Heritability of central systolic pressure augmentation: a twin study

Genetic and Epigenetic Mechanisms Regulating Blood Pressure and Kidney Dysfunction

The pioneering work of Dr Lewis K. Dahl established a relationship between kidney, salt, and high blood pressure (BP), which led to the major genetic-based experimental model of hypertension. BP, a heritable quantitative trait affected by numerous biological and environmental stimuli, is a major cause of morbidity and mortality worldwide and is considered to be a primary modifiable factor in renal, cardiovascular, and cerebrovascular diseases. Genome-wide association studies have identified monogenic and polygenic variants affecting BP in humans. Single nucleotide polymorphisms identified in genome-wide association studies have quantified the heritability of BP and the effect of genetics on hypertensive phenotype. Changes in the transcriptional program of genes may represent consequential determinants of BP, so understanding the mechanisms of the disease process has become a priority in the field. At the molecular level, the onset of hypertension is associated with reprogramming of gene expression influenced by epigenomics. This review highlights the specific genetic variants, mutations, and epigenetic factors associated with high BP and how these mechanisms affect the regulation of hypertension and kidney dysfunction.

Sex Differences in Vascular Aging and Impact of GPER Deletion

Aging is a nonmodifiable risk factor for cardiovascular disease associated with arterial stiffening and endothelial dysfunction. We hypothesized that sex differences exist in vascular aging processes and would be attenuated by global deletion of the G protein-coupled estrogen receptor. Blood pressure was measured by tail cuff plethysmography, pulse wave velocity (PWV) and echocardiography were assessed with high resolution ultrasound, and small vessel reactivity was measured using wire myography in adult (25 weeks) and middle-aged (57 weeks) male and female mice. Adult female mice displayed lower blood pressure and PWV, but this sex difference was absent in middle-aged mice. Aging significantly increased PWV but not blood pressure in both sexes. Adult female carotids were more distensible than males, but this sex difference was lost during aging. Acetylcholine-induced relaxation was greater in female than male mice at both ages, and only males showed aging-induced changes in cardiac hypertrophy and function. GPER deletion removed the sex difference in PWV as well as ex vivo stiffness in adult mice. The sex difference in blood pressure was absent in KO mice and was associated with endothelial dysfunction in females. These findings indicate that the impact of aging on arterial stiffening and endothelial function is not the same in male and female mice. Moreover, nongenomic estrogen signaling through GPER impacted vascular phenotype differently in male and female mice. Delineating sex differences in vascular changes during healthy aging is an important first step in improving early detection and sex-specific treatments in our aging population.

High blood pressure in children and adolescents: current perspectives and strategies to improve future kidney and cardiovascular health

Hypertension is one of the most common causes of preventable death worldwide. The prevalence of pediatric hypertension has increased significantly in recent decades. The cause of this is likely multifactorial, related to increasing childhood obesity, high dietary sodium intake, sedentary lifestyles, perinatal factors, familial aggregation, socioeconomic factors, and ethnic blood pressure (BP) differences. Pediatric hypertension represents a major public health threat. Uncontrolled pediatric hypertension is associated with subclinical cardiovascular disease and adult-onset hypertension. In children with chronic kidney disease (CKD), hypertension is also a strong risk factor for progression to kidney failure. Despite these risks, current rates of pediatric BP screening, hypertension detection, treatment, and control remain suboptimal. Contributing to these shortcomings are the challenges of accurately measuring pediatric BP, limited access to validated pediatric equipment and hypertension specialists, complex interpretation of pediatric BP measurements, problematic normative BP data, and conflicting society guidelines for pediatric hypertension. To date, limited pediatric hypertension research has been conducted to help address these challenges. However, there are several promising signs in the field of pediatric hypertension. There is greater attention being drawn on the cardiovascular risks of pediatric hypertension, more emphasis on the need for childhood BP screening and management, new public health initiatives being implemented, and increasing research interest and funding. This article summarizes what is currently known about pediatric hypertension, the existing knowledge-practice gaps, and ongoing research aimed at improving future kidney and cardiovascular health.

Associations between PHACTR1 gene polymorphisms and pulse pressure in Chinese Han population

A genome-wide association study (GWAS) in Chinese twins was performed to explore associations between genes and pulse pressure (PP) in 2012, and detected a suggestive association in the phosphatase and actin regulator 1 (PHACTR1) gene on chromosome 6p24.1 (rs1223397, P=1.04e⁻⁰⁷). The purpose of the present study was to investigate associations of PHACTR1 gene polymorphisms with PP in a Chinese population. We recruited 347 subjects with PP ≥ 65 mmHg as cases and 359 subjects with 30 ≤ PP ≤ 45 mmHg as controls. Seven single nucleotide polymorphisms (SNPs) in the PHACTR1 gene were genotyped. Logistic regression was performed to explore associations between SNPs and PP in codominant, additive, dominant, recessive and overdominant models. The Pearson’s χ² test was applied to assess the relationships of haplotypes and PP. The A allele of rs9349379 had a positive effect on high PP. Multivariate logistic regression analysis showed that rs9349379 was significantly related to high PP in codominant [AA vs GG, 2.255 (1.132–4.492)], additive [GG vs GA vs AA, 1.368 (1.049–1.783)] and recessive [AA vs GA + GG, 2.062 (1.051–4.045)] models. The positive association between rs499818 and high PP was significant in codominant [AA vs GG, 3.483 (1.044–11.613)] and recessive [AA vs GG + GA, 3.716 (1.119–12.339)] models. No significant association of haplotypes with PP was detected. There was no significant interaction between six SNPs without strong linkage. In conclusion, the present study presents that rs9349379 and rs499818 in the PHACTR1 gene were significantly associated with PP in Chinese population. Future research should be conducted to confirm them.

The genetic risk for hypertension is lower among the Hungarian Roma population compared to the general population

Estimating the prevalence of cardiovascular diseases (CVDs) and risk factors among the Roma population, the largest minority in Europe, and investigating the role of genetic or environmental/behavioral risk factors in CVD development are important issues in countries where they are significant minority. This study was designed to estimate the genetic susceptibility of the Hungarian Roma (HR) population to essential hypertension (EH) and compare it to that of the general (HG) population. Twenty EH associated SNPs (in AGT, FMO3, MTHFR-NPPB, NPPA, NPPA-AS1, AGTR1, ADD1, NPR3-C5orf23, NOS3, CACNB2, PLCE1, ATP2B1, GNB3, CYP1A1-ULK3, UMOD and GNAS-EDN3) were genotyped using DNA samples obtained from HR (N = 1176) and HG population (N = 1178) subjects assembled by cross-sectional studies. Allele frequencies and genetic risk scores (unweighted and weighted genetic risk scores (GRS and wGRS, respectively) were calculated for the study groups and compared to examine the joint effects of the SNPs. The susceptibility alleles were more frequent in the HG population, and both GRS and wGRS were found to be higher in the HG population than in the HR population (GRS: 18.98 ± 3.05 vs. 18.25 ± 2.97, p<0.001; wGRS: 1.52 [IQR: 0.99–2.00] vs. 1.4 [IQR: 0.93–1.89], p<0.01). Twenty-seven percent of subjects in the HR population were in the bottom fifth (GRS ≤ 16) of the risk allele count compared with 21% of those in the HG population. Thirteen percent of people in the HR group were in the top fifth (GRS ≥ 22) of the GRS compared with 21% of those in the HG population (p<0.001), i.e., the distribution of GRS was found to be left-shifted in the HR population compared to the HG population. The Roma population seems to be genetically less susceptible to EH than the general one. These results support preventive efforts to lower the risk of developing hypertension by encouraging a healthy lifestyle.

The relationship of genetic susceptibilities for psychosis with physiological fluctuation in functional MRI data

Previously, schizophrenia is found to be related to the variability of the functional magnetic resonance imaging (fMRI) signal in the white matter. However, evidence about the relationship between genetic vulnerabilities and physiological fluctuation in the brain is lacking. We investigated whether familial risk for psychosis (FR) and polygenic risk score for schizophrenia (PRS) are linked with physiological fluctuation in fMRI data. We used data from the Oulu Brain and Mind study (n = 140-149, aged 20-24 years) that is a substudy of the Northern Finland Birth Cohort 1986. The participants underwent a resting-state fMRI scan. Coefficient of variation (CV) of blood oxygen level dependent (BOLD) signal (CVBOLD) was used as a proxy of physiological fluctuation in the brain. Familial risk was defined to be present if at least one parent had been diagnosed with psychosis previously. PRS was computed based on the results of the prior GWAS by the Schizophrenia Working Group. FR or PRS were not associated with CVBOLD in cerebrospinal fluid, white matter, or grey matter. The findings did not provide evidence for the previous suggestions that genetic vulnerabilities for schizophrenia become apparent in alterations of the variation of the BOLD signal in the brain.

Loss of reticulocalbin 2 lowers blood pressure and restrains ANG II-induced hypertension in vivo

Hypertension affects over 1 billion people worldwide and increases the risk for heart failure, stroke, and chronic kidney disease. Despite high prevalence and devastating impact, its etiology still remains poorly understood for most hypertensive cases. Rcn2, which encodes reticulocalbin 2, is a candidate gene for atherosclerosis that we have previously reported in mice. Here, we identified Rcn2 as a novel regulator of blood pressure in mice. Rcn2 was abundantly expressed in the endothelium and adventitia of normal arteries and was dramatically upregulated in the medial layer of the artery undergoing structural remodeling. Deletion of Rcn2 lowered basal blood pressure and attenuated ANG II-induced hypertension in C57BL/6 mice. siRNA knockdown of Rcn2 dramatically increased production of the nitric oxide (NO) breakdown products nitrite and nitrate by endothelial cells but not by smooth muscle cells. Isolated carotid arteries from Rcn2-/- mice showed an increased sensitivity to the ACh-induced NO-mediated relaxant response compared with arteries of Rcn2+/+ mice. Analysis of a recent meta-data set showed associations of genetic variants near RCN2 with blood pressure in humans. These data suggest that Rcn2 regulates blood pressure and contributes to hypertension through actions on endothelial NO synthase.

The Effect of Genetically Guided Mathematical Prediction and the Blood Pressure Response to Pharmacotherapy in Hypertension Patients

Purpose:

The purpose of this study was to determine the effectiveness of a simple algorithm to mathematically predict a patients’ response to blood pressure (BP) therapy using functional genes in the 3 major organ systems involved in hypertension.

Methods:

Eighty-six patients with controlled hypertension completed 1 study visit consisting of a buccal swab collection, measurement of office BP, and a medical chart review for BP history. Genes in the analysis included 14 functional alleles in 11 genes. These genotypes were mathematically summed per organ system to determine whether a patient would likely respond to target therapy.

Results:

Patients recommended to and taking a diuretic had significantly higher rates of control (<120/<80) than patients recommended but not taking this drug class (0.2 ± 0.1 and 0.03 ± 0.03, respectively). Furthermore, there was a difference between patients genetically recommended and taking an angiotensin receptor blocker (ARB) vs patients recommended but not taking an ARB for the lowest diastolic blood pressure (DBP) and mean arterial pressure (MAP) recorded in the past 2 years (DBP = 66.2 ± 2.9 and 75.3 ± 1.7, MAP = 82.3 ± 2.8 and 89.3 ± 1.5, respectively). In addition, there was a nonsignificant trend for greater reductions in ΔSBP, ΔDBP, and ΔMAP in patients on recommended drug class for beta-blockers, diuretics, and angiotensin II receptor blockers vs patients not on these classes.

Conclusion:

The present study suggests that simple mathematical weighting of functional genotypes known to control BP may be ineffective in predicting control. This study demonstrates the need for a more complex, weighted, multigene algorithm to more accurately predict BP therapy response.

Relationship between a Weighted Multi-Gene Algorithm and Blood Pressure Control in Hypertension

Hypertension (HTN) is a complex disease with interactions among multiple organ systems, including the heart, vasculature, and kidney with a strong heritable component. Despite the multifactorial nature of HTN, no clinical guidelines utilize a multi-gene approach to guide blood pressure (BP) therapy. Non-smokers with a family history of HTN were included in the analysis (n = 384; age = 61.0 ± 0.9, 11% non-white). A total of 17 functional genotypes were weighted according to the previous effect size in the literature and entered into an algorithm. Pharmacotherapy was ranked from 1–4 as most to least likely to respond based on the algorithmic assessment of individual patient’s genotypes. Three-years of data were assessed at six-month intervals for BP and medication history. There was no difference in BP at diagnosis between groups matching the top drug recommendation using the multi-gene weighted algorithm (n = 92) vs. those who did not match (n = 292). However, from diagnosis to nadir, patients who matched the primary recommendation had a significantly greater drop in BP when compared to patients who did not. Further, the difference between diagnosis to current 1-year average BP was lower in the group that matched the top recommendation. These data suggest an association between a weighted multi-gene algorithm on the BP response to pharmacotherapy.

Retinal micro-vascular and aortic macro-vascular changes in postmenopausal women with primary hyperparathyroidism

Aim of the study was to evaluate the micro and macro-vascular changes in patients with primary hyperparathyroidism (PHPT) compared to controls. 30 postmenopausal PHPT women (15 hypertensive and 15 normotensive) and 30 normotensive controls underwent biochemical evaluation of mineral metabolism and measurements of arterial stiffness by 24 hour ambulatory blood pressure monitoring. Retinal microcirculation was imaged by a Retinal Vessel Analyzer. PHPT patients also underwent bone mineral density measurements and kidney ultrasound. PHPT patients had higher mean calcium and parathyroid hormone values compared to controls. Evaluating macro-vascular compartment, we found higher values of 24 hours-systolic, diastolic blood pressure, aortic pulse wave velocity (aPWV) and aortic augmentation index (Aix) in hypertensive PHPT, but not in normotensive PHPT compared to controls. The eye examination showed narrowing arterial and venular diameters of retinal vessels in both hypertensive and normotensive PHPT compared to controls. In hypertensive PHPT, 24 hours systolic blood pressure was associated only with parathyroid hormone (PTH) levels (beta = 0.36, p = 0.04). aPWV was associated with retinal diameter (beta = -0.69, p = 0.003), but not with PTH. Retinal artery diameter was associated with PTH (beta = -0.6, p = 0.008). In the normotensive PHPT, only PTH was associated with retinal artery diameter (beta = -0.60, p = 0.01) and aortic AIx (beta = 0.65, p = 0.02). In conclusion, we found macro-vascular impairment in PHPT and that micro-vascular impairment is negatively associated with PTH, regardless of hypertension in PHPT.

Genetic and environmental determinants of longitudinal stability of arterial stiffness and wave reflection: a twin study

BACKGROUND

We aimed at evaluating the impact of genetic and environmental factors on longitudinal changes in aortic pulse wave velocity (aPWV) and aortic augmentation index (aAIx).

METHOD

Three hundred and sixty-eight Italian and Hungarian adult twins (214 monozygotic, 154 dizygotic) underwent repeated evaluations of aPWV and aAIx (TensioMed Arteriograph). Within-individual/cross-wave, cross-twin/within-wave and cross-twin/cross-wave correlations were calculated; bivariate Cholesky models were fitted to calculate additive genetic (A), shared environmental (C) and unique environmental (E) components.

RESULTS

For both aPWV and aAIx, cross-twin correlations in monozygotic pairs (r between 0.35 and 0.56) were all significant and always higher than in dizygotic pairs, both at wave 1 and at wave 2. Heritability and unshared environmental proportion of variance at each wave were substantially time-invariant for aPWV (heritability 0.51, 95% CI 0.36-0.63 at wave 1; 0.49, 95% CI 0.34-0.62 at wave 2), whereas for aAIx, we observed a diminished genetic effect (heritability 0.57, 95% CI 0.45-0.67 at wave 1; 0.37, 95% CI 0.21-0.51 at wave 2). Overlapping genetic factors explained a high proportion (0.88, 95% CI 0.61-1.00) of longitudinal covariance for aPWV, and had a relatively lower impact on aAIx (0.55, 95% CI 0.35-0.70). Genetic correlations of aPWV (r = 0.64, 95% CI 0.42-0.85) and aAIx (r = 0.70, 95% CI 0.52-0.87) between waves were lower than 1, suggesting a potential contribution of novel genetic variance on arterial stiffening.

CONCLUSION

Changes in aPWV and aAIx over time are largely genetically determined. Our results might stimulate further studies on genetic and epigenetic factors influencing the process of vascular ageing.

Twins Lead to the Prevention of Atherosclerosis: Preliminary Findings of International Twin Study 2009

Introduction

Atherosclerosis is an inflammatory process in which the artery wall thickens as a result of plaque deposition, but this process may be preceded by increased arterial stiffness. We sought to evaluate the influence of genetics and shared and unshared environmental components on the onset of atherosclerosis.

Methods

A total of 135 monozygotic (MZ) and 70 dizygotic (DZ) twin pairs (mean age 49 ± 16 years) underwent carotid intima media thickness (IMT; carotid analyzer) and arterial stiffness (augmentation index on brachial artery [ Aixbra], pulse wave velocity on aorta [ PWVao]; TensioMed Arteriograph) measurements.

Results

Age-adjusted intraclass correlations were greater in MZ than in DZ pairs for proximal right common carotid artery (CCA; MZ = 0.19, DZ = 0.06), proximal and distal left CCA (MZ = 0.27, DZ = 0.06; MZ = 0.27, DZ = 0.13, respectively), and proximal left internal carotid artery (ICA; MZ = 0.39, DZ = −0.54), suggesting a moderate genetic effect. Heritability was estimated to be 18% (95% confidence interval [CI] = 3–33) for proximal right CCA, 26% and 27% for proximal and distal left CCA, respectively, and 38% (95% CI = 26–49) for proximal left ICA. Regarding distal right CCA and proximal right ICA, no genetic effects were detected. Age-adjusted intraclass correlation of Aixbra and PWVao were 0.65 (95% CI = 0.55–0.72) and 0.46 (95% CI = 0.33–0.57) in MZ, 0.42 (95% CI = 0.24–0.57) and 0.28 (95% CI = 0.08–0.47) in DZ pairs; heritability 45% (95% CI = 12–71%) and 42% (95% CI = 2–57%) adjusted by age, respectively.

Conclusions

The investigated parameters appeared to be only moderately influenced by genetic factors. Environmental factors of relevance for these measures appeared not to be shared within family but related to individual experience (e.g., smoking habits, diet, and physical activity). Atherosclerosis detection at an early stage is necessary for treatment to prevent serious complications such as stroke and heart attack.

Association between hypertension in adolescents and the health risk factors of their parents: an epidemiological family study

Hypertension in adolescence may be a predictor of cardiovascular problems in adulthood. Therefore, verification of the factors associated with this condition in adolescence is important. The aim of this study was to analyze the relationship between hypertension in adolescents with hypertension and the sociodemographic characteristics and lifestyle of their parents. This study was conducted on 1231 adolescents, 1202 mothers, and 871 fathers. The blood pressure of the adolescents was measured with an oscillometric device. Details of parental hypertension, sociodemographic characteristics, and lifestyle were obtained by self-report. The prevalence of hypertension was higher among adolescents with older fathers and older mothers, with both parents reporting hypertension and with mothers who were overweight. In multivariable analysis, adolescents with older mothers (OR = 2.36; 95% confidence interval [CI] = 1.12-4.98), hypertensive mothers (OR = 2.22 [95% CI = 1.26-3.89]), and hypertensive fathers (OR = 1.70 [95% CI = 1.03-2.81]) were more likely to have hypertension. In the analysis that considered clusters of health risk factors, higher risks of hypertension were observed in adolescents whose mothers had four or more aggregated risk factors (OR = 2.53 [95% CI = 1.11-5.74]). In conclusion, there was a relationship between hypertension in adolescents and hypertension in their parents. However, an association between hypertension in adolescents and parental age and clusters of health risk factors was only observed for their mothers.

Bevacizumab-induced hypertension: Clinical presentation and molecular understanding

Bevacizumab is a vascular endothelial growth factor-A-specific angiogenesis inhibitor indicated as an adjunct to chemotherapy for the treatment of several types of cancer. Hypertension is commonly observed during bevacizumab treatment, and high-grade toxicity can limit therapy and lead to other cardiovascular complications. The factors that contribute to interindividual variability in blood pressure response to bevacizumab treatment are not well understood. In this review, we outline research efforts to understand the mechanisms and pathophysiology of hypertension resulting from bevacizumab treatment. Moreover, we highlight current knowledge of the pharmacogenetics of bevacizumab-induced hypertension, which may be used to develop strategies to prevent or minimize this toxicity.

Intrafamilial Aggregation and Heritability of Aortic Reflected (Backward) Waves Derived From Wave Separation Analysis

BACKGROUND

Although aortic wave reflection may be inherited, the extent to which indexes of wave reflection derived from wave separation analysis (reflected (backward) wave index (RI) and pressure (Pb)) show intrafamilial aggregation and heritability is uncertain. We therefore aimed to determine the intrafamilial aggregation and heritability of RI and Pb and compare these with indexes of pressure augmentation.

METHODS

Aortic Pb, RI, augmented pressure (Pa), and augmentation index (AIx) were determined using radial applanation tonometry and SphygmoCor software in 1,152 participants of 315 families (111 father-mother, 705 parent-child, and 301 sibling-sibling pairs) from an urban developing community of black Africans. Heritability estimates were determined from Statistical Analysis for Genetic Epidemiology software.

RESULTS

With appropriate adjustments, significant correlations were noted between parent-child pairs for Pb and Pa (P < 0.05 for all), but not for RI (P = 0.50) or AIx (P = 0.90) and between sib-sib pairs for Pb and Pa (P < 0.05), but not for RI (P = 0.54) or AIx (P = 0.14). No correlations for indexes of wave reflection were noted between fathers and mothers (P > 0.57). After adjustments, Pb (h2 = 0.24±0.07) and Pa (h2 = 0.23±0.07) (P < 0.001 for both) but not RI (h2 = 0.04±0.06, P = 0.27) or AIx (h2 = 0.10±0.07, P = 0.07) showed significant heritability.

CONCLUSIONS

Aortic reflected (backward) waves derived from either wave separation (Pb) or pulse wave analysis (Pa) show a similar degree of intrafamilial aggregation and heritability, but the use of RI or AIx may underestimate reflected wave effects.

Amino Acid Intakes Are Inversely Associated with Arterial Stiffness and Central Blood Pressure in Women

BACKGROUND

Although data suggest that intakes of total protein and specific amino acids (AAs) reduce blood pressure, data on other cardiovascular disease risk factors are limited.

OBJECTIVE

We examined associations between intakes of AAs with known mechanistic links to cardiovascular health and direct measures of arterial stiffness, central blood pressure, and atherosclerosis.

METHODS

In a cross-sectional study of 1898 female twins aged 18-75 y from the TwinsUK registry, intakes of 7 cardioprotective AAs (arginine, cysteine, glutamic acid, glycine, histidine, leucine, and tyrosine) were calculated from food-frequency questionnaires. Direct measures of arterial stiffness and atherosclerosis included central systolic blood pressure (cSBP), mean arterial pressure (MAP), augmentation index (AI), pulse wave velocity (PWV), and intima-media thickness (IMT). ANCOVA was used to assess the associations between endpoints of arterial stiffness and intake (per quintile), adjusting for potential confounders.

RESULTS

In multivariable analyses, higher intakes of total protein and 7 potentially cardioprotective AAs were associated with lower cSBP, MAP, and PWV. Higher intakes of glutamic acid, leucine, and tyrosine were most strongly associated with PWV, with respective differences of -0.4 ± 0.2 m/s (P-trend = 0.02), -0.4 ± 0.2 m/s (P-trend = 0.03), and -0.4 ± 0.2 m/s (P-trend = 0.03), comparing extreme quintiles. There was a significant interaction between AA intakes and protein source, and higher intakes of AAs from vegetable sources were associated with lower central blood pressure and AI. Higher intakes of glutamic acid, leucine, and tyrosine from animal sources were associated with lower PWV.

CONCLUSIONS

These data provide evidence to suggest that intakes of several AAs are associated with cardiovascular benefits beyond blood pressure reduction in healthy women. The magnitude of the observed associations was similar to those previously reported for other lifestyle factors. Increasing intakes of these AAs could be an important and readily achievable way to reduce cardiovascular disease risk.

Familial aggregation and childhood blood pressure

There is growing concern about elevated blood pressure (BP) in children. The evidence for familial aggregation of childhood BP is substantial. Twin studies have shown that a large part of the familial aggregation of childhood BP is due to genes. The first part of this review provides the latest progress in gene finding for childhood BP, focusing on the combined effects of multiple loci identified from the genome-wide association studies on adult BP. We further review the evidence on the contribution of the genetic components of other family risk factors to the familial aggregation of childhood BP including obesity, birth weight, sleep quality, sodium intake, parental smoking, and socioeconomic status. At the end, we emphasize the promise of using genomic-relatedness-matrix restricted maximum likelihood (GREML) analysis, a method that uses genome-wide data from unrelated individuals, in answering a number of unsolved questions in the familial aggregation of childhood BP.

Increased cardiovascular risk without generalized arterial dilating diathesis in persons who do not have abdominal aortic aneurysm but who are first-degree relatives of abdominal aortic aneurysm patients

There is a strong genetic predisposition towards abdominal aortic aneurysm (AAA), but it is unknown whether persons without AAA but with first-degree relatives who are AAA patients have a generalized dilating diathesis, defect arterial wall mechanics, or increased cardiovascular risk. The aim of the study was to investigate arterial diameters and wall mechanics at multiple arterial sites in these subjects and compare them with controls without a family history of AAA. This study included 118 first-degree relatives of patients with AAA and 66 controls (age: 40-80 years). The abdominal aorta, common carotid artery, common femoral artery, and popliteal artery were investigated by echo-tracking ultrasound. The relatives had no arterial dilatation, but they did tend to have smaller diameters than controls. Relatives had a higher heart rate, diastolic blood pressure, and mean arterial pressure than controls. The distensibility coefficient and the compliance coefficient were decreased in all arteries in male relatives, adjusted for age and smoking; these coefficients were normalized after adjustment for mean arterial pressure and heart rate. Female relatives had a lower compliance coefficient in the abdominal aorta, adjusted for age and smoking. After adjustment for mean arterial pressure and heart rate, the difference disappeared. No general arterial dilatation in relatives without AAA was found, supporting the hypothesis that the dilating diathesis is linked to the aneurysmal manifestation in the abdominal aorta. Although the threat of aneurysmal dilatation and rupture seems to be lacking in these subjects, heart rate, blood pressure, and arterial wall stiffness were all increased, which may indicate a higher risk of developing cardiovascular morbidity and mortality.

Heritability analyses show visit-to-visit blood pressure variability reflects different pathological phenotypes in younger and older adults: evidence from UK twins

BACKGROUND

Clinic and long-term average blood pressure (BP) are heritable traits with estimates of heritability ranging from 0.31 to 0.68. Long-term visit-to-visit BP variability (BPV) is emerging as a new cardiovascular risk predictor, though it is unclear if this is completely independent of BP. We hypothesize that BPV should demonstrate the same pattern of additive genetic, shared environmental and unique environmental variance as BP, if both are phenotypic surrogates.

METHOD

We studied 2889 twin pairs not on any BP-lowering therapy from the Twins UK cohort, and estimated the additive genetic variance for baseline BP, long-term average BP, BP trajectory (rate of change of BP in mmHg/year) and BPV (coefficient of variation and average real variability over an average of 3.2 visits). Heritability estimates were obtained by structural equation modelling adjusting for age, age, sex and BMI.

RESULTS

The heritabilities for baseline SBP and DBP were 0.51 (95% confidence interval 0.49, 0.53) and 0.56 (0.54, 0.58); long-term average SBP and DBP were 0.56 (0.53, 0.59) and 0.61 (0.58, 0.64); and systolic and diastolic trajectories over 10 years were 0.49 (0.46, 0.52) and 0.29 (0.27, 0.32), respectively. Both overall systolic and diastolic BPV showed no additive genetic variance contributing to the phenotypic variation, but after stratification by age, the younger subgroup (<51 years) showed heritability estimates of 0.44 (0.38, 0.50) for coefficient of variation and 0.35 (0.29, 0.41) for average real variability.

CONCLUSION

Age is a major factor that influences heritability estimation of BPV and it is likely that BPV in younger and older age groups may reflect different pathological phenotypes.

Heritability of arterial stiffness and carotid intima-media thickness: an Italian twin study

BACKGROUND AND AIMS

Carotid intima-media thickness (IMT) and arterial stiffness parameters, including aortic augmentation index (AIx) and pulse wave velocity (PWV), are independent predictors of stroke and cardiovascular disease. Genetic effects on these traits were never explored in a Mediterranean country. The present study aims to quantify the contribution of genes, environment and age to carotid IMT and aortic Aix and PWV.

METHODS AND RESULTS

The twin design was used. A total of 348 adult twins from the Italian Twin Register underwent measurements of carotid IMT and aortic PWV and AIx in three university hospitals located in Rome, Padua and Perugia. Carotid IMT was measured by B-mode ultrasound, aortic PWV and AIx by Arteriograph. Genetic modelling was performed to decompose total variance of traits into genetic, shared and unshared environmental and age components. For each phenotype, the best-fitting model included additive genetic, unshared environmental and age effects. For IMT, heritability was 0.32 (95% confidence interval (CI): 0.25-0.38), unshared environmental component was 0.25 (0.18-0.32) and age contribution was 0.44 (0.39-0.49). For AIx and PWV, heritabilities were 0.42 (0.29-0.55) and 0.49 (0.35-0.62), unshared environmental components were 0.31 (0.22-0.44) and 0.37 (0.26-0.51) and age contributions were 0.27 (0.16-0.39) and 0.14 (0.06-0.24), respectively.

CONCLUSION

This study shows substantial genetic and unshared environmental influences on carotid intima-media thickness and arterial stiffness and confirms the relevant role of age in the aetiology of these traits. Further support is provided for prevention and health promotion strategies based on modifiable factors.

Genetic influence on the relation between exhaled nitric oxide and pulse wave reflection

Nitric oxide has an important role in the development of the structure and function of the airways and vessel walls. Fractional exhaled nitric oxide (FE(NO)) is inversely related to the markers and risk factors of atherosclerosis. We aimed to estimate the relative contribution of genes and shared and non-shared environmental influences to variations and covariation of FE(NO) levels and the marker of elasticity function of arteries. Adult Caucasian twin pairs (n = 117) were recruited in Hungary, Italy and in the United States (83 monozygotic and 34 dizygotic pairs; age: 48 ± 16 SD years). FE(NO) was measured by an electrochemical sensor-based device. Pulse wave reflection (aortic augmentation index, Aix(ao)) was determined by an oscillometric method (Arteriograph). A bivariate Cholesky decomposition model was applied to investigate whether the heritabilities of FE(NO) and Aix(ao) were linked. Genetic effects accounted for 58% (95% confidence interval (CI): 42%, 71%) of the variation in FE(NO) with the remaining 42% (95%CI: 29%, 58%) due to non-shared environmental influences. A modest negative correlation was observed between FE(NO) and Aix(ao) (r = -0.17; 95%CI:-0.32,-0.02). FE(NO) showed a significant negative genetic correlation with Aix(ao) (r(g) = -0.25; 95%CI:-0.46,-0.02). Thus in humans, variations in FE(NO) are explained both by genetic and non-shared environmental effects. Covariance between FE(NO) and Aix(ao) is explained entirely by shared genetic factors. This is consistent with an overlap among the sets of genes involved in the expression of these phenotypes and provides a basis for further genetic studies on cardiovascular and respiratory diseases.

Genetic and environmental factors on the relation of lung function and arterial stiffness

BACKGROUND

An association between reduced lung function and increased cardiovascular risk has been reported, but the underlying mechanisms are unknown. The aim of this study was to assess the heritability of lung function and to estimate its genetic association with arterial stiffness.

METHODS

150 monozygotic and 42 dizygotic healthy Hungarian and American Caucasian twin pairs (age 43 ± 17 years) underwent spirometry (forced vital capacity/FVC/, forced expiratory volume in 1 s/FEV1/; MIR Minispir, USA); and their brachial and central augmentation indices (AIx), and aortic pulse wave velocity (PWV) were measured by oscillometric Arteriograph (TensioMed Ltd, Budapest, Hungary). Phenotypic correlations and bivariate Cholesky decomposition models were applied.

RESULTS

Age-, sex-, country- and smoking-adjusted heritability of FEV1, percent predicted FEV1, FVC and percent predicted FVC were 73% (95% confidence interval /CI/: 45-85%), 28% (95% CI: 0-67%), 68% (95% CI: 20-81%) and 45% (95% CI: 0-66%), respectively. Measured and percent predicted FVC and FEV1 values showed no significant phenotypic correlations with AIx or aortic PWV, except for phenotypic twin correlations between measured FEV1, FVC with brachial or aortic augmentation indices which ranged between -0.12 and -0.17. No genetic covariance between lung function and arterial stiffness was found.

CONCLUSIONS

Lung function is heritable and the measured FVC and FEV are phenotypically, but not genetically, associated with augmentation index, a measure of wave reflection. This relationship may in turn reveal further associations leading to a better mechanistic understanding of vascular changes in various airway diseases.

Higher anthocyanin intake is associated with lower arterial stiffness and central blood pressure in women

BACKGROUND

Although a high intake of some flavonoid subclasses may reduce cardiovascular disease mortality, data regarding the in vivo mechanisms of action are limited.

OBJECTIVE

We examined associations between habitual flavonoid intakes and direct measures of arterial stiffness, central blood pressure, and atherosclerosis.

DESIGN

In a cross-sectional study of 1898 women aged 18-75 y from the TwinsUK registry, intakes of total flavonoids and their subclasses (flavanones, anthocyanins, flavan-3-ols, polymers, flavonols, and flavones) were calculated from validated food-frequency questionnaires by using an updated and extended USDA database. Direct measures of arterial stiffness and atherosclerosis included central systolic blood pressure (cSBP), central diastolic blood pressure, mean arterial pressure (MAP), augmentation index, pulse wave velocity (PWV), and intima-media thickness.

RESULTS

In multivariate analyses, a higher anthocyanin intake was associated with significantly lower cSBP (mean ± SE: -3.0 ± 1.4 mm Hg for quintile 5 compared with quintile 1; P-trend = 0.02), MAP (-2.3 ± 1.2 mm Hg for quintile 5 compared with quintile 1; P-trend = 0.04), and PWV (-0.4 ± 0.2 m/s for quintile 5 compared with quintile 1; P-trend = 0.04), whereas a higher flavone intake was associated with a lower PWV (-0.4 ± 0.2 m/s for quintile 5 compared with quintile 1; P-trend = 0.04). Although a higher wine and berry intake was associated with a lower PWV, no associations were observed for total and other flavonoid subclasses.

CONCLUSIONS

These data, which include direct measures of arterial stiffness and thickness, suggest that higher intake of anthocyanins and flavones are inversely associated with lower arterial stiffness. The intakes of anthocyanins associated with these findings could be incorporated into the diet by the consumption of 1-2 portions of berries daily and are, therefore, relevant for public health strategies to reduce cardiovascular disease risk.

Heritability and Whole Genome Linkage of Pulse Pressure in Chinese Twin Pairs

Elevated pulse pressure is associated with cardiovascular disorders and mortality in various populations. The genetic influence on pulse pressure has been confirmed by heritability estimates using related individuals. Recently, efforts have been made in mapping genes that are linked to the phenotype. We report results on our heritability and linkage study conducted on the Chinese population in mainland China where cardiovascular and cerebrovascular diseases are becoming the leading cause of death. A total of 630 pairs of middle-aged Chinese twins were collected for heritability analysis, from which 63 dizygotic twin pairs were randomly selected for genome-wide linkage analysis using Affymetrix 6.0 SNP array. Regression analysis reconfirmed the significant effects of age, sex, and BMI on pulse pressure. Comparison of twin models suggested the parsimonious AE model as the best model with a heritability estimate of 0.45. Genome-wide non-parametric linkage analysis identified three significant linkage peaks on chromosome 11 (lod score 4.06 at 30.5 cM), chromosome 12 (lod score 3.97 at 100.7 cM), and chromosome 18 (lod score 4.01 at 70.7 cM) with the last two peaks closely overlapping with linkage peaks reported by two American studies. In addition, multiple regions with suggestive linkage were identified with many of them overlapping with published linkage regions. Our results provide both epidemiological and molecular genetic evidence for the genetic dissection of pulse pressure in the Chinese population, which could help in fine mapping and in characterizing genes that are involved in the regulation of pulse pressure.

Genome-wide linkage and association scans for pulse pressure in Chinese twins

Elevated pulse pressure (PP) is associated with cardiovascular disorders and mortality in various populations. The genetic influence on PP has been confirmed by heritability estimates using related individuals. Recently, efforts have been made by mapping genes that are linked to the phenotype. We report the results of our gene mapping studies conducted in the Chinese population in mainland China. The genome-wide linkage and association scans were carried out on 63 middle-aged dizygotic twin pairs using high-density markers. The linkage analysis identified three significant linkage peaks (all with a single point P<1e(-05)) on chromosome 11 (LOD core 4.06 at 30.5 cM), chromosome 12 (LOD score 3.97 at 100.7 cM) and chromosome 18 (LOD score 4.01 at 70.7 cM), with the last two peaks closely overlapping with linkage peaks reported by two American studies. Multiple regions with suggestive linkages were identified, with many of the peaks overlapping with published linkage regions. The genome-wide association analysis detected a suggestive association on chromosome 4 (rs17031508, P<8.34e(-08)) located within a wide region of suggestive linkage. Our results provide some evidence for genetic linkages and associations with PP in the Chinese population. Further investigation is warranted to replicate the findings and to explore the susceptibility loci or genes for PP.

A genetic risk variant for myocardial infarction on chromosome 6p24 is associated with impaired central hemodynamic indexes

BACKGROUND

Genome-wide association studies (GWAS) have identified novel variants associated with myocardial infarction (MI) in Caucasians. We hypothesized that those variants whose mechanism of risk is currently unknown, confer risk via pathways mediating arterial wave reflections which is an increasingly recognized risk factor for cardiovascular disease.

METHODS

Single-nucleotide polymorphisms (SNPs) at eight MI risk loci were genotyped and correlated with noninvasively determined pulse wave analysis (PWA)-derived central hemodynamic indexes (augmentation index (AIx); augmented pressure (AP); time to reflected wave (TrW) and central systolic blood pressure (SBP) and diastolic BP (DBP)) in two independent Caucasian populations including (i) those free of measured cardiovascular risk factors (n = 133) and (ii) a community-based population (n = 270).

RESULTS

Of the eight SNPs examined in the healthy group, the variants at loci 6p24 (AIx and AP both P < 0.001, TrW P = 0.02) and 21q22 (AIx P = 0.002, TrW P = 0.037) were significantly associated with PWA indexes. In the replication group, only the 6p24 variant correlated with these phenotypes (AIx P = 0.005, AP P = 0.049, TrW P = 0.013). In the pooled population (n = 403), no new associations were identified but the association with 6p24 and AIx remained significant even after Bonferroni correction and adjustment for covariates including age, mean arterial pressure, height, gender, glucose, cholesterol, body mass index (BMI), and smoking (AIx (P = 0.03)). Each copy of the risk allele C increased the AIx by 3.5%.

CONCLUSIONS

The GWAS discovered MI risk variant at 6p24 in the protein phosphatase 1 regulator gene (PHACTR1) is associated with adverse arterial wave reflection indexes and may mediate MI risk through this pathway.

Are Twins and Singletons Comparable? A Study of Disease-related and Lifestyle Characteristics in Adult Women

The classic twin study is sometimes described as “the perfect natural experiment” for the investigation of the aetiology of complex disease, but assumptions of the twin design need to be empirically tested if their results are to be considered unbiased and representative of singleton populations. In this study comparisons of disease and prevalence of lifestyle characteristics have been made between twin participants in the St Thomas' Hospital UK adult twin registry, the largest twin volunteer register in the UK for the study of diseases of ageing, and a parallel population-based study of singleton women. The only differences found were for weight, where monozygotic (MZ) twins were lighter and had a smaller variance than dizygotic (DZ) twins and singletons. For the other variables studied, volunteer twins were not found to differ from age-matched singleton women in distribution or prevalence of: bone mineral density, osteoarthritis, blood pressure, hypertensive drug use, height, history of hysterectomy and ovariectomy, menopausal status and current alcohol and overall tobacco consumption. We conclude that the results of twin studies can be generalised to singleton populations for these measures and disease outcomes.

Cohort Profile: TwinsUK and healthy ageing twin study

The UK's largest registry of adult twins, or TwinsUK Registry, started in 1992 and encompasses about 12000 volunteer twins from all over the United Kingdom. More than 70% of the registered twins have filled at least one detailed health questionnaire and about half of them undergone a baseline comprehensive assessment and two follow-up clinical evaluations. The most recent follow-up visit, known as Healthy Ageing Twin Study (HATS), involved 3125 female twins aged >40 years with at least one previous clinical assessment to enable inspection of longitudinal changes in ageing traits and their genetic and environmental components. The study benefits from several state-of-the-art OMICs studies including genome-wide association, next-generation genome and transcriptome sequencing, and epigenetic and metabolomic profiles. This makes our cohort as one of the most deeply phenotyped and genotyped in the world. Several collaborative projects in the field of epidemiology of complex disorders are ongoing in our cohort and interested researchers are encouraged to get in contact for future collaborations.

Peripheral and central augmentation indexes in relation to the CYP4F2 polymorphisms in Chinese

OBJECTIVE

Cytochrome (CYP) 4F2 isoform is a key metabolizing enzyme for the renal 20-hydroxyeicosatetraenoic acid (20-HETE), which, as an endogenous vasoconstrictor, may influence properties of the peripheral muscular arteries and arterioles. We, therefore, investigated the CYP4F2 polymorphisms in relation to arterial wave reflections, as measured by augmentation indexes (AIx) in Chinese.

METHODS

We performed arterial measurements by SphygmoCor and genotyped three CYP4F2 polymorphisms (V433M, rs3093089, and rs3093098) by PCR-restriction fragment length polymorphism in 1421 participants enrolled in the JingNing Population study. A replication study for the V433M polymorphism was performed in 924 Chinese recruited from a workplace setting. Urinary 20-HETE concentration was determined by ELISA in a randomly selected subsample of 318 JingNing individuals.

RESULTS

In spite of the fact that genetic associations were not significant (P ≥ 0.12) in all JingNing participants, there was significant (Pint ≤ 0.02) interaction of the V433M polymorphism with sex and pulse rate in relation to peripheral and central AIx. M433 allele carriers, compared with V433V homozygotes, had significantly greater peripheral (+5.0%, P = 0.0002) and central AIx (+3.2%, P = 0.001) in 693 men. The corresponding values were +2.7% (P = 0.04) and +1.9% (P = 0.04) in 490 individuals of the top tertile of pulse rate (≥ 76 beats/min), and were +4.0% (P = 0.02) and +3.3% (P = 0.02) in 315 replication participants with a pulse rate at least 76 beats/min. Urinary 20-HETE concentration was significantly higher (P = 0.002) in M433M (2.06 ng/ml) and V433M (1.13 ng/ml) individuals than in V433V homozygotes (0.98 ng/ml).

CONCLUSION

The CYP4F2 V433M polymorphism is associated with the size of arterial wave reflections in male Chinese, or individuals with a faster pulse rate.

Combined aliskiren-amlodipine treatment for hypertension in African Americans: clinical science and management issues

While it may seem at first that antihypertensive drug combinations run counter to the desire to 'personalize' the management of hypertension, the best combinations have predictable efficacy in different individuals and subpopulations. Race is probably not a valid surrogate for clinically meaningful genetic variation or guide to therapy. Most guidelines suggest similar blood pressure goals for different races but drug treatment recommendations have diverged. In the United States, race is not considered to be a major factor in drug choice, but in England and other countries, initial therapy with renin-angiotensin system blocking drugs is not recommended in Blacks. In this review we: (1) examine new trends in race-based research; (2) emphasize the weaknesses of race-based treatment recommendations; and (3) explore the effects of a new combination, renin inhibition (aliskiren) and amlodipine, in African Americans.

The genetic and environmental etiology of sympathetic and parasympathetic activity in children

The present study examines the genetic and environmental etiology of the associations among respiratory sinus arrhythmia (RSA), heart rate (HR), skin conductance level (SCL), and non-specific skin conductance responses (NS-SCR)-measures that purportedly index the parasympathetic and sympathetic branches of the autonomic nervous system. The sample was drawn from a cohort of 1,219 preadolescent twins (aged 9-10). Multivariate analyses of the data were conducted using structural equation modeling. Almost all genetic and environmental influences on the measures acted through two latent factors. The first latent factor was largely responsible for the variance in heart rate, SCL and NS-SCR, reflecting sympathetic activity, and its proportions of variance due to genetic and shared environmental influences were 27 and 28% in males, and 31 and 41% in females, respectively. The second latent factor accounted for the variance in RSA and heart rate, reflecting parasympathetic activity; genetic and shared environmental factors explained 27 and 23% of the variance in males, respectively, and 35 and 18% of the variance in females. Measurement-specific genetic effects accounted for 14-27% of the total variance in RSA and SCL, and measurement-specific shared environmental effects accounted for 10-12% in SCL. In general, the validity of separate sympathetic and parasympathetic constructs was supported.

Racial Differences in Relation Between Carotid and Radial Augmentation Index

BACKGROUND: Augmented central artery wave reflection is a cardiovascular disease risk factor. Augmentation index (AI) obtained from peripheral artery waveforms provides qualitatively similar information to AI from central artery waveforms. Little information is available, however, regarding the influence of racial difference in association between central and peripheral AI. METHODS: We studied 47 White adults (45+/-17 yr, 20 women) and 94 age-matched Asian adults (45+/-14 yr, 42 women). RESULTS: The White group was significantly taller than the Asian group, whereas there were no significant group differences in blood pressure and heart rate. Carotid and radial AI tended to be lower in White compared with Asian adults (P<0.10 for both). Such tendency disappeared when the difference in height was taken into account using ANCOVA (P=0.84 and P=0.77, respectively). Radial AI was strongly and positively correlated with carotid AI in White adults (r=0.75, P<0.0001) as well as in Asian adults (r=0.82, P<0.0001). The slope and intercept of linear regression line between radial and carotid AI of White adults were highly comparable with those of Asian adults. CONCLUSION: AI in the conveniently located peripheral vasculature may provide a surrogate measure of central AI irrespective of difference in race (e.g., Asian vs. White populations).

Increased wave reflection rather than central arterial stiffness is the main determinant of raised pulse pressure in women and relates to mismatch in arterial dimensions: a twin study

OBJECTIVES

Our aim was to examine the relative contributions of the first systolic shoulder (P1) and augmentation pressure (DeltaP(aug)) to central pulse pressure (cPP), their relation to central arterial stiffness (pulse wave velocity [PWV]) and arterial diameters, and their respective heritability estimates.

BACKGROUND

cPP is augmented above P1 by DeltaP(aug) due to pressure waves reflected from the periphery of the circulation.

METHODS

Women (n = 496) from the Twins UK adult twin registry (112 monozygotic, 135 dizygotic pairs) age 21 to 81 years were studied. cPP, P1, and DeltaP(aug) were estimated using the SphygmoCor system (Atcor, West Ryde, Australia) from transformed radial waveforms. Carotid-femoral PWV was measured using the same system. Aortic and femoral artery diameters were measured by ultrasonography. Heritability was estimated using structural equation modeling.

RESULTS

P1 and DeltaP(aug) accounted for 22% and 76%, respectively, of the variance in cPP. After adjustment for mean arterial pressure and heart rate, P1 strongly independently positively correlated with PWV (standardized regression coefficient, beta = 0.4, p < 0.0001), whereas DeltaP(aug) did not independently correlate with PWV but independently negatively correlated with the ratio of the diameter of the femoral to that of the abdominal aorta (beta = -0.12, p < 0.001). Estimates of heritability (h(2)) of cPP, PWV, P1, and DeltaP(aug) were 0.43, 0.34, 0.31, and 0.62, respectively, after adjustment for mean arterial pressure and heart rate.

CONCLUSIONS

These results suggest that, in women, DeltaP(aug) is highly heritable, is associated with the ratio of distal to proximal arterial diameters, and, independent of PWV, is a major determinant of cPP.

Association between arterial stiffness and variations in oestrogen-related genes

Increased arterial stiffness and wave reflection have been identified as cardiovascular disease risk factors. In light of significant sex differences and the moderate heritability of vascular function measures, we hypothesized that variation in the genes coding for estrogen receptors alpha (ESR1) and beta (ESR2) and aromatase (CYP19A1) is associated with aortic stiffness and pressure wave reflection as measured by noninvasive arterial tonometry. 1261 unrelated Framingham Offspring Study participants who attended the 7^th examination cycle (mean age 62±10 years, 52% women) and had arterial tonometry and genotyping data were included in the study. ANCOVA was used to assess the association of polymorphisms with forward wave amplitude, augmented pressure, augmentation index, carotid-femoral pulse wave velocity, and mean arterial pressure with adjustment for potential confounders. In the sex-pooled analysis, those homozygous for the minor allele at any of four ESR1 variants that were in strong linkage disequilibrium ((TA)_n, rs2077647, rs2234693 and rs9340799) had on average 18% higher augmented pressure and 16% greater augmentation index compared to carriers of one or two major alleles (p=0.0002–0.01). A similar magnitude of association was detected in those homozygous for the common allele at two ESR2 SNPs (p=0.007–0.02). Our results are consistent with the hypothesis that variation in ESR1 and ESR2, but not CYP19A1, is associated with increased wave reflection, which may contribute to previously demonstrated associations between these variants and adverse clinical events. Our findings will need to be replicated in additional cohorts.

Left ventricular mass and incident hypertension in individuals with initial optimal blood pressure: the Strong Heart Study

OBJECTIVE

Metabolic abnormalities have been shown to predict 8-year incident arterial hypertension in individuals with optimal blood pressure. As echocardiographic left ventricular mass has also been reported to predict incident hypertension in individuals with baseline blood pressure of less than 140/90 mmHg, we determined whether left ventricular mass predicts 4-year incident hypertension also in individuals with initial optimal blood pressure (<120/80 mmHg), independent of metabolic factors influencing blood pressure.

METHODS

We studied 777 of 3257 members of the American Indian population-based Strong Heart Study cohort with optimal blood pressure (34% men, 45% obese, and 35% diabetic), aged 57 +/- 7 years, and without prevalent cardiovascular disease.

RESULTS

Over 4 years, 159 individuals (20%, group H) developed hypertension (blood pressure >/=140/90 mmHg). They had a greater baseline BMI, waist girth, and blood pressure (112/69 vs. 109/68 mmHg, all P < 0.03) than those remaining normotensive (group N), with similar lipid profile and renal function. At baseline, left ventricular mass was significantly greater in group H than in group N (P < 0.004). The difference in left ventricular mass was confirmed after controlling for initial BMI, systolic blood pressure, homeostatic model assessment index, and diabetes. The probability of incident hypertension increased by 36% for each standard deviation of left ventricular mass index (P = 0.006), independent of covariates. Participants with left ventricular mass of more than 159 g (75th percentile of distribution) had 2.5-fold (95% confidence interval, 1.4-3.6; P < 0.001) higher adjusted risk of incident hypertension than those below this value.

CONCLUSION

Left ventricular mass predicts incident arterial hypertension in individuals with initially optimal blood pressure. This association is independent of body build, prevalent diabetes, and initial blood pressure.

Educational attainment and the heritability of self-reported hypertension among male Vietnam-era twins

OBJECTIVE

To investigate the potential for gene x environment interaction in hypertension by examining the extent to which educational attainment modifies the heritability of hypertension in male twins. Prior twin and family studies have established that hypertension runs in families and is heritable. In addition, epidemiological research indicates that the prevalence of hypertension differs by socioeconomic factors, such as educational attainment.

METHODS

Twin structural equation modeling was used to examine educational attainment as a moderator of heritability of hypertension. Participants were 4301 monozygotic and 3414 dizygotic male Vietnam-era twins who provided data on both education (in years) and self-report of physician diagnosis of hypertension or medication usage.

RESULTS

Heritability was 17 points lower among co-twins concordant for educational attainment of < or =14 years (0.46, 95% CI = 0.32-0.57) relative to co-twins concordant for >14 years of education (0.63, 95% CI = 0.54-0.71). The significant moderation of the heritability (p = .04) was confirmed in twin models examining educational attainment as a continuous moderator of hypertension.

CONCLUSIONS

These results demonstrate that the expression of genetic vulnerability to hypertension can vary as a function of environmental factors, including education level, and that nongenetic pathways may differentially contribute to risk among those with fewer years of education.

Heritability and intrafamilial aggregation of arterial characteristics

BACKGROUND

We investigated the heritability and familial aggregation of various indexes of arterial stiffness and wave reflection and we partitioned the phenotypic correlation between these traits into shared genetic and environmental components.

METHODS

Using a family-based population sample, we recruited 204 parents (mean age, 51.7 years) and 290 offspring (29.4 years) from the population in Cracow, Poland (62 families), Hechtel-Eksel, Belgium (36), and Pilsen, the Czech Republic (50). We measured peripheral pulse pressure (PPp) sphygmomanometrically at the brachial artery; central pulse pressure (PPc), the peripheral augmentation indexes (PAIxs) and central augmentation indexes (CAIxs) by applanation tonometry at the radial artery; and aortic pulse wave velocity (PWV) by tonometry or ultrasound. In multivariate-adjusted analyses, we used the ASSOC and PROC GENMOD procedures as implemented in SAGE and SAS, respectively.

RESULTS

We found significant heritability for PAIx, CAIx, PPc and mean arterial pressure ranging from 0.37 to 0.41; P < or = 0.0001. The method of intrafamilial concordance confirmed these results; intrafamilial correlation coefficients were significant for all arterial indexes (r > or = 0.12; P < or = 0.02) with the exception of PPc (r = -0.007; P = 0.90) in parent-offspring pairs. The sib-sib correlations were also significant for CAIx (r = 0.22; P = 0.001). The genetic correlation between PWV and the other arterial indexes were significant (rhoG > or = 0.29; P < 0.0001). The corresponding environmental correlations were only significantly positive for PPp (rhoE = 0.10, P = 0.03).

CONCLUSION

The observation of significant intrafamilial concordance and heritability of various indexes of arterial stiffness as well as the genetic correlations among arterial phenotypes strongly support the search for shared genetic determinants underlying these traits.

Genetic markers of vascular aging

Age is a powerful determinant of cardiovascular risk, being associated with a number of deleterious changes in the cardiovascular system. Increased arterial stiffness is an almost ubiquitous accompaniment of aging. However, there is significant variability in age-related arterial changes between individuals likely due, in part, to genetic factors. Measures of arterial stiffness such as pulse pressure and aortic pulse wave velocity have been shown to be heritable, indicating that genetic factors play a role in the interindividual variation of these phenotypes. Linkage analyses in related individuals have identified several genomic regions that may influence measures of arterial stiffness, and numerous association studies have investigated whether polymorphisms in candidate genes are related to this phenotype. Genome-wide association studies using 500,000 single nucleotide polymorphisms or more are now feasible and will accelerate the discovery of specific genetic polymorphisms that influence vascular aging/stiffness. Such findings will facilitate the development of novel therapies to retard vascular aging.