Circulation Topic Review

Transcription

1 Circulation Topic Review Genetic Epidemiology in Circulation and the Circulation Subspecialty Journals The Editors The following articles are being highlighted as part of Circulation s Topic Review series. This series will summarize the most important manuscripts, as selected by the editors, published in Circulation and the Circulation subspecialty journals. The studies included in this article represent the articles related to genetic epidemiology that were published in Circulation and its subspecialty journals in 2010 and (Circulation. 2012;125:e443-e455.) Separating the Mechanism-Based and Off-Target Actions of Cholesteryl Ester Transfer Protein Inhibitors With CETP Gene Polymorphisms Summary: The inverse relationship between high-density lipoprotein cholesterol and risk of coronary heart disease suggests that therapeutic elevation of high-density lipoprotein cholesterol may provide an effective means of prevention of coronary heart disease. Pharmacological inhibition of cholesteryl ester transfer protein (CETP) leads to elevation in high-density lipoprotein cholesterol, but torcetrapib (the first-in-class CETP inhibitor) increased the risk of cardiovascular events in the ILLUMINATE trial (Investigation of Lipid Level Management to Understand Its Impact in Atherosclerotic Events), which may have resulted from an unexpected blood pressure elevating effect of this agent. We used common genetic polymorphisms in the CETP gene to distinguish whether the hypertensive action of torcetrapib was mechanism based or off target, because a genetic study of these variants can be considered to be a type of natural randomized trial of a clean low-dose CETP inhibitor with no off-target actions. Common CETP gene polymorphisms and torcetrapib treatment had concordant effects on 8 lipid and lipoprotein markers, including high-density lipoprotein cholesterol, but CETP gene variants had no effect on blood pressure. The blood pressure elevating effect of torcetrapib appears to be an off-target action that is unlikely to be shared by chemically dissimilar CETP inhibitors. Genetic studies could be used in drug-development programs as a new source of randomized evidence for drug-target validation in humans. Conclusions: Discordance in the effects of CETP single-nucleotide polymorphisms and torcetrapib treatment on blood pressure despite the concordant effects on lipids indicates the hypertensive action of torcetrapib is unlikely to be due to CETP inhibition or shared by chemically dissimilar CETP inhibitors. Genetic studies could find a place in drug-development programs as a new source of randomized evidence for drug-target validation in humans. 1 Comprehensive Analysis of Genomic Variation in the LPA Locus and Its Relationship to Plasma Lipoprotein(a) in South Asians, Chinese, and European Caucasians Summary: Increased cardiovascular disease risk has been associated with plasma lipoprotein(a) [Lp(a)] levels, though somewhat inconsistently, limiting implementation in common clinical practice. Circulating concentrations of Lp(a) are largely under the control of genetic variation in the LPA gene due to the cumulative effects of multiple rare and common genetic variants. A common copy number variation in LPA, created by a variable number of exons coding for kringle IV type 2 domains, is known to affect Lp(a) concentration but, until recently, has not been measurable in cohorts with limited quantities of genomic DNA available. We demonstrate that a correlation exists between single-nucleotide polymorphisms in the LPA locus and kringle IV type 2 copy number and that both LPA single-nucleotide polymorphisms and kringle IV type 2 copy number contribute to Lp(a) concentration and, thus, should be measured in future studies of Lp(a). In agreement with previous work, the relationship between genomic variation in LPA and Lp(a) concentration appears to vary among ethnicities. Additional genetic variants that are too rare, have effects too small to be detected in the SHARE sample, or were not queried in this study, play a greater role in South Asians and Chinese. Further identification of rare and common variants is required in these and other ethnicities. Finally, our work shows that future Mendelian randomization studies investigating Lp(a) would benefit from including both LPA single-nucleotide polymorphisms and kringle IV type 2 copy number, as the extent of Lp(a) concentration explained is larger using both types of variation. Conclusions: LPA single-nucleotide polymorphisms are in linkage disequilibrium with kringle IV type 2 copy number, but kringle IV type 2 copy number explains an increment in plasma Lp(a) variation over single-nucleotide polymorphisms alone. Thus, both single-nucleotide polymorphisms and kringle IV type 2 copy number should be included in future genetic epidemiology studies of Lp(a). 2 Novel Associations of Multiple Genetic Loci With Plasma Levels of Factor VII, Factor VIII, and Von Willebrand Factor: The CHARGE (Cohorts for Heart and Aging Research in Genome Epidemiology) Consortium Summary: Elevated circulating levels of coagulation factor VIII (FVIII) and von Willebrand factor (vwf) are risk factors for venous thrombosis, but the data supporting an association of coagulation factor VII (FVII) levels with arterial thrombosis are less consistent. Hemorrhagic complications are associated with deficiency in FVII and vwf (von Willebrand disease), as well as X-linked deficiency in FVIII (hemophilia A). To date, our understanding of genetic variation influencing plasma levels has been focused primarily on variation in the genes encoding each protein product (F7, F8, and VWF, respectively). Using data from adults drawn from Correspondence to The Editors, Circulation Editorial Office, 560 Harrison Avenue, Suite 502, Boston, MA, circ@circulationjournal.org 2012 American Heart Association, Inc. Circulation is available at DOI: /CIRCULATIONAHA e443

2 e444 Circulation March 13, 2012 community populations, we investigated genome-wide associations between common genetic variation and plasma levels of FVII, FVIII, and vwf. For FVII, we identified 5 loci on 5 chromosomes that exceeded genome-wide significance. All loci were within or near genes, including 4 new candidate genes and F7. For vwf, we identified 8 loci on 6 chromosomes. All loci were within genes, including 6 new candidate genes, as well as ABO and VWF. For FVIII, 5 loci were identified and overlapped vwf findings. We replicated 9 of the 10 new findings in independent samples. In summary, new genetic associations were discovered in biological pathways not previously associated with circulating levels of these factors, including proteins implicated in uptake and intracellular transport of the factors. These findings may point to novel prevention and treatment targets of hemostasis disorders. Conclusions: New genetic associations were discovered outside previously known biological pathways and may point to novel prevention and treatment targets of hemostasis disorders. 3 Risk of Recurrent Venous Thrombosis in Homozygous Carriers and Double Heterozygous Carriers of Factor V Leiden and Prothrombin G20210A Summary: Homozygous or double heterozygous factor V Leiden and/or prothrombin G20210A is a rare inherited thrombophilic trait. Although individuals who have these mutations are at an 20-fold increased risk of first venous thrombosis, it is uncertain whether the risk of recurrence in these individuals is also increased. The clinical implications for such individuals, such as receiving anticoagulant treatment for an indefinite time after first venous thrombosis, depend on the risk of recurrence. In this case-control study, performed in a large cohort of thrombophilic families, we assessed the risk of recurrence of venous thrombosis in individuals with homozygosity or double heterozygosity for factor V Leiden and prothrombin G20210A. The cohort consisted of 788 individuals with prior venous thrombosis, of whom 325 had recurrent events. A total of 494 mutations were identified. Compared with noncarriers, carriers of the mutations factor V Leiden (n 283), prothrombin G20210A (n 82), double heterozygous (n 49) or homozygous factor V Leiden, or homozygous prothrombin G20210A (n 27) did not display an increased risk of recurrent events. Testing for these genetic mutations in patients with first venous thrombosis seems therefore to be of limited use. Conclusions: In this study, individuals with homozygous factor V Leiden and/or homozygous prothrombin G20210A or double heterozygous carriers of factor V Leiden and prothrombin G20210A did not have a high risk of recurrent venous thrombosis. 4 Clinical and Genetic Correlates of Circulating Angiopoietin-2 and Soluble Tie-2 in the Community Summary: Experimental studies suggest that endothelial growth factors play an important role in angiogenesis and vascular remodeling. We evaluated the clinical and genetic correlates of circulating angiopoietin-2 (Ang-2) and its soluble receptor/regulator Tie-2 (stie-2) in a community-based sample. Ang-2 levels were higher and stie-2 levels were lower in women than in men. Ang-2 was positively related to age, smoking, systolic blood pressure, hypertension treatment, and diabetes, whereas stie-2 was positively associated with body mass index, diabetes, and triglycerides. Circulating Ang-2 and stie-2 were higher in participants with the metabolic syndrome, with stronger associations of Ang-2 with blood pressure traits and of stie-2 with obesity-dyslipidemia components. Heritability estimates for Ang-2 and stie-2 were 27% and 56%, respectively. A region on chromosome 9 was significantly linked to circulating stie-2 levels (log of the odds score, 8.31). These observations are consistent with the concept that angiogenesis and vascular remodeling are influenced by genetic factors and associated with metabolic risk factors. Conclusion: Circulating levels of Ang-2 and stie-2 are heritable traits associated with cardiovascular disease risk factors, including the metabolic syndrome. These observations are consistent with the notion that angiogenesis and vascular remodeling are determined in part by genetic influences and associated with metabolic risk factors. 5 Genomic Variation Associated With Mortality Among Adults of European and African Ancestry With Heart Failure: The Cohorts for Heart and Aging Research in Genomic Epidemiology Consortium Summary: This study investigated 2526 incident heart failure (HF) cases of European ancestry and 466 incident HF cases of African ancestry for an association between genome-wide variation and all-cause mortality. One variant in the CKLF-like MARVEL transmembrane domain containing 7 (CMTM7) genes was significantly associated with all-cause mortality in individuals of European ancestry with HF. CMTM7 is 1 of several chemokine-like factor genes clustered in the same region on chromosome 3p22. These results suggest that chemokines may play a role in survival of patients with HF. No genomic variation was significantly associated with mortality in individuals with HF of African ancestry. Future studies of this type may identify genes that lead to an improved understanding of HF pathophysiology and treatment of the disease. These findings warrant additional investigation, including replication, in other studies of HF. Conclusions: This study identified a novel locus associated with all-cause mortality among individuals of European ancestry with HF. This finding warrants additional investigation, including replication, in other studies of HF. 6 Candidate Gene Association Resource (CARe): Design, Methods, and Proof of Concept Summary: The National Heart, Lung, and Blood Institute s Candidate Gene Association Resource (CARe), a planned cross-cohort analysis of genetic variation in cardiovascular, pulmonary, hematologic, and sleep-related traits, comprises more than participants representing 4 ethnic groups in 9 community-based cohorts. The CARe study is anticipated to provide many new insights into the relationship of genetics and various clinical traits and diseases. Conclusions: The CARe Pilot Study validates the operational framework for phenotype collection, single-nucleotide polymorphism genotyping, and analytic pipeline of the CARe project and validates the planned candidate gene study of approximately 2000 biological candidate loci in all participants and genome-wide association study in approximately 8000 African American participants. CARe will serve as a valuable resource for the scientific community. 7 Differences in Albuminuria Between Hispanics and Whites: An Evaluation by Genetic Ancestry and Country of Origin: The Multi-Ethnic Study of Atherosclerosis Summary: We investigated whether Hispanic subgroups (identified by country of origin) differ in both genetic component and risk for albumin in the urine, which is an important risk factor for cardiovascular events and kidney disease. We observed that Hispanics differ in their genetic ancestral component by country of origin. In addition, their risk of albuminuria differs by country of origin when compared with whites. Our findings suggest that country of origin

3 The Editors Genetic Epidemiology e445 should be included as a covariate when studying differences between Hispanics and non-hispanic whites for select cardiovascular risk factors. Conclusions: Hispanics are a heterogeneous group with varying genetic ancestry. Risks of albuminuria differ across the country of origin groups. These differences may be due, in part, to differences in genetic ancestral components. 8 Association of Genome-Wide Variation With the Risk of Incident Heart Failure in Adults of European and African Ancestry: A Prospective Meta-Analysis From the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium Summary: Genetic factors contribute to heart failure (HF) onset and, to date, most approaches to identify genetic variants associated with HF risk have relied on candidate genes. No large-scale genome-wide investigation of HF risk has been published. We investigated the association of 2.5 million single-nucleotide polymorphisms with incident HF by meta-analyzing data from 4 community-based prospective cohorts: the Atherosclerosis Risk in Communities Study, the Cardiovascular Health Study, the Framingham Heart Study, and the Rotterdam Study. Among European-ancestry participants with 2526 incident HF events, we identified 1 locus with a singlenucleotide polymorphism, whose probability value ( )exceeded the genome-wide statistical significance threshold of and was associated with a 53% increase in HF risk. Among 2895 African-ancestry participants who had 466 incident events, we identified 1 locus with a single-nucleotide polymorphism, whose probability value ( ) exceeded the genome-wide statistical significance and was associated with a 46% increase in HF risk. We identified an additional 14 loci in European-ancestry and Africanancestry participants that were marked by high-signal single-nucleotide polymorphisms with a probability value For most loci, risk estimates were modest and did not seem to differ in subjects without a myocardial infarction preceding HF onset. Our results suggest that there may be several genomic regions associated with new-onset HF in older adults, and support the hypothesis that common genetic variation, regardless of the clinical mechanism responsible for reduced cardiac output in HF, contributes to the risk. These findings merit replication in other community-based settings of incident HF. Conclusions: We identified 2 loci that were associated with incident HF and exceeded genome-wide significance. The findings merit replication in other community-based settings of incident HF. 9 Mediterranean Dietary Pattern Is Associated With Improved Cardiac Autonomic Function Among Middle-Aged Men: A Twin Study Summary: The Mediterranean diet is associated with lower cardiovascular risk. Lower heart rate variability, reflecting cardiac autonomic dysfunction, is a risk factor for cardiac death. To date, no prior studies have explored the association between a whole diet conforming to the Mediterranean diet and cardiac autonomic function measured as heart rate variability. Using a twin study design, for the first time, to our knowledge, we found that the more an individual s diet conformed to the Mediterranean diet, the greater the heart rate variability, indicating better cardiac autonomic function. This positive association was independent of genes, shared environmental factors, and known cardiovascular risk factors; this means that whether or not a person has an adverse genetic background or other risk factors for cardiovascular disease, this person would be likely to have better cardiac autonomic function if he or she follows a diet similar to the Mediterranean diet. Conclusions: The Mediterranean dietary pattern is associated with higher heart rate variability. 10 Relation of Platelet and Leukocyte Inflammatory Transcripts to Body Mass Index in the Framingham Heart Study Summary: There have been many genetic epidemiology and biomarker studies examining associations of common genetic variants (DNA) and circulating proteins with clinically apparent cardiovascular disease and associated risk factors; however, there has been relatively little study of gene expression or transcriptomics. Quantitative differences in the abundance of transcripts (messenger RNA) has been demonstrated in specific malignancies, but gene expression from a large community-based cohort examining cardiovascular disease or its risk factors has never been reported. In this study, we measured quantitative expression of 48 genes in 1846 participants of the Framingham Offspring cohort from RNA derived from isolated platelets and leukocytes. Specific inflammatory platelet-derived transcripts were significantly associated with higher body mass index. Compared with platelets, fewer leukocyte-derived transcripts were associated with body mass index or other cardiovascular risk factors. Select transcripts were found to be highly heritable. This study demonstrates that inflammatory transcripts derived from platelets, particularly those part inflammatory regulating pathways, are associated with BMI, whereas other distinct transcripts, many known to be related to platelet function, are heritable. This is the first study, using a large community-based cohort, to demonstrate that quantitative gene expression is associated with risk factors, most notably body mass index. Conclusions: Inflammatory transcripts derived from platelets, particularly those part of the nuclear factor kappa B pathway, are associated with BMI, whereas others are heritable. This is the first study, using a large community-based cohort, to demonstrate clinical correlates of gene expression and is consistent with the hypothesis that specific peripheral-blood transcripts play a role in the pathogenesis of coronary heart disease and its risk factors. 11 Fine-Mapping in African Americans of 8 Recently Discovered Genetic Loci for Plasma Lipids: The Jackson Heart Study Summary: A principal goal of genetic association studies has been to augment current disease prediction algorithms by identifying genetic variants associated with common diseases. Genome-wide association (GWA) studies have identified many novel loci associated with plasma lipid traits. However, most GWA studies published to date have been conducted exclusively in samples of European ancestry. Therefore, it is unclear whether these loci are relevant in a broader range of ethnic groups such as African Americans. Results from GWA studies direct interest to regions of association in the genome, but, typically, the causal variants remain unknown. Many have postulated that densely genotyping these regions in African Americans may lead to identification of the causal variant because of the unique genetic architecture on the African ancestral background. In the current study, we tested polymorphisms from loci identified through GWA and fine-mapped regions in the Jackson Heart Study, a community-based cohort of African American individuals in Jackson, Miss. Our study addresses whether the same genetic loci identified in populations of European ancestry through GWA will be associated with blood lipids and, therefore, possibly predictive in African Americans. We also demonstrate the advantages and disadvantages of using a fine-mapping approach in African Americans to identify causal variants within the associated genomic regions. Conclusions: We confirm that 5 genetic regions associated with lipid traits in European-derived populations are relevant in African Amer-

4 e446 Circulation March 13, 2012 icans. To further evaluate these loci, fine-mapping in larger African American cohorts and/or resequencing will be required. 12 Genetic Determinants of Major Blood Lipids in Pakistanis Compared With Europeans Summary: Levels of the major blood lipids, LDL-C, HDL-C, and triglyceride are each strongly associated with the risk of coronary heart disease (CHD). Several genetic variants have been established in the regulation of lipid metabolism in people of European continental ancestry; however there are few data available on the genetic determinants of these lipid traits in South Asians a population with a high burden of cardiometabolic conditions. We investigated variants across 2000 genes in 3200 Pakistanis, and 2450 Germans using the same gene array. A total of 41 variants at 14 loci, were found to be significantly associated with major lipid traits in Pakistanis, explaining 6.2%, 7.1%, and 0.9% of the variation in HDL-C, triglyceride, and LDL-C, respectively. The most significant lipid-related variants identified among Pakistanis corresponded to genes previously shown to be relevant to Europeans, such as CETP associated with HDL-C levels; APOA5/ZNF259 and GCKR with triglyceride levels; and CELSR2 variants with LDL-C levels. However, differing allelic frequencies and lipid effects for variants in APOA5 were observed in Pakistanis compared with Europeans. This study suggests that several lipid-related genetic variants are common to Pakistanis and Europeans, though they explain only a modest portion of population variation in lipid concentration. Allelic frequencies and the effect sizes of lipid-related variants can differ between Pakistanis and Europeans. Conclusions: Several lipid-related genetic variants are common to Pakistanis and Europeans, though they explain only a modest proportion of population variation in lipid concentration. Allelic frequencies and effect sizes of lipid-related variants can differ between Pakistanis and Europeans. 13 Independent Susceptibility Markers for Atrial Fibrillation on Chromosome 4q25 Summary: Atrial fibrillation (AF) is a heritable disorder with evidence of genetic susceptibility. Common single-nucleotide polymorphisms (SNPs) in a noncoding region on chromosome 4q25 have been associated with AF. We sought to determine whether more than 1 AF susceptibility signal exists at this locus. We genotyped SNPs at the chromosome 4q25 locus in 790 case subjects and 1177 control subjects. After adjustment for the genotype of the most significantly associated SNP, the SNPs that remained significantly associated with AF were replicated in an additional 5066 subjects with AF and without AF. We identified 3 distinct AF susceptibility signals, 2 of which have not been described previously. A multimarker risk score composed of SNPs tagging each of these 3 AF susceptibility signals identified individuals at varying risk of developing AF. Among the 1% of subjects homozygous for AF risk alleles at SNPs tagging each susceptibility signal, the risk of AF was markedly increased relative to those with the most common genotypes at these SNPs (relative risk 6.02, 95% confidence interval , P ). Consideration of multiple susceptibility signals at the chromosome 4q25 locus identifies individuals with a markedly increased risk of AF and may facilitate the localization of regulatory elements at this locus with particular biological relevance in the pathogenesis of AF. Conclusions: We identified 2 novel AF susceptibility signals on chromosome 4q25. Consideration of multiple susceptibility signals at chromosome 4q25 identifies individuals with an increased risk of AF and may localize regulatory elements at the locus with biological relevance in the pathogenesis of AF. 14 Design of the Coronary Artery Disease Genome-Wide Replication and Meta-Analysis (CARDIoGRAM) Study: A Genome-Wide Association Meta-Analysis Involving More Than Cases and Controls Summary: Despite the recent progress in identification of coronary artery disease (CAD)/myocardial infarction genes, only a relatively limited fraction ( 10%) of the overall genetic risk (heritability) of the disease is explained by the currently identified loci. One part of the explanation is likely to be the limited power of individual genome-wide association studies to detect such loci. The global Coronary ARtery DIsease Genome-Wide Replication And Metaanalysis (CARDIoGRAM) consortium will now analyze genomewide information from cases of CAD and controls, and this will undoubtedly identify additional loci harboring common variants affecting CAD risk. Indeed, we anticipate a wealth of new information on heritable aspects of CAD and its risk factors, which likely will open multiple opportunities for scientific exploration. However, such a large experiment requires careful prospective planning of the methodology used. Here we describe how such a meta-analysis, including a replication study, could be conducted. InConclusion, CARDIoGRAM is a novel and powerful consortium poised to contribute to the understanding of common genetic variation affecting the risk for CAD and myocardial infarction. This information then can be used to derive mechanistic information on biological processes as well as used to identify potential targets for therapeutic intervention. Conclusion: CARDIoGRAM is poised to contribute to our understanding of the role of common genetic variation on risk for CAD and myocardial infarction. 15 Genome-Wide Linkage and Positional Candidate Gene Study of Blood Pressure Response to Dietary Potassium Intervention: The Genetic Epidemiology Network of Salt Sensitivity Study Summary: Current understanding of the genetic mechanisms underlying blood pressure (BP) response to dietary potassium intake is limited. Using data from 3142 Han Chinese participants, including 1906 who took part in a 7-day high-sodium diet followed by a 7-day high-sodium plus potassium dietary intervention, we conducted a genome-wide linkage scan and positional candidate gene study of systolic BP, diastolic BP, and mean arterial pressure responses to changes in dietary potassium intake. Our results identified regions on chromosomes 3 and 11 that may harbor important susceptibility loci for dietary potassium sensitivity. In addition, a novel variant in the angiotensin II receptor, type 1, gene was shown to be a strong predictor of BP response to dietary potassium. These findings provide early evidence of a definitive genetic mechanism underlying potassium sensitivity. Elucidating the genetic mechanisms that influence this complex phenotype could provide further insight into the pathophysiology of hypertension. In addition, cataloging variants that influence this trait could potentially lead to the development of targeted dietary interventions among potassium-sensitive subgroups for the primary and the secondary prevention of hypertension. Conclusions: Genetic regions on chromosomes 3 and 11 may harbor important susceptibility loci for potassium sensitivity. Furthermore, the AGTR1 gene was a significant predictor of BP responses to potassium intake. 16 Multiple Genetic Loci Influence Serum Urate Levels and Their Relationship With Gout and Cardiovascular Disease Risk Factors Summary: Although the role of serum urate in the causal pathway for gout has been well characterized, substantial controversy exists

5 The Editors Genetic Epidemiology e447 regarding whether elevated serum urate also may be a cause of high blood pressure (BP), hyperglycemia, and chronic kidney disease; whether the association with serum urate observed in observational studies merely is a consequence of these conditions; or whether it is an artifact of uncontrolled confounding factors. Because the association between genes and disease generally is not subject to confounding by environmental factors or reverse causality, causal inferences between exposure and disease can be examined more specifically using Mendelian randomization. In the present investigation, we tested the association of a genetic score constructed using 8 loci associated with serum urate with coronary heart disease (CHD) and its risk factors, including gout, glucose, systolic BP, diastolic BP, estimated glomerular filtration rate, and chronic kidney disease. Except for gout, none of the associations was statistically significant, and the lack of associations was replicated in another equally large independent sample. Although further confirmation is warranted, our study helps to elucidate the relationship between serum urate and CHD and its risk factors, which may contribute to a better understanding of the usefulness of controlling serum urate for preventing and designing treatments for CHD and its risk factors. Conclusions: The genetic urate score analysis suggested a causal relationship between serum urate and gout but did not provide evidence for one between serum urate and cardiovascular risk factors and CHD. 17 Determinants of Blood Pressure in Preschool Children: The Role of Parental Smoking Summary: There is increasing evidence that environmental tobacco exposure has significant effects on cardiovascular health even at a young age. Abnormal arterial morphology and function have been demonstrated in teenagers exposed to second-hand smoking. The age at which cardiovascular effects of passive smoking first become detectable has not been established to date. This population-based study was designed to explore endogenous and exogenous determinants of blood pressure (BP) in preschool children. BP was measured in conjunction with a family health and lifestyle survey in a cohort of 4236 children aged 4 to 6 years. Multifactorial dependency of BP on body stature and familial, prenatal, and environmental influences was observed. Among these factors, exposure to parental smoking was associated with a small but consistent BP-raising effect, which remained significant when adjusted for numerous potentially collinear anthropometric, medical, and social factors affecting BP in the children and their parents, including prenatal conditions. Childhood BP was quantitatively correlated with the daily cigarette consumption of the mothers only, compatible with closer exposure to maternal smoking at home. The findings of this study add an important pediatric perspective to the issue of prevention and containment of active and passive smoking. They complete the picture of tobacco exposure interfering with cardiovascular maturation and health from gestation to adulthood. The benefit of successful primary prevention programs would most likely not be limited to adults but extend even to the youngest family members. Conclusions: In healthy preschool children, parental smoking is an independent risk factor for higher blood pressure, adding to other familial and environmental risk factors. Implementing smoke-free environments at home and in public places may provide a long-term cardiovascular benefit even to young children. 18 Lipoprotein(a) Genetic Variants Associated With Coronary and Peripheral Vascular Disease But Not With Stroke Risk in the Heart Protection Study Summary: Recent genetic studies have demonstrated strong support for a causal role of plasma levels of lipoprotein(a) [Lp(a)] in coronary disease. The current findings from the Heart Protection Study, which are based on prevalent disease cases and 3000 incident events, increase our understanding of the relevance of Lp(a) for vascular disease risk. The Heart Protection Study demonstrates comparable strength of associations of an LPA genotype score, previously shown to explain more than half of the genetic variation in Lp(a) levels with coronary disease and peripheral vascular disease but not with stroke. These results indicate that Lp(a) may have effects on atherosclerotic and thrombotic diseases that are only relevant at specific sites. Furthermore, as indicated by the paradoxical results from prospective and randomized evidence for cholesterol and ischemic stroke risk, the lack of evidence of an association of LPA and stroke in the present study does not exclude the possibility that lowering Lp(a) could have beneficial effects on the risk of stroke or stroke subtypes. The results of large-scale randomized trials of agents that reduce plasma levels of Lp(a), such as niacin and cholesterylester transfer protein inhibitors, will help to assess the safety and efficacy of lowering Lp(a) levels on a broad range of vascular outcomes. Conclusions: The comparable strength of associations of the LPA score with coronary disease and peripheral vascular disease but not with stroke suggest that lipoprotein(a) may have effects on atherothrombotic vascular disease that are only relevant at specific sites. 19 Heterogeneity of the Phenotypic Definition of Coronary Artery Disease and Its Impact on Genetic Association Studies Summary: There have been many genetic epidemiology and biomarker studies examining associations of common genetic variants (DNA) and circulating proteins with clinically apparent cardiovascular disease and associated risk factors; however, there has been relatively little study of gene expression or transcriptomics. Quantitative differences in the abundance of transcripts (messenger RNA) has been demonstrated in specific malignancies, but gene expression from a large community-based cohort examining cardiovascular disease or its risk factors has never been reported. In this study, we measured quantitative expression of 48 genes in 1846 participants of the Framingham Offspring cohort from RNA derived from isolated platelets and leukocytes. Specific inflammatory platelet-derived transcripts were significantly associated with higher body mass index. Compared with platelets, fewer leukocyte-derived transcripts were associated with body mass index or other cardiovascular risk factors. Select transcripts were found to be highly heritable. This study demonstrates that inflammatory transcripts derived from platelets, particularly those part inflammatory regulating pathways, are associated with BMI, whereas other distinct transcripts, many known to be related to platelet function, are heritable. This is the first study, using a large community-based cohort, to demonstrate that quantitative gene expression is associated with risk factors, most notably body mass index. Conclusions: Substantial phenotypic heterogeneity exists in coronary artery disease genetic associations, but differences in phenotype definition make a small contribution to between-study heterogeneity. We did not find a consistent effect in terms of the magnitude or homogeneity of summary effects for a specific phenotype to support its preferential use in genetic studies or meta-analyses for coronary artery disease. 20 Genetic Risk Score and Risk of Myocardial Infarction in Hispanics Summary: Coronary heart disease disproportionately affects certain ethnic groups. Hispanics are affected by excessive rates of cardiovascular risk factors such as diabetes mellitus, overweight and obesity, dyslipidemia, and hypertension. This study evaluated whether genetic markers identified from genome-wide association studies in whites were associated with myocardial infarction (MI) in Hispanics. We determined 14 variations in 1989 cases with a first nonfatal acute MI and 2096 population-based controls. Our results indicated that 7 single-nucleotide polymorphisms at 3 independent

6 e448 Circulation March 13, 2012 loci were associated with MI risk. A genetic risk score summing the number of the associated risk alleles was also associated with MI, per unit related to 18% (11% to 25%) increased risk. The improvement in genetic markers on discrimination of MI, represented by the area under the receiver-operating characteristic curve, was modest but significant. Our findings highlight the importance of examining ethnic differences in genetic susceptibility to MI and indicate that consideration of multiple susceptibility signals may identify individuals with a markedly increased risk of MI. Conclusions: These results indicate both the consistency and disparity of genetic effects on risk of MI between Hispanic and white populations. The improvement in the identified genetic markers on discrimination of MI in Hispanics was modest. 21 The Effect of Survival Bias on Case-Control Genetic Association Studies of Highly Lethal Diseases Summary: Genetic association studies seek to establish links between specific genetic variants and phenotypes such as quantifiable traits or disease states. These studies use the same recruitment formats and are subject to many of the same types of bias that can invalidate the results of standard epidemiological studies. Survival bias, the phenomenon by which individuals are excluded from analysis of a trait because they die as a result of the trait s expression, has been suggested as a potential explanation for the lack of case-control replication of results obtained using longitudinal cohorts. A genetic variant that increases risk of both incidence and mortality of a disease could be found in a longitudinal cohort but could remain undetected in case-controls because individuals with that variant die before study recruitment. We modeled 3 cardiovascular diseases of high lethality: myocardial infarction, acute ischemic stroke, and intracerebral hemorrhage, using existing data from population-based studies. We simulated genetic variants that modify baseline risk for both incidence and mortality from these diseases and constructed longitudinal and case-control studies to test the observed associations between our genetic variants and disease incidence. Our results suggest that the erosion of effect size caused by survival bias is small and is calculable using formulas we provide. Furthermore, study designs that can ensure 40% recruitment of lethal cases can lessen the percentage of effect size erosion caused by survival bias. These results should help genetic researchers compare the results of genetic studies using differing recruitment frameworks. Conclusions: Our simulation provides formulas to allow estimation of effect size erosion given a variant s odds ratio of disease, odds ratio of lethality, and minor allele frequencies. These formulas will add precision to power calculation and replication efforts for case-control genetic studies. Our approach requires validation using prospective data. 22 SCN5A Variation Is Associated With Electrocardiographic Traits in the Jackson Heart Study Summary: Normal electric activity of the heart (measured by the ECG traits P, PR, QRS, QT, and QTc durations; heart rate; and P, QRS, and T axes) is determined in part by both rare and common genetic variation. Previous studies of the candidate gene SCN5A, which encodes the Na v 1.5 voltage-gated sodium channel, have identified mutations responsible for cardiac conduction disease, the long-qt syndrome, the Brugada syndrome, and other lifethreatening arrhythmias. Common SCN5A variation has also been implicated in contributing to the variation observed in ECG traits, particularly in African-descent populations, in which the nonsynonymous SCN5A rs (S1103Y) is rare or monomorphic in other populations. To further characterize the association of common SCN5A variation with normal ECG traits in populations of African descent, we undertook a SCN5A candidate gene association study for ECG traits in 3000 blacks ascertained as part of the Jackson Heart Study. A total of 13 independent associations were identified for the 9 ECG traits tested adjusting for age, sex, and European ancestry. Of these associations, most were novel and not previously reported in the literature. Overall, the effect size for each associated genetic variant on any one ECG trait was small, explaining up to 2% of the trait variability in this population. Although SCN5A common genetic variation is associated with normal electric activity of the heart, the impact probably is small and leaves much of heritability unexplained. Conclusions: These results suggest that SCN5A variation contributes to ECG trait distributions in blacks, and these same variations may be risk or protective factors associated with susceptibility to arrhythmias. 23 Genetic Predictors of Fibrin D-Dimer Levels in Healthy Adults Summary: Activation of blood coagulation plays a key role in hemostasis and in arterial and venous thrombosis. Fibrin D-dimer is the most widely used clinical marker of activated blood coagulation. Epidemiological and clinical studies over the last 20 years have established its associations with risk of arterial and venous thromboembolic events and with other pathologies. This article reports a novel association of plasma D-dimer levels with variation upstream from F3, the gene for tissue factor. The manuscript also confirms a previous report that D-dimer levels are associated with the factor V Leiden F5 R506Q variant (rs6025) and the FGA Ala331Thr variant (rs6050) variant, which are also associated with risk of arterial and venous thrombosis. Our demonstration that a genetic variant upstream from F3 is associated with variation in D-dimer levels in generally healthy populations supports the concept that F3 might be a potential therapeutic target to reduce thrombotic risk. Conclusions: Three genes were associated with fibrin D-dimer levels. Of these 3, the F3 association was the strongest, and has not been previously reported. 24 Ethnic Differences in Out-of-Hospital Fatal Pulmonary Embolism Summary: This report presents the first epidemiological study involving a large number of autopsy-based out-of-hospital fatal pulmonary embolism investigations in New York City, with its diverse ethnic population. New data presented should alert and aid clinicians in evaluating patients at risk for acute and fatal pulmonary embolism on the basis of different ethnic backgrounds. Because blacks and Hispanics suffer fatal pulmonary embolism at a significantly younger age than whites, physicians should closely monitor these populations for known risk factors (such as body mass index) and counsel healthy lifestyles, especially at younger ages. Because of the large number of prothrombin G2010A carriers observed in white and Hispanic out-of-hospital pulmonary embolism decedents, testing for prothrombin G20210A in high-risk patients is indicated. Finally, our results clearly point to the need for additional research to identify other genetic causes of fatal pulmonary embolism, especially in blacks, who have low frequencies of known genetic risk factors. Conclusion: There are unique epidemiological differences in out-ofhospital fatal pulmonary embolism between ethnic groups in New York City. 25 Common Genetic Variants, QT Interval, and Sudden Cardiac Death in a Finnish Population-Based Study Summary: There are more than sudden cardiac deaths (SCDs) annually in the United States. Although there are known genetic syndromes that account for high sudden death risk in individuals, these account for only a small proportion of all sudden

7 The Editors Genetic Epidemiology e449 deaths. The current study sought to identify common genetic variants that contribute to SCD risk in the general population. The authors created a list of candidate variants that are known to be associated with electrocardiographic QT interval (an intermediate phenotype for SCD) and calculated a QT genotype score, based on the QT interval effect per allele copy number, summed over all variants. They validated the robust association between these variants in aggregate and the continuous QT interval (P ) as well as the individual per-snp effects, and replicated the relationship between the QT interval itself and SCD risk. There was no evidence, however, for a linear relationship between the QT genotype score and SCD risk. In exploratory secondary analyses, there was a suggestion of increased risk at the highest QT genotype score. In its current form, the QT genotype score was not a predictor of SCD risk, although power to detect such an effect was limited for SCD, a complex trait with heterogeneous contributing causes. As the number of known common variants is expanded, further testing for the ability to improve SCD risk prediction will be necessary. Conclusions: Our study strongly replicates the relationship between common genetic variants and the QT interval and confirms the relationship between the QT interval and SCD but does not show evidence for a linear relationship between QT(score) and SCD risk. 26 Genetic and Clinical Correlates of Early-Outgrowth Colony-Forming Units Summary: Cells termed endothelial progenitor cells (EPCs) have attracted interest as potential biomarkers and even cellular therapies for cardiovascular disease. This enthusiasm stems from studies suggesting that lower EPC number is associated with increased risk of cardiovascular disease and events and the hypothesis that EPCs, broadly defined, contribute to endothelial repair. However, this literature encompasses several different phenotypic definitions of EPCs and small to medium-sized patient samples. In the present study, we measured a specific EPC phenotype, early-outgrowth colony-forming units (CFUs), in 1799 participants of the Framingham Heart Study. Among individuals without cardiovascular disease, CFUs showed significant inverse associations with the Framingham Risk Score, advanced age, female sex, and triglycerides; positive associations were found with hormone replacement and statin therapy. In a genome-wide association study, polymorphisms were significantly associated with CFUs at the MOSC1 and the SLC22A3-LPAL2-LPA loci; SLC22A3-LPAL2-LPA is a previously replicated susceptibility locus for myocardial infarction. Alleles at the SLC22A3-LPAL2-LPA locus that were associated with decreased CFUs were also highly related to increased risk of myocardial infarction. These data support the hypothesis that decreased CFU number promotes susceptibility to myocardial infarction in a community sample and warrant independent replication and further mechanistic studies. Conclusions: In a community-based sample, early-outgrowth CFUs are inversely associated with select cardiovascular risk factors. Furthermore, genetic variants at the SLC22A3-LPAL2-LPA locus are associated with both decreased CFUs and an increased risk of myocardial infarction. These findings are consistent with the hypothesis that decreased circulating angiogenic cell populations promote susceptibility to myocardial infarction. 27 Relative Familial Clustering of Cerebral Versus Coronary Ischemic Events Summary: Although differences in heritability of cerebrovascular and coronary artery disease may improve risk prediction, future genetic studies, and understanding of disease mechanisms, the relative heritability of acute cerebral and coronary events has rarely been studied, In a prospective, population-based study, the family history of myocardial infarction (MI) and stroke in first-degree relatives was compared between patients presenting with acute coronary syndromes and patients presenting with transient ischemic attacks and stroke. Nine hundred six patients with acute coronary syndromes and 1015 with transient ischemic attacks and stroke were compared. Although parental MI and stroke were common in both patient populations, there was greater clustering of MI than of stroke within families. Patients with acute coronary syndromes were 5 times more likely than patients with strokes or transient ischemic attacks to have 2 or more siblings with disease in the same arterial territory, despite similar overall incidence of MI and stroke in our study population. Moreover, the relative heritability of MI was greater than stroke because parental MI predicted sibling MI, whereas parental stroke did not predict sibling stroke. The use of composite measures of family history of vascular disease in risk scores and in screening may not be optimal because the heritability of stroke is much less than that of MI. Genome-wide scanning is unlikely to identify causative gene loci for stroke, given the finding of substantially greater heritability of MI versus stroke and the relatively small number of major loci discovered in relation to MI to date. Conclusions: Heritability of coronary events was greater than that of cerebral events, such that MI was more likely to cluster in families than was stroke. 28 Genome-Wide Significance and Replication of the Chromosome 12p11.22 Locus Near the PTHLH Gene for Peripartum Cardiomyopathy Summary: Peripartum cardiomyopathy (PPCM) is an uncommon diagnosis but is often devastating for those it affects: younger women who are in their childbearing years. Although evidence is sparse, risk factors for PPCM and its more heterogeneous relative, pregnancyassociated cardiomyopathy, may include maternal age 30 years, multiparity, multiple gestation, a history of preeclampsia, use of tocolytics, and African ancestry. Heritable factors may also influence PPCM, and this study reports the discovery and validation of a novel PPCM locus on chromosome 12. Although not located within a classic gene, the implicated single nucleotide polymorphism is near the parathyroid hormone like hormone gene, which is an excellent candidate gene for PPCM. This discovery may signal important directions for pathophysiologic research of PPCM etiology, while also providing a fertile bed for further genetic association studies of this and other possible causal sequence variants in the genomic region. Additional studies are warranted to evaluate potential clinical applications of these observations. Conclusions: Genome-wide association with PPCM was discovered and replicated for rs at chromosome 12p11.22 near PTHLH. This study indicates a role of genetic factors in PPCM and provides a new locus for further pathophysiological and clinical investigation. 29 A Genome-Wide Association Study Identifies LIPA as a Susceptibility Gene for Coronary Artery Disease Summary: In relation to polygenic coronary artery disease, recent genome-wide association studies have revealed interesting novel loci whose pathophysiological significance is incompletely understood at present. Variation in gene expression may be an important intermediate link between common genetic variants and phenotypes. In our study, combining information from genome-wide association studies and global gene expression in peripheral blood monocytes, a cell type central to the atherosclerotic process, we identified interesting single-nucleotide polymorphisms in the LIPA (lysosomal acid lipase A) gene on chromosome 10q23 in relation to coronary artery disease. LIPA gene expression was also associated with endothelial function, an intermediate phenotype of coronary artery disease. Consistent associations at the genetic, gene expression, subclinical disease, and disease levels support a causal relationship and add a pathophysiologically plausible candidate for future investigation in cardiovascu-