Population-based twin study of the effects of migration from Finland to Sweden on endothelial function and intima-media thickness

A Review of Vascular Traits and Assessment Techniques, and Their Heritability

Various tools are available to assess atherosclerosis, arterial stiffening, and endothelial function. They offer utility in the assessment of hypertensive phenotypes, in cardiovascular risk prediction, and as surrogate endpoints in clinical trials. We explore the relative influence of participant genetics, with reference to large-scale genomic studies, population-based cohorts, and candidate gene studies. We find heritability estimates highest for carotid intima-media thickness (CIMT 35–65%), followed by pulse wave velocity as a measure of arterial stiffness (26–43%), and flow mediated dilatation as a surrogate for endothelial function (14–39%); data were lacking for peripheral artery tonometry. We furthermore examine genes and polymorphisms relevant to each technique. We conclude that CIMT and pulse wave velocity dominate the existing evidence base, with fewer published genomic linkages for measures of endothelial function. We finally make recommendations regarding planning and reporting of data relating to vascular assessment techniques, particularly when genomic data are also available, to facilitate integration of these tools into cardiovascular disease research.

Examining the Brachial Artery Reactivity Curve Measured by B-Mode Ultrasound in the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) Pilot Study

Brachial artery reactivity was assessed in the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) Pilot Study using B-mode ultrasound. Carotid artery intima-media thickness (CIMT), a known subclinical predictor of cardiovascular disease, also was examined in relation to brachial artery reactivity. A continuous scan was performed on the artery for 8 min (1 min of baseline, 4 min of cuff inflation at 40 mmHg greater than systolic pressure, 3 min after cuff release).

The sample for analysis (n = 78; 43 men, 35 women) consisted of active-duty police officers from a larger sample in the BCOPS pilot study. Means and standard deviations (SDs) stratified by gender were calculated, along with Pearson's correlations between brachial variables, and with CIMT. Arterial diameters (baseline, pre-cuff release, peak) were significantly different ( p < 0.001) between men and women. Peak arterial dilation occurred at 50.77 ± 21.97 sec (49.67 ± 20.22 cardiac cycles) after cuff deflation in men, and 44.66 ± 24.07 sec (44.57 ± 20.36 cardiac cycles) after cuff deflation in women. Mean common carotid artery IMT and mean maximum IMT of all carotid sites were significantly correlated ( p < 0.01) in men (r = 0.691) and women (r = 0.450). Brachial reactivity measures were inversely correlated with CIMT in women, and in contrast, positively correlated in men.

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.

Genetic Regulation of Endothelial Vasomotor Function

The endothelium plays an important role in the regulation of vasomotor tone and the maintenance of vascular integrity. Endothelial dysfunction, i.e., impaired endothelial dependent dilation, is a fundamental component of the pathogenesis of cardiovascular disease. Although endothelial dysfunction is associated with a number of cardiovascular disease risk factors, those risk factors are not the only determinants of endothelial dysfunction. Despite knowing many molecules involved in endothelial signaling pathways, the genetic contribution to endothelial function has yet to be fully elucidated. This mini-review summarizes current evidence supporting the genetic contribution to endothelial vasomotor function. Findings from population-based studies, association studies for candidate genes, and unbiased large genomic scale studies in humans and rodent models are discussed. A brief synopsis of the current studies addressing the genetic regulation of endothelial responses to exercise training is also included.

Higher usual alcohol consumption was associated with a lower 41-y mortality risk from coronary artery disease in men independent of genetic and common environmental factors: the prospective NHLBI Twin Study

BACKGROUND

Evidence that alcohol consumption is inversely associated with long-term coronary artery disease (CAD) mortality independent of genetic and early life environmental factors is lacking.

OBJECTIVE

We evaluated whether alcohol consumption was prospectively associated with CAD mortality risk independent of familial factors.

DESIGN

In total, 843 male twins (396 pairs and 51 unpaired twins) aged 42-55 y (mean: 48 y) without baseline CAD reported beer, wine, and spirits consumption at baseline (1969-1973) and were followed up to 2010 in the prospective National Heart, Lung, and Blood Institute Twin Study. Data on usual alcohol consumption over the past year were collected. Outcome was time to event, where the primary event was death from CAD and secondary events were death from cardiovascular disease and all causes. HRs were estimated by using frailty survival models, both overall and within-pair.

RESULTS

There were 129 CAD deaths and 219 cardiovascular deaths during 41 y of follow-up. In the whole cohort, after adjustment for caloric intake and cardiovascular disease risk factors, overall HRs per 10-g increment in alcohol intake were 0.94 (95% CI: 0.89, 0.98) for CAD and 0.97 (95% CI: 0.93, 1.00) for cardiovascular mortality. The within-pair adjusted HRs for a twin with 10-g higher daily alcohol consumption than his co-twin were 0.90 (95% CI: 0.84, 0.97) for CAD and 0.95 (95% CI: 0.90, 1.00) for cardiovascular disease mortality in the cohort pooled by zygosity, which remained similar among monozygotic twins. All 3 beverage types tended to be associated with lower CAD mortality risk within-pair to a similar degree. Alcohol consumption was not associated with total mortality risk overall or within-pair.

CONCLUSION

Higher usual alcohol consumption is associated with lower CAD mortality risk, independent of germline and early life environment and adulthood experience shared among twins, supporting a possible causal role of alcohol consumption in lowering CAD death risk. This trial was registered at clinicaltrials.gov as NCT00005124.

Angle between the common and internal carotid arteries detected by ultrasound is related to intima-media thickness among those with atherosclerotic disease

OBJECTIVES

Although carotid artery structural variations have been detected by ultrasound, their clinical significance is not fully understood. The objective of this study was to determine whether the angle between the common carotid artery (CCA) and the internal carotid artery (ICA), designated angle α, an ultrasound-detectable carotid artery structural variation, is related to carotid artery intima-media thickness (IMT), a surrogate marker for carotid atherosclerosis.

METHODS

As a cross-sectional study, we measured angle α in routine carotid artery ultrasounds from 176 subjects (130 men) with atherosclerotic disease/risk factors that attended Kouseiren Hospital in Kagoshima City, Japan between August 2007 and April 2009. We evaluated the correlation between the angle α and CCA- or ICA-IMT.

RESULTS

Angle α was weakly correlated with age but significantly correlated with ICA-IMT. The correlation was stronger in subjects with an ICA-IMT ≥ 0.5 mm than in those with an ICA-IMT < 0.5 mm (Right side r = 0.475 vs. 0.246, Left side r = 0.498 vs. 0.301, respectively). Upon multivariate logistic regression analysis, angle α and serum low-density lipoprotein cholesterol were independent explanatory variables for ICA-IMT.

CONCLUSION

Angle α is related to ICA-IMT in subjects with atherosclerotic disease or risk factors in this study.

Genetic profiles in ischaemic stroke

Stroke represents a clinical syndrome rather than a single disease. A number of stroke subtypes can be distinguished based on careful phenotyping, with each of these having distinct and overlapping risk factor profiles. Recent evidence has suggested that genetics plays an important part in stroke risk, with at least 2 genes specific to stroke risk directly now having been identified. This review will explore our current understanding of the genetics underlying stroke risk and whether this information is currently useful in a clinical setting for patient benefit.

New quantitative trait loci for carotid atherosclerosis identified in an intercross derived from apolipoprotein E-deficient mouse strains

Carotid atherosclerosis is the primary cause of ischemic stroke. To identify genetic factors contributing to carotid atherosclerosis, we performed quantitative trait locus (QTL) analysis using female mice derived from an intercross between C57BL/6J (B6) and BALB/cJ (BALB) apolipoprotein E (Apoe^−/−) mice. We started 266 F₂ mice on a Western diet at 6 wk of age and fed them the diet for 12 wk. Atherosclerotic lesions in the left carotid bifurcation and plasma lipid levels were measured. We genotyped 130 microsatellite markers across the entire genome. Three significant QTLs, Cath1 on chromosome (Chr) 12, Cath2 on Chr5, and Cath3 on Chr13, and four suggestive QTLs on Chr6, Chr9, Chr17, and Chr18 were identified for carotid lesions. The Chr6 locus replicated a suggestive QTL and was named Cath4. Six QTLs for HDL, three QTLs for non-HDL cholesterol, and three QTLs for triglyceride were found. Of these, a significant QTL for non-HDL on Chr1 at 60.3 cM, named Nhdl13, and a suggestive QTL for HDL on ChrX were new. A significant locus for HDL (Hdlq5) was overlapping with a suggestive locus for carotid lesions on Chr9. A significant correlation between carotid lesion sizes and HDL cholesterol levels was observed in the F₂ population (R = −0.153, P = 0.0133). Thus, we have identified several new QTLs for carotid atherosclerosis and the locus on Chr9 may exert effect through interactions with HDL.

Comparison of stroke mortality in Finnish-born migrants living in Sweden 1970-1999 and in Swedish-born individuals

A limited number of studies have been found on stroke mortality in migrants showing higher mortality for some groups. Influence of time of residence has been studied by one research group. An earlier study showed a significantly higher number of deaths in Diseases of the circulatory system in Finnish migrants compared with native Swedes. To test the hypothesis of a higher mortality in and a decrease in mortality over time in stroke among Finnish migrants in Sweden. The study was based on National Population data, the study population included 321,407 Swedish and 307,174 foreign born persons living in Sweden 1987-1999. Mean age was lower at time for death for Finnish migrants than native Swedes, men 5.1 years difference and women 2.3 years. The difference decreased over time. The risk of death by stroke was higher for migrants with short time of residence than with long time (≤10 years, OR 1.61-1.36 vs ≥11 year, OR 1.18). Migrants with short time of residence died 9.8-5.3 years earlier than native Swedes. The hypothesis was confirmed and an indication of adjustment to life in the new country was found. International studies show similar results for other migrant groups but further studies are needed to verify if the same pattern can be found in other migrants groups in Sweden and to generalise the findings.

Work and health among immigrants and native Swedes 1990-2008: a register-based study on hospitalization for common potentially work-related disorders, disability pension and mortality

Background

There are many immigrants in the Swedish workforce, but knowledge of their general and work-related health is limited. The aim of this register-based study was to explore whether documented migrant residents in Sweden have a different health status regarding receipt of a disability pension, mortality and hospitalization for lung, heart, psychiatric, and musculoskeletal disorders compared with the native population, and if there were variations in relation to sex, geographical origin, position on the labor market, and time since first immigration.

Methods

This study included migrants to Sweden since 1960 who were 28–47 years old in 1990, and included 243 860 individuals. The comparison group comprised a random sample of 859 653 native Swedes. These cohorts were followed from 1991 to 2008 in national registers. The immigrants were divided into four groups based on geographic origin. Hazard ratios for men and women from different geographic origins and with different employment status were analyzed separately for the six outcomes, with adjustment for age, education level, and income. The influence of length of residence in Sweden was analyzed separately.

Results

Nordic immigrants had increased risks for all investigated outcomes while most other groups had equal or lower risks for those outcomes than the Swedes. The lowest HRs were found in the EU 15+ group (from western Europe, North America, Australia and New Zealand). All groups, except Nordic immigrants, had lower risk of mortality, but all had higher risk of disability pension receipt compared with native Swedes. Unemployed non-Nordic men displayed equal or lower HRs for most outcomes, except disability pension receipt, compared with unemployed Swedish men. A longer time since first immigration improved the health status of men, while women showed opposite results.

Conclusions

Employment status and length of residence are important factors for health. The contradictory results of low mortality and high disability pension risks need more attention. There is great potential to increase the knowledge in this field in Sweden, because of the high quality registers.

Genetics of common polygenic ischaemic stroke: current understanding and future challenges

Stroke is the third commonest cause of death and the major cause of adult neurological disability worldwide. While much is known about conventional risk factors such as hypertension, diabetes and incidence of smoking, these environmental factors only account for a proportion of stroke risk. Up to 50% of stroke risk can be attributed to genetic risk factors, although to date no single risk allele has been convincingly identified as contributing to this risk. Advances in the field of genetics, most notably genome wide association studies (GWAS), have revealed genetic risks in other cardiovascular disease and these techniques are now being applied to ischaemic stroke. This paper covers previous genetic studies in stroke including candidate gene studies, discusses the genome wide association approach, and future techniques such as next generation sequencing and the post-GWAS era. The review also considers the overlap from other cardiovascular diseases and whether findings from these may also be informative in ischaemic stroke.

Impact of exercise training on endothelial function and body composition in young people: a study of mono- and di-zygotic twins

Flow mediated dilation (FMD) is a surrogate marker of arterial function which can be improved by exercise training. To date, no study has assessed the magnitude of FMD changes in response to exercise training between groups of mono- (MZ) and di-zygotic (DZ) twins. The purpose of this study was therefore to compare FMD in MZ- and DZ twins before and after identical exercise training interventions. At baseline, FMD was assessed using high resolution Duplex ultrasound in 12 twin pairs (6 MZ pairs 13.5 ± 0.8 years, 6 DZ pairs 13.4 ± 0.8 years). Twins completed 8 weeks of exercise training (65-85% HR(max)), consisting of three 45-min sessions per week. Change (Δ) scores were entered into twin versus twin intraclass correlation analyses by group. Change in %body fat (r = 0.63, P = 0.05) was significantly correlated in the MZ, but not the DZ group (r = 0.31, P = 0.23). Change in FMD was also highly correlated in MZ (r = 0.74, P = 0.02) but not in the DZ group (r = 0.37, P = 0.18). Heritability of ΔFMD was estimated at 0.74. Exercise induced changes in FMD were similar within sets of monozygotic twins but not dizygotic twins. These data suggest that a significant portion of the arterial function response to exercise training may be genetically determined.

Genetic variation in LPAL2, LPA, and PLG predicts plasma lipoprotein(a) level and carotid artery disease risk

BACKGROUND AND PURPOSE

lipoprotein(a) [Lp(a)] level is an established risk factor for coronary artery disease and has been implicated in carotid artery disease (CAAD). The relationship between genetic variation in the LPA gene region and CAAD risk remains unknown.

METHODS

we genotyped single nucleotide polymorphisms (SNPs) in the LPAL2, LPA, and PLG regions in 530 individuals with severe CAAD and 770 controls and kringle IV type 2 (KIV2) repeat length in a subset of 90 individuals.

RESULTS

nine SNPs collectively accounted for 30% of the variance in Lp(a) level. Six SNPs were associated with Lp(a) level after accounting for KIV2 copy number, and the dominant KIV2 allele combined with these markers explained 60% of the variance in Lp(a) level. Five SNPs, including rs10455872, which had an odds ratio of 2.1 per minor allele and haplotypes formed by rs10455872, rs6919346, and rs3123629, were significant predictors of CAAD. After accounting for Lp(a) level, all evidence of CAAD-genotype association in the LPA region was eliminated.

CONCLUSIONS

LPA region SNPs capture some but not all of the effect of KIV2 repeat length on Lp(a) level. There are associations between LPA region SNPs and CAAD that appear to be attributable to effects on Lp(a) level.

Heritability of arterial function, fitness, and physical activity in youth: a study of monozygotic and dizygotic twins

OBJECTIVES

To examine the role of heredity in determining flow-mediated dilation in young people by comparing conduit artery endothelial function in monozygotic and dizygotic twins. We also determined relationships between physical activity and fitness in each twin subset.

STUDY DESIGN

Flow-mediated dilation was assessed with high-resolution ultrasonography of the brachial artery in 22 twin pairs (11 monozygotic pairs 13.3 ± 1.6 years, 11 dizygotic pairs 13.6 ± 1.6 years). Fitness was assessed as peak oxygen uptake during an incremental treadmill test. Physical activity was measured with accelerometry. Twin versus twin intraclass correlations were performed for both groups.

RESULTS

Flow-mediated dilation was significantly correlated in monozygotic twins only (r = 0.60, P = .02). Heritability of flow-mediated dilation was estimated at 0.44. Total PA time (monozygotic r = 0.77, dizygotic r = 0.60, P < .05) and light physical activity time (monozygotic r = 0.67, dizygotic r = 0.63, P < .05) correlated significantly in both groups. The peak oxygen uptake (r = 0.84, P < .01) was correlated only in monozygotic twins.

CONCLUSION

Genetic factors appear to be responsible for a modest portion of the flow-mediated dilation response, suggesting that flow-mediated dilation can be influenced by environmental factors.

Genomewide linkage and peakwide association analyses of carotid plaque in Caribbean Hispanics

BACKGROUND AND PURPOSE

Atherosclerosis is a complex subclinical cardiovascular disorder with a substantial genetic component. This study sought to identify genetic loci influencing carotid plaque in 2 independent samples.

METHODS

B-mode ultrasound was performed to determine the presence and area of carotid plaque. Variance components analysis was used to test for linkage using 383 autosomal microsatellite markers in 1308 subjects from 100 Dominican families. Multiple linear and logistic regression models were used to investigate the association between plaque traits and 18,904 single nucleotide polymorphisms under the 1-logarithm of odds unit down regions of linkage peaks in an independent community-based data set (N = 941, 41% Dominicans) from the Northern Manhattan Study.

RESULTS

After adjustment for age, hypertension, diabetes mellitus, cigarette pack-years, body mass index, and waist-to-hip ratio, significant heritability was detected for plaque presence (h² = 0.50 ± 0.14, P < 0.0001) and plaque area (h²=0.17 ± 0.04, P < 0.0001). Quantitative and dichotomous trait linkage analyses obtained similar results and identified 4 regions with multipoint logarithm of odds scores ≥ 2.00 on 7q36, 11p15, 14q32, and 15q23. In the association analysis of the 4 linkage peaks, several single nucleotide polymorphisms in or near SOX6, FSD2, AP3S2, EFTUD1, and MYOD1 were associated with carotid plaque traits with a nominal P ≤ 0.0005 in the Northern Manhattan Study data set and with a P ≤ 0.01 in Northern Manhattan Study Dominican subset.

CONCLUSIONS

Carotid plaque has considerable heritability and may be influenced by loci on chromosomes 11p15, 14q32, and 15q23. The SOX6 gene within the bone morphogenic protein pathway could be a candidate for carotid plaque. Larger independent studies are needed to validate these findings.

Genetics studies in ischaemic stroke

Conventional risk factors such as high blood pressure account for a significant proportion of stroke risk, but much stroke risk remains unexplained. Epidemiological evidence suggests genetic predisposition accounts for some of this unexplained risk. Many candidate genes association studies have been performed but have lead to largely disappointing results. The genome-wide association study (GWAS) approach allows novel associations to be identified with as many as one million polymorphisms (genetic variants) across the genome. It has been successfully applied to other complex diseases, including other cardiovascular diseases, but stroke has lagged behind. A number of GWAS projects in stroke are now underway. Genetic variants originally identified using the GWAS approach in atrial fibrillation and coronary artery disease have been shown to also confer an increased risk of stroke. These associations have been with specific subtypes of stroke, emphasising the importance of accurate stroke subtyping. The use of intermediate phenotypes for stroke, such as white matter hyperintensities on MRI and carotid intima-media thickness, is also discussed.

Unravelling the genetics of ischaemic stroke

Hugh Markus discusses genetic factors in stroke risk, and emphasizes the importance of large sample studies and rigorous replication of results in genetic stroke research.

Analysis of recently identified dyslipidemia alleles reveals two loci that contribute to risk for carotid artery disease

Background

Genome-wide association studies have identified numerous single nucleotide polymorphisms (SNPs) affecting high density lipoprotein (HDL) or low density lipoprotein (LDL) cholesterol levels; these SNPs may contribute to the genetic basis of vascular diseases.

Results

We assessed the impact of 34 SNPs at 23 loci on dyslipidemia, key lipid sub-phenotypes, and severe carotid artery disease (CAAD) in a case-control cohort. The effects of these SNPs on HDL and LDL were consistent with those previously reported, and we provide unbiased estimates of the percent variance in HDL (3.9%) and LDL (3.3%) explained by genetic risk scores. We assessed the effects of these SNPs on HDL subfractions, apolipoprotein A-1, LDL buoyancy, apolipoprotein B, and lipoprotein (a) and found that rs646776 predicts apolipoprotein B level while rs2075650 predicts LDL buoyancy. Finally, we tested the role of these SNPs in conferring risk for ultrasonographically documented CAAD stenosis status. We found that two loci, chromosome 1p13.3 near CELSR2 and PSRC1 which contains rs646776, and 19q13.2 near TOMM40 and APOE which contains rs2075650, harbor risk alleles for CAAD.

Conclusion

Our analysis of 34 SNPs contributing to dyslipidemia at 23 loci suggests that genetic variation in the 1p13.3 region may increase risk of CAAD by increasing LDL particle number, whereas variation in the 19q13.2 region may increase CAAD risk by promoting formation of smaller, denser LDL particles.

Migration at early age from a high to a lower coronary heart disease risk country lowers the risk of subclinical atherosclerosis in middle-aged men

BACKGROUND

Study of migrants offers a natural model to assess environmental risk of coronary heart disease (CHD) in countries differing in CHD occurrence. In Sweden, CHD risk has been markedly lower than in Finland from where a large migration occurred in the 1970s.

OBJECTIVES

To study the structural and functional markers of subclinical atherosclerosis in twin pairs discordant for migration with the main focus on age at migration, length of residence and integration into Swedish society after migration from a high to a lower CHD risk country.

METHODS

Carotid intima-media thickness (IMT) and brachial artery endothelial function (EF) were assessed with high-resolution ultrasound and a set of cardiovascular, socio-economic and psychosocial risk factors were estimated in 76 middle-aged male twin pairs discordant for migration from Finland to Sweden.

RESULTS

Men who had migrated in adolescence had lower IMT values compared with their co-twins living in Finland (0.665 +/- 0.114 vs. 0.802 +/- 0.167 mm, P = 0.009). Also men who integrated well to Swedish society had lower (0.720 +/- 0.154 vs. 0.799 +/- 0.207 mm, P = 0.013) IMT values than their twin brothers living in Finland. Associations between IMT and migration age and between IMT and integration remained significant in multivariate analyses of several CHD risk factors. The intrapair difference in IMT was significantly associated with immigration age and integration (ANOVA, P = 0.0082), the difference being greatest among pairs where the brother living in Sweden had migrated at early age and integrated well to Swedish society. EF was better in men who had migrated to Sweden before the age of 21 years, but not later, compared with their co-twins in Finland (6.4 +/- 4.6% vs. 3.8 +/- 3.6%, P = 0.025).

CONCLUSIONS

Migration at an early age and good integration are beneficial to vascular health associated with moving from a high to a lower CHD risk country, suggesting that an environment-sensitive period influences atherogenesis before adulthood.

Migration and coronary heart disease: A study of Finnish twins living in Sweden and their co-twins residing in Finland

BACKGROUND

Finland and Sweden are neighbouring countries with a substantially higher incidence and mortality from coronary heart disease (CHD) in Finland. Migration from Finland to Sweden has resulted in a population of about 187,000 Finnish immigrants, with a higher risk of CHD than Swedes. The aim of the present study was to analyse the prevalence of CHD in migrants to Sweden compared with co-twins remaining in Finland.

METHODS

The study population consisted of twin pairs of the Finnish Twin Cohort Study where at least one twin had lived one year or more in Sweden, including 1,534 subjects and 251 complete twin pairs discordant regarding residency in Sweden. Emigrant twins were compared with nonmigrant co-twins regarding prevalence of CHD in 1998. CHD prevalence was assessed by self-reported questionnaires validated using information from a clinical examination.

RESULTS

Self-reported CHD showed a good correspondence with clinical diagnosis. Differences in social and behavioural risk factors for CHD among men were small but emigrants were more physically active than non-migrants. Female emigrants had less overweight and better education, but were more often working class than non-migrants. Intra-pair comparisons restricted to migration discordant pairs showed a tendency towards a reduced prevalence of CHD in the migrant co-twins (0.6; 0.3-1.4). In analyses of all subjects disregarding pair status, emigrants showed a reduced prevalence of CHD compared with subjects always living in Finland (0.6; 0.4-0.9).

CONCLUSION

Emigration from Finland to Sweden may be associated with a reduced prevalence of CHD. The causes are most likely multifactorial and may involve changes in dietary habits, physical activity, psychosocial factors, and inflammation.

Heritability of flow-mediated dilation: a twin study

BACKGROUND

Endothelial dysfunction assessed by brachial artery flow-mediated dilation (FMD) is a marker for early atherosclerotic vascular disease and future cardiovascular events.

OBJECTIVE

To estimate the heritability of brachial artery FMD using a twin design.

METHODS

We estimated the heritability of FMD using 94 middle-aged male twin pairs. FMD was measured by ultrasound, and traditional coronary heart disease risk factors were measured. Genetic modeling techniques were used to determine the relative contributions of genes and environment to the variation in FMD.

RESULTS

The mean age of the twin participants was 54.9 +/- 2.8 years. The mean FMD was 0.047 +/- 0.030. The intraclass correlation coefficient was higher in MZ twins [0.38, 95% confidence interval (CI) 0.32-0.43] than in DZ twins (0.19, 95% CI 0.11-0.26), suggesting a role of genetic influence in FMD variation. Structural equation modeling showed that both genetic and unique environmental factors contributed significantly to the variation in FMD. The crude FMD heritability was 0.37 (95% CI 0.15-0.54). After adjustment for traditional cardiovascular risk factors, including age, total cholesterol, blood pressure, and body mass index, the heritability of FMD was 39% (95% CI 0.18-0.56). The remaining variation in FMD could be explained by individual-specific environment.

CONCLUSION

This is the first study using twins to estimate the relative contributions of genetics and environment to the variation in FMD in a US population. Our results demonstrate a moderate genetic effect on brachial artery FMD, independent of traditional coronary risk factors. Our data also highlight the importance of unique environment on the variability in FMD.

Migration and differences in dietary habits-a cross sectional study of Finnish twins in Sweden

OBJECTIVE

To compare dietary habits between Finnish twin migrants to Sweden and their co-twins always living in Finland, and to analyse how migration influenced food consumption patterns in the migrants.

SUBJECTS/METHODS

Same-sexed twin pairs born in Finland below 75 years of age, with at least one twin migrating to Sweden (n=1083 pairs). Dietary habits were assessed by a food frequency questionnaire included in a comprehensive mailed questionnaire (response rate 71%). For 76 male twin pairs, information was also collected by a dietary history interview inquiring the habitual diet during the previous year.

RESULTS

Migrant twins in Sweden had a lower intake of typical Finnish foods like dark bread and berries, and an increased consumption of fresh fruit compared with co-twins living in Finland. The migrants consumed less potatoes and more rice and pasta. Sweet pastries were consumed less often by the migrants and they also tended to more often cut out visible fat of meat and on the other hand add salt to dishes. Among men the migrants had a lower alcohol intake than their co-twins living in Finland.

CONCLUSIONS

Migration from Finland to Sweden is associated with differences in the food pattern that reflect population differences in eating habits between the two countries. The differences include a reduced consumption of typical Finnish foods like dark bread and berries and are of bidirectional nature from the point of view of cardiovascular health.

Heritability of carotid intima-media thickness: a twin study

OBJECTIVE

To estimate the heritability of carotid intima-media thickness (IMT), a surrogate marker for atherosclerosis, independent of traditional coronary risk factors.

METHODS AND RESULTS

We performed a classical twin study of carotid IMT using 98 middle-aged male twin pairs, 58 monozygotic (MZ) and 40 dizygotic (DZ) pairs, from the Vietnam Era Twin Registry. All twins were free of overt cardiovascular disease. Carotid IMT was measured by ultrasound. Bivariate and multivariate analyses were used to determine the association between traditional cardiovascular risk factors and carotid IMT. Intraclass correlation coefficients and genetic modeling techniques were used to determine the relative contributions of genes and environment to the variation in carotid IMT. In our sample, the mean of the maximum carotid IMT was 0.75+/-0.11. Age, systolic blood pressure and HDL were significantly associated with carotid IMT. The intraclass correlation coefficient for carotid IMT was larger in MZ (0.66; 95% confidence interval [CI], 0.62-0.69) than in DZ twins (0.37; 95% CI, 0.29-0.44), and the unadjusted heritability was 0.69 (95% CI, 0.54-0.79). After adjusting for traditional coronary risk factors, the heritability of carotid IMT was slightly reduced but still of considerable magnitude (0.59; 95% CI, 0.39-0.73).

CONCLUSION

Genetic factors have a substantial influence on the variation of carotid IMT. Most of this genetic effect occurs through pathways independent of traditional coronary risk factors.

Structural and functional changes in peripheral vasculature of Fabry patients

OBJECTIVE

Fabry disease is a lysosomal storage disorder due to deficient alpha-galactosidase A activity, which leads to glycosphingolipid accumulation especially in vascular smooth-muscle and endothelial cells. Little is known about the effects of Fabry disease on peripheral artery function and structure. Therefore, we aimed to further characterize the peripheral vascular structural and functional changes in Fabry disease.

METHODS AND RESULTS

We measured structural and functional vascular parameters, including intima-media thickness (IMT) of brachial and carotid arteries and abdominal aorta, carotid and aortic compliance, and brachial artery flow-mediated dilatation (FMD) in 17 Fabry patients and 34 healthy controls matched for age, sex and smoking. Carotid IMT (0.64 +/- 0.15 vs 0.57 +/- 0.12 mm), brachial IMT (1.02 +/- 0.25 vs 0.74 +/- 0.18 mm), and aortic IMT (0.31 +/- 0.09 vs 0.26 +/- 0.04 mm) were significantly increased, and brachial FMD was significantly impaired (6.3 +/- 5.0 vs 9.7 +/- 3.9%) in Fabry patients compared to healthy controls (p < 0.05 in all comparisons after adjustments for age, LDL-cholesterol, and systolic blood pressure). No differences were observed in arterial compliance between the groups.

CONCLUSIONS

These data suggest that Fabry disease affects arterial function and structure by disturbing peripheral endothelial function and promoting intima-media thickening.

Higher Mortality and Different Pattern of Causes of Death Among Foreign-Born Compared to Native Swedes 1970–1999

In a previous Swedish longitudinal study of mortality among 723,948 foreign born and native-born Swedes, 1970-1999, increased mortality was found among foreign-born persons. This study describes and analyses the differences in mortality between 361,974 foreign-born persons and 361,974 native Swedes during the period 1970-1999, based on data from Statistics Sweden and the National Board of Health and Welfare. The mortality pattern showed dissimilarities; with a significantly higher number of deaths among foreign-born persons in six diagnose groups and a significantly lower mean age at time of death. A high number of deaths were found for migrants from Denmark in Neoplasm, for migrants from Finland and Poland in Diseases of the circulatory system and for migrants from Yugoslavia in Symptoms, signs and ill-defined conditions. There is a tendency to a more similar pattern between foreign- and Swedish-born persons over time. Migration may be a risk factor for health, and therefore seems to be an important factor to consider when studying morbidity and health and when planning preventive work.

Genotype at the −174G/C Polymorphism of the Interleukin-6 Gene Is Associated With Common Carotid Artery Intimal-Medial Thickness

BACKGROUND AND PURPOSE

Studies in unrelated individuals have produced conflicting findings concerning the putative association between the interleukin-6 (IL-6) -174G/C polymorphism and carotid intimal-medial thickness (IMT). We have used a family-based genetic association design to assess the heritability of carotid IMT and to investigate the hypothesized association of carotid IMT with the IL-6 to -174G/C polymorphism.

METHODS

We studied 854 members of 224 white British families. The heritability of carotid IMT was determined using Multipoint Engine for Rapid Likelihood Inference. Genetic association analyses were carried out using ANOVA and family-based tests of association implemented in Quantitative Transmission Disequilibrium Test. A meta-analysis of previous studies of the association was conducted to place our result in context.

RESULTS

The heritability of carotid IMT was 24%. Under a recessive model (GG+GC versus CC), there was significant evidence of association between IL-6 to the -174G/C genotype and adjusted log(e) maximal carotid IMT (F=5.469; P=0.02). Family-based analyses using Quantitative Transmission Disequilibrium Test showed no evidence of population stratification as a cause of the observed association (chi2(1)=0.469; P=0.4934). The CC genotype was associated with a 4.8% increase in maximal carotid IMT and accounted for 0.6% of the observed variation in the trait, which is equivalent to 2.5% of the heritable component. A meta-analysis of the present and 2 previous large studies, which enrolled a total of 2930 subjects, confirmed the recessive effect of the C allele on carotid IMT (P=0.0014).

CONCLUSIONS

The genotype at the IL-6 to -174G/C polymorphism is associated with common carotid artery IMT, although the size of the genetic effect is small.

Inflammatory gene load is associated with enhanced inflammation and early carotid atherosclerosis in smokers

BACKGROUND AND PURPOSE

Smoking acts as a pro-inflammatory stimulus. Inflammation may provide a key mechanism by which smoking causes atherosclerosis. If so, then the degree to which an individual mounts an inflammatory response is likely to influence atherosclerosis severity. This study examined the impact of inflammatory gene polymorphisms and gene-smoking interactions on common carotid artery intima-media thickness (IMT), a measure of early atherosclerosis.

METHODS

In a community population (n=1000), mean IMT was determined using ultrasound. This population was genotyped for 6 polymorphisms in 4 inflammatory genes: IL-6-174, IL-6-572, and IL-6-597; IL-1-beta-31; IL-1 receptor antagonist VNTR and CD14-159. Serum IL-6 levels were measured in the first 500 subjects. Genotypes/haplotypes associated with higher IL-6 levels were designated "inflammatory haplotypes." A gene load score was calculated, in which 2 represented individuals homozygous for > or =2 inflammatory genotypes/haplotypes and 0 was homozygous for none.

RESULTS

Increasing gene load of inflammatory genotypes was associated with a linear increase in serum IL-6 levels (P=0.018) and increased carotid artery IMT (P=0.003). There was a significant interaction between gene load and smoking status on carotid IMT (P for interaction=0.002). Specifically, in smokers, carriers of inflammatory haplotypes had significantly increased age- and sex-adjusted IMT (IL-6-174C/IL-6-572G/IL-6-597A, P=0.005; IL-1-beta-31T/IL-1RN*2,P=0.04; CD14-159CC, P=0.028).

CONCLUSIONS

These findings support the hypothesis that inflammation and cytokine responses provide a key mechanism by which smoking causes atherogenesis. Secondly, they highlight the importance of gene-environment, and gene-gene-environment interactions in the pathogenesis of atherosclerosis.

Genetics of Ultrasonographic Carotid Atherosclerosis

The search for genes related to the cause of common complex disorders such as cardiovascular disease has been frustrating, partly because of the many factors known to contribute to cardiovascular disease and the potential "distance" of cardiovascular disease as a phenotype from genes and gene products. Linkage and association studies for phenotypes more proximal in the pathway from DNA sequence variation to overt clinical disease, such as ultrasound-defined carotid atherosclerosis, may potentially be more enlightening. Only one genetic variant previously reported to be associated with atherosclerosis or clinically evident cardiovascular disease, matrix metalloproteinase (MMP) 3, has shown consistently positive associations with carotid disease, although it has not been studied widely. Another, PON1 L55M, is weakly associated in subgroups only, and 2, ApoE and MTHFR, are equivocal. Genetic variants reported to be associated with clinical cardiovascular disease show weak or no relationship to carotid atherosclerosis. This may reflect the known inconsistency in associations of genetic variants with clinical cardiovascular disease itself. Alternatively, genetic determinants of ultrasound-defined carotid atherosclerosis may differ from those of clinically manifest cardiovascular disease and may require pursuit through large-scale genomic studies of carotid atherosclerosis as a distinct phenotype. Only 1 genetic variant, MMP 3, has shown consistently positive associations with ultrasonographic carotid disease, although it has not been studied widely. Another, PON1 L55 mol/L, is weakly associated in subgroups only. Genetic variants reported to be associated with clinical cardiovascular disease show weak or no relationship to carotid atherosclerosis.

Weight Reduction With Very-Low-Caloric Diet and Endothelial Function in Overweight Adults: Role of Plasma Glucose

OBJECTIVE

Obesity is associated with endothelial dysfunction that may contribute to the development of atherosclerosis. We studied whether weight reduction improves endothelial function in overweight individuals.

METHODS AND RESULTS

Flow-mediated endothelium-dependent vasodilation of the brachial artery was measured in 67 adults (age: 46+/-7 years, body mass index: 35.2+/-5.4 kg/m2) before and after a 6-week weight reduction program induced by very-low-calorie diet (daily energy: 580 kcal/2.3 MJ). Caloric restriction reduced body weight from 101+/-18 to 90+/-17 kg. Flow-mediated vasodilation increased from 5.5%+/-3.7 to 8.8%+/-3.7% (P<0.0001). Nitrate-mediated vasodilation was not significantly affected. The improvement in flow-mediated dilation was associated with the reduction in plasma glucose concentration (P=0.0003). This relationship was independent of changes in weight, serum lipids, oxidized LDL, C-reactive protein, adiponectin, blood pressure, and insulin.

CONCLUSIONS

Weight reduction with very-low-calorie diet improves flow-mediated vasodilation in obese individuals. This improvement is related to the reduction in plasma glucose concentration. These observations suggest that changes in glucose metabolism may determine endothelial vasodilatory function in obesity.

Enhanced endothelium-dependent vasodilation in subjects with Proline7 substitution in the signal peptide of neuropeptide Y

Neuropeptide Y (NPY) is a molecule that may have both vasoconstrictive and vasodilatory actions. A common polymorphism in the human NPY gene that results in the Leucine7 to Proline7 substitution (Leu7Pro) in the signal peptide part of the NPY was recently identified. This substitution has been associated with elevated serum cholesterol levels and with slightly accelerated progression rate of carotid intima-media thickness, thus suggesting increased risk of atherosclerosis in carriers of Pro7 substitution. Recent data also indicate that subjects with Pro7 substitution may have increased endothelial release of NPY. This study was undertaken to elucidate the effects of Leu7Pro polymorphism on arterial endothelial function. We measured flow-mediated endothelial-dependent dilatation (FMD) of the brachial artery in two separate populations: in 152 middle-aged men and in 95 prepubertal children. In both study populations, subjects with Pro7 substitution had 48-52% higher FMD compared with subjects having the wildtype (Leu7/Leu7) signal peptide sequence. We conclude that Pro7 substitution in signal peptide of the NPY is associated with enhanced endothelial-dependent vasodilation. Prospective studies are needed to determine whether Pro7 substitution is associated with increased or decreased risk of cardiovascular morbidity and mortality.

Interleukin-6 promoter polymorphism modulates the effects of heavy alcohol consumption on early carotid artery atherosclerosis: the Carotid Atherosclerosis Progression Study (CAPS)

BACKGROUND AND PURPOSE

A J-shaped relationship has been demonstrated between alcohol and both clinical cardiovascular events and carotid atherosclerosis. A similar J-shaped relationship has been found between alcohol intake and inflammatory markers. If inflammation were on the intermediate causal pathway between alcohol intake and atherosclerosis, then genetic determinants of enhanced inflammation would be expected to modify this relationship.

METHODS

In a large community population (n=1000; age, 50 to 65 years), we studied the effects of the interleukin-6 (IL-6)-174 polymorphism and gene-alcohol interactions on common carotid artery intima-media thickness (CCA-IMT) and carotid plaque.

RESULTS

The CC genotype was associated with significantly higher IL-6 levels; the odds ratio (OR) for IL-6 in the top quartile was 2.07 (95% CI, 1.16 to 3.72; P=0.014). Interactions were seen between genotype and alcohol consumption for both IL-6 levels and CCA-IMT. In individuals who drank >30 g/d of alcohol, the CC genotype was associated with higher IL-6 levels, elevated CCA-IMT (P=0.001), and increased risk of carotid plaque (OR, 3.64; 95% CI, 1.15 to 11.54; P=0.028). The J-shaped relationship between alcohol intake and IMT was seen only for the CC genotype.

CONCLUSIONS

These data suggest that the IL-6-174 promotor polymorphism may modulate the effects of alcohol on carotid atherosclerosis. These data support the hypothesis that inflammation forms part of the intermediate causal pathway between alcohol intake and atherosclerosis.

Early carotid atherosclerosis and family history of vascular disease: specific effects on arterial sites have implications for genetic studies

OBJECTIVE

Carotid artery intima-media thickness (IMT) is an intermediate phenotype for atherosclerosis. In a community population (n=5400), we determined whether a parental history of myocardial infarction (MI) or stroke is associated with increased IMT and whether associations differ at specific sites in the carotid arterial tree.

METHODS AND RESULTS

Using regression modeling, the proportion of IMT that remains unexplained after controlling for vascular risk factors was determined. A parental history of stroke was associated with both increased common carotid artery (CCA) and increased internal carotid artery (ICA)-IMT, but in young individuals (<or=60 years of age), the association was stronger with ICA-IMT, with an odds ratio (95% CI) for ICA-IMT in the highest quartile of 2.31 (1.67 to 3.21), P<0.001, compared with 1.53 (1.07 to 2.20), P=0.019, for CCA-IMT. In contrast, a parental history of MI was associated with increased CCA-IMT both overall and in young individuals but not with ICA-IMT, with an odds ratio (95% CI) for increased CCA-IMT of 2.51 (1.94 to 3.25), P<0.001, compared with 1.03 (0.78 to 1.35), P=0.861, for ICA-IMT.

CONCLUSIONS

IMT has a significant familial component that is independent of conventional risk factors. Associations for stroke and MI differ at specific sites in the carotid arterial tree. Although commonly used aggregate CCA/ICA-IMT measures may be appropriate for candidate gene studies investigating stroke risk, these results suggest that CCA-IMT alone may be a better marker for MI risk.