect common genes with a small-to-moderate effect, so long as the same gene has an effect in all samples considered.

Hypertension in pregnancy as a risk factor for cardiovascular disease later in life

Objective The association between hypertension in pregnancy and future cardiovascular disease (CVD) increasingly is recognized. We aimed to assess the role of hypertension in pregnancy as an independent risk factor for hypertension, coronary heart disease (CHD), and stroke later in life. Methods Women who participated in the Phase 2 (2000–2004) Family Blood Pressure Program study (n = 4782) were categorized into women with no history of pregnancy lasting more than 6 months (n = 718), women with no history of hypertension in pregnancy (n = 3421), and women with a history of hypertension in at least one pregnancy (n = 643). We used Kaplan–Meier and Cox proportional hazard models to estimate and contrast the risks of subsequent diagnoses of hypertension, CHD, and stroke among the groups. Results Women with a history of hypertension in pregnancy, compared with those without such a history, were at increased risks for the subsequent diagnoses of hypertension (50% hypertensive at the age 53 vs. 60, P < 0.001), CHD (14% estimated event rate vs. 11%, P = 0.009), and stroke (12% estimated event rate vs. 5%, P < 0.001). The increased risk for subsequent hypertension remained significant after controlling for race, family history of CVD, smoking, dyslipidemia, and diabetes mellitus, with an adjusted hazard ratio of 1.88 [95% confidence interval (CI) 1.49–2.39, P < 0.001]. After controlling for traditional risk factors, including subsequent hypertension, the increased risk for stroke remained statistically significant (hazard ratio 2.10, 95% CI 1.19–3.71, P = 0.01), but not for CHD. Conclusion Hypertension in pregnancy may be an independent risk factor for subsequent diagnoses of hypertension and stroke.

Combined admixture mapping and association analysis identifies a novel blood pressure genetic locus on 5p13: contributions from the CARe consortium

Admixture mapping based on recently admixed populations is a powerful method to detect disease variants with substantial allele frequency differences in ancestral populations. We performed admixture mapping analysis for systolic blood pressure (SBP) and diastolic blood pressure (DBP), followed by trait-marker association analysis, in 6303 unrelated African-American participants of the Candidate Gene Association Resource (CARe) consortium. We identified five genomic regions (P< 0.001) harboring genetic variants contributing to inter-individual BP variation. In follow-up association analyses, correcting for all tests performed in this study, three loci were significantly associated with SBP and one significantly associated with DBP (P< 10(-5)). Further analyses suggested that six independent single-nucleotide polymorphisms (SNPs) contributed to the phenotypic variation observed in the admixture mapping analysis. These six SNPs were examined for replication in multiple, large, independent studies of African-Americans [Womens Health Initiative (WHI), Maywood, Genetic Epidemiology Network of Arteriopathy (GENOA) and Howard University Family Study (HUFS)] as well as one native African sample (Nigerian study), with a total replication sample size of 11 882. Meta-analysis of the replication set identified a novel variant (rs7726475) on chromosome 5 between the SUB1 and NPR3 genes, as being associated with SBP and DBP (P< 0.0015 for both); in meta-analyses combining the CARe samples with the replication data, we observed P-values of 4.45 × 10(-7) for SBP and 7.52 × 10(-7) for DBP for rs7726475 that were significant after accounting for all the tests performed. Our study highlights that admixture mapping analysis can help identify genetic variants missed by genome-wide association studies because of drastically reduced number of tests in the whole genome.

A Genome Scan for Hypertension Susceptibility Loci in Populations of Chinese and Japanese Origins

BACKGROUND Our understanding of genes that predispose to essential hypertension is poor. METHODS A genome-wide scan for linkage at approximately 10 cM resolution was done on 1425 sibpairs of Chinese and Japanese origins that were concordant for hypertension (N = 661), low-normal blood pressure (BP) (N = 184), or discordant for BP (N = 580). RESULTS There was no significant evidence of linkage to a single locus in the genome. There was suggestive evidence of linkage to chromosome 10p, with a LOD score of 2.5. CONCLUSIONS We can exclude the possibility that a single gene accounts for at least 15% of the variance in hypertension in this population.

Resistin, but Not Adiponectin and Leptin, Is Associated With the Risk of Ischemic Stroke Among Postmenopausal Women Results From the Women's Health Initiative

Background and Purpose— Adipose tissue is considered an endocrine organ that secretes adipokines, which possibly mediate the effects of obesity on the risk of cardiovascular disease. However, there are yet limited prospective data on the association between circulating adipokine levels and the risk of ischemic stroke. We aimed to examine the associations of 3 adipokines (adiponectin, leptin, and resistin) with the risk of ischemic stroke. Methods— We conducted a prospective nested case–control study (972 stroke cases and 972 matched control subjects) within the Womens Health Initiative Observational Study cohort. The control subjects were matched to cases on age, race/ethnicity, date of study enrollment, and follow-up time. Results— Adipokine levels were associated with established stroke risk factors such as obesity and systolic blood pressure. Adjusted for body mass index, the ORs for incident ischemic stroke comparing the highest (Quartile 4) with the lowest quartile (Quartile 1) were 0.81 (95% CI, 0.61 to 1.08; P trend=0.068) for adiponectin, 1.15 (95% CI, 0.83 to 1.59; P trend=0.523) for leptin, and 1.57 (95% CI, 1.18 to 2.08; P trend=0.002) for resistin. The association for resistin remained significant even after accounting for established stroke risk factors (OR, 1.39; 95% CI, 1.01 to 1.90; P trend=0.036). Further adjustment for markers for inflammation, angiogenesis, and endothelial function also did not affect our results. Conclusions— Circulating levels of resistin, but not those of adiponectin or leptin, are associated with an increased risk of incident ischemic stroke in postmenopausal women, independent of obesity and other cardiovascular disease risk factors.

Genetic variation in aldosterone synthase predicts plasma glucose levels.

The mineralocorticoid hormone, aldosterone, is known to play a role in sodium homeostasis. We serendipitously found, however, highly significant association between single-nucleotide polymorphisms in the aldosterone synthase gene and plasma glucose levels in a large population of Chinese and Japanese origin. Two polymorphisms—one in the putative promoter (T-344C) and another resulting in a lysine/arginine substitution at amino acid 173, which are in complete linkage disequilibrium in this population—were associated with fasting plasma glucose levels (P = 0.000017) and those 60 (P = 0.017) and 120 (P = 0.0019) min after an oral glucose challenge. A C/T variant in intron 1, between these polymorphisms, was not associated with glucose levels. Arg-173 and -344C homozygotes were most likely to be diabetic [odds ratio 2.51; 95% confidence interval (C.I.) 1.39–3.92; P = 0.0015] and have impaired fasting glucose levels (odds ratio 3.53; 95% C.I. 2.02–5.5; P = 0.0000036). These results suggest a new role for aldosterone in glucose homeostasis.

Arthritis Increases the Risk for Fractures---Results from the Women’s Health Initiative

Objective. To examine the relationship between arthritis and fracture. Methods. Women were classified into 3 self-reported groups at baseline: no arthritis (n = 83,295), osteoarthritis (OA; n = 63,402), and rheumatoid arthritis (RA; n = 960). Incident fractures were self-reported throughout followup. Age-adjusted fracture rates by arthritis category were generated, and the Cox proportional hazards model was used to test the association between arthritis and fracture. Results. After an average of 7.80 years, 24,137 total fractures were reported including 2559 self-reported clinical spinal fractures and 1698 adjudicated hip fractures. For each fracture type, age-adjusted fracture rates were highest in the RA group and lowest in the nonarthritic group. After adjustment for several covariates, report of arthritis was associated with increased risk for spine, hip, and any clinical fractures. Compared to the nonarthritis group, the risk of sustaining any clinical fracture in the OA group was HR 1.09 (95% CI 1.05, 1.13; p < 0.001) and HR 1.49 (95% CI 1.26, 1.75; p < 0.001) in the RA group. The risk of sustaining a hip fracture was not statistically increased in the OA group (HR 1.11; 95% CI 0.98, 1.25; p = 0.122) compared to the nonarthritis group; however, the risk of hip fracture increased significantly (HR 3.03; 95% CI 2.03, 4.51; p < 0.001) in the RA group compared to the nonarthritis group. Conclusion. The increase in fracture risk confirms the importance of fracture prevention in patients with RA and OA.

Combined analysis of genomewide scans for adult height: results from the NHLBI Family Blood Pressure Program.

A combined analysis of genome scans was performed for adult height in the NHLBI Family Blood Pressure Program. Height data were available on 6752 individuals. Linkage analysis was performed first separately for each of the eight ethnic groups in the four networks using the variance component method. To increase the power to detect the common genetic components affecting height for all the individuals, a linkage analysis was performed subsequently for the combined data set by pooling the average allele-sharing IBD () for all groups. By combining the data, we replicated evidence for a QTL influencing adult height on chromosome 7 (7q31) (LOD=2.46), which has been reported in two previous studies. Suggestive linkage (LOD>1) was found in another six regions in our combined analysis. Evidence for linkage for two of these regions (2p12, 20p11) has also been reported previously.

VASOMOTOR SYMPTOMS AND CORONARY ARTERY CALCIUM IN POSTMENOPAUSAL WOMEN

Objective: We assessed whether vasomotor symptoms (VMS) are associated with coronary artery calcium (CAC) and how hormone therapy (HT) may influence this association. Methods: Participants were a subset of women aged 50 to 59 years with a history of hysterectomy who were enrolled in the Womens Health Initiative (WHI) estrogen-alone clinical trial and underwent a CT scan of the chest at the end of the trial to determine CAC. Participants provided information about VMS (hot flashes and/or night sweats), as well as HT use, on self-administered questionnaires at trial baseline. Results: The sample consisted of 918 women with a mean (SD) age of 55.1 (2.8) years at WHI randomization and 64.8 (2.9) years at CAC ascertainment. The prevalence of a CAC score higher than 0 was 46%, whereas the prevalence of a CAC score of 10 or higher and higher than 100 was 39% and 19%, respectively. At randomization, 77% reported a history of any VMS at any time before or at enrollment in the WHI, whereas 20% reported any VMS present only at enrollment. Compared with those without a history of any VMS and after adjustment for potential confounders, a history of any VMS at any time up to and including WHI enrollment was associated with significantly reduced odds for CAC higher than 0 (odds ratio, 0.66; 95% CI, 0.45-0.98). Moreover, as duration of HT increased, the inverse association between any VMS and CAC moved toward the null. Conclusions: A history of any VMS was significantly associated with reduced odds for CAC independent of traditional cardiovascular disease risk factors and other relevant covariates. This association seems to be influenced by duration of HT.