Genomics in coronary artery disease: Past, present and future

Developmental Origins of Cardiovascular Disease: Understanding High Mortality Rates in the American South

While many social scientists view heart disease as the outcome of current conditions, this cannot fully explain the significant geographic disparities in cardiovascular disease (CVD) mortality rates in the USA. The developmental origins hypothesis proposes that CVD vulnerability is created by poor conditions in utero that underbuilds major organs relative to those needed to process lush nutrition later in life. The American South underwent an economic transformation from persistent poverty to rapid economic growth in the post-World War II era. We use state-level data on income growth and current conditions to explain variation in CVD mortality rates in 2010–2011. Our proxy for unbalanced physical growth, the ratio of median household income in 1980 to that in 1950, has a large systematic influence on CVD mortality, an impact that increases dramatically with age. The income ratio combined with smoking, obesity, healthcare access, and education explain more than 70% of the variance in CVD mortality rates.

A Journey through Genetic Architecture and Predisposition of Coronary Artery Disease

Introduction

To halt the spread of coronary artery disease (CAD), the number one killer in the world, requires primary prevention. Fifty percent of all Americans are expected to experience a cardiac event; the challenge is identifying those at risk. 40 to 60% of predisposition to CAD is genetic. The first genetic risk variant, 9p21, was discovered in 2007. Genome-Wide Association Studies has since discovered hundreds of genetic risk variants. The genetic burden for CAD can be expressed as a single number, Genetic Risk Score (GRS). Assessment of GRS to risk stratify for CAD was superior to conventional risk factors in several large clinical trials assessing statin therapy, and more recently in a population of nearly 500,000 (UK Biobank). Studies were performed based on prospective genetic risk stratification for CAD. These studies showed that a favorable lifestyle was associated with a 46% reduction in cardiac events and programmed exercise, a 50% reduction in cardiac events. Genetic risk score is superior to conventional risk factors, and is markedly attenuated by lifestyle changes and drug therapy. Genetic risk can be determined at birth or any time thereafter.

Conclusion

Utilizing the GRS to risk stratify young, asymptomatic individuals could provide a paradigm shift in the primary prevention of CAD and significantly halt its spread.

A Breakthrough in Genetics and its Relevance to Prevention of Coronary Artery Disease in LMIC

More than 60 genetic risk variants predisposing to coronary artery disease (CAD) have been confirmed. The genetic risk for CAD is related to the number of genetic risk variants present and can be expressed as a genetic risk score (GRS), by summing the product of the number of high-risk variants inherited by each individual times the log of the odds ratio. Studies show risk stratification for CAD, based on the GRS, is more discriminatory than conventional risk factors and predicts the response to statin therapy. A prospective trial showed individuals with high GRS had 91% greater risk of cardiac events, and individuals with a healthy lifestyle had 46% fewer cardiac events than an unfavorable lifestyle. GRS remains the same throughout one's lifetime because your deoxyribonucleic acid does not change. GRS, determined as early as birth from saliva, is inexpensive and could transform the prevention of CAD in low- and middle-income countries.

Genetics of coronary artery disease: an update

In 2007, the first genetic risk variant, 9p21, was simultaneously discovered by two independent groups. 9p21 increases the risk of coronary artery disease in individuals with premature heart disease by twofold, and in the overall population the heterozygote is associated with a 25% increased risk and the homozygote with a 50% increased risk. It is of note that the risk mediated by 9p21 is independent of known risk factors. Since then, with the development of new technologies and the international consortium of CARDIoGRAM, there is now a total of 50 genetic risk variants confirmed and replicated for CAD. Of these 50, 35 mediate their risk by unknown mechanisms, indicating that the pathogenesis of atherosclerosis and myocardial infarction is due to additional factors as yet unknown. The role of genetic risk factors in the management of CAD is yet to be determined. Since many of them are independent of known risk factors, the genetic risk will in the future have to be incorporated into the guidelines, which recommend the target level of plasma LDL-C to be achieved based on the number of risk factors.

The role of genetic risk factors in coronary artery disease

Genome-wide association studies for coronary artery disease utilizing the case control association study approach has identified 50 genetic risk variants associated with coronary artery disease or myocardial infarction. All of these genetic variants are of genome wide significance and replicated in an independent population. It is of note that 35 of these 50 genetic risk variants act through mechanisms as yet unknown. These findings have great implications for the pathogenesis of atherosclerosis, as well as new targets for the development of novel therapies for the prevention and treatment of CAD. The genetic variant PCSK9 has already led to the development of a monoclonal anti-body which is undergoing assessment in phases I, II, and III clinical trials. This therapy shows very promising results and since it increases removal of LDL-C, it is complementary to current statin therapy. Assessing the beneficial or deleterious effects of a lifelong exposure to a genetic risk variant (Mendelian randomization) will be an important adjunct to clinical trials.

A genetic polymorphism in RBP4 is associated with coronary artery disease

Insulin resistance and obesity is influenced by the retinol binding protein 4 (RBP4) adipokine. This study aims to determine if genetic polymorphisms in RBP4 are associated with the risk of coronary artery disease (CAD) in Chinese patients. RBP4 polymorphisms were analyzed by high resolution melting (HRM) analysis in a case-control study of 392 unrelated CAD patients and 368 controls from China. The Gensini score was used to determine the severity of CAD. The genotypic and allelic frequencies of RBP4 single-nucleotide polymorphisms were evaluated for associations with CAD and severity of disease. The A allele frequency was significantly higher in CAD case groups compared to control groups (16.7% vs. 8.8%) at the RBP4 rs7094671 locus. Compared to the G allele, this allele was associated with a higher risk of CAD (OR = 2.07 (1.50–2.84)). Polymorphisms at rs7094671 were found to associate with CAD using either a dominant or recessive model (OR, 95% CI: 1.97, 1.38–2.81; 3.81, 1.53–9.51, respectively). Adjusting for sex, history of smoking, serum TC, TG, LDL-c, and HDL-c, the risk of CAD for carriers remained significantly higher in both dominant and recessive models (OR, 95% CI: 1.68, 1.12–2.51; 2.74, 1.00–7.52, respectively). However, this SNP was not significantly associated with severity of CAD using angiographic scores in multivariable linear regression models (p = 0.373). The RBP4 rs7094671 SNP is associated with CAD; however, our results do not indicate that this locus is associated with clinical severity of CAD or the extent of coronary lesions.

A genetic basis for coronary artery disease

CAD and cancer account for over one-half of all deaths in the world. It is claimed that the 21st century is the last century for CAD. This is, in part, because CAD is preventable based on randomized, placebo-controlled clinical trials, which show modifying known risk factors such as cholesterol is associated consistently with 40-60% reduction in morbidity and mortality from CAD. Comprehensive prevention will require modifying genetic risk factors that are claimed to account for 40-60% of predisposition to CAD. The 21st century is meeting this challenge with over 50 genetic risk variants discovered and replicated in large genome-wide association studies involving over 200,000 cases and controls. Similarly, 157 genetic variants have been discovered that regulate plasma lipids including, LDL-C, HDL-C, triglycerides, and total cholesterol. A major finding from these studies is that only 15 of the 50 genetic variants for CAD act through known risk factors. Hence, the pathogenesis of CAD in addition to cholesterol and other known risk factors is due to various other factors, many of which remain unknown. Secondly, genes regulating the plasma triglyceride levels are strongly associated with the pathogenesis of CAD. Thirdly, Mendelian randomization studies show no protection from genes that increase plasma HDL cholesterol. This is contrary to current opinion. These genetic risk variants have provided new targets for the development of novel therapies to prevent CAD. Already a new and potent drug has been developed targeting PCSK9, which is in phase 3 clinical trials and shows great efficacy and safety for prevention of CAD. The 21st century is looking very bright for the prevention of CAD.

Associations of platelet-activating factor acetylhydrolase (PAF-AH) gene polymorphisms with circulating PAF-AH levels and risk of coronary heart disease or blood stasis syndrome in the Chinese Han population

The circulating level of platelet-activating factor acetylhydrolase (PAF-AH) is a novel biomarker to predict the presence of coronary heart disease. PAF-AH gene polymorphisms may be responsible for the variance of circulating PAF-AH levels in individuals. However, the association of PAF-AH gene polymorphisms with circulating PAF-AH levels and the susceptibility to coronary heart disease (CHD) remains unsolved. Blood stasis syndrome (BSS) of CHD is the most common type of TCM syndromes, and a previous study discovered its relationship with the elevated circulating PAF-AH levels. However, the association of gene polymorphisms and CHD with BSS is unclear at present. In this study, four polymorphisms (R92H, I198T, A379V, V279F) of the PAF-AH gene were genotyped in 570 CHD patients, of which 299 had BSS. In addition, 317 unaffected individuals from the same hospitals served as controls. Plasma PAF-AH levels were measured in 155 controls and 271 CHD patients selected randomly, including 139 CHD patients with BSS. In the Chinese Han population, plasma PAF-AH levels in CHD patients with BSS or without BSS were significantly higher (12.9 ± 6.5 and 11.1 ± 5.0 μM, respectively) than in controls (9.3 ± 5.2 μM); this difference still remained significant after adjustment for traditional risk factors or the inflammatory factors. The R92H polymorphism was highly related to the plasma PAF-AH levels and the risk of CHD, especially among patients with BSS, even with the adjustment for the effects of traditional factors. The I198T polymorphism was highly associated with risk of CHD with BSS, but was associated with neither the risk of CHD with no BSS nor with elevated plasma PAF-AH levels.

Genes and coronary artery disease: where are we?

Susceptibility to coronary artery disease (CAD) is claimed to be 40% to 60% inherited, but until recently genetic risk factors predisposing to CAD have been elusive. Comprehensive prevention of CAD requires manipulation of genetic risk. The availability of microarrays of single-nucleotide polymorphisms enabling genome-wide association studies (GWAS) led to the discovery of 33 genetic risk variants for CAD. Surprisingly, 23 risk variants mediate their risk through unknown mechanisms, with only 10 associating with hypertension or lipids. Thus, there are several mechanisms contributing to the pathogenesis of CAD yet to be elucidated. The first risk variant discovered by GWAS was 9p21.3, which occurs in 75% of all populations except African, with a mean increased risk of 25% per copy. Of the 33 variants for CAD, the increased risk varies from 6% to 92% with a mean increased risk of 18%, occurring on average in 47% of the population. The maximum number of risk alleles per individual would be 66. In the CARDIoGRAM (Coronary Artery Disease Genome-wide Replication and Meta Analysis) study of 23 variants, the average per individual was 17, the minimum 7, and the maximum 37. The top 10th percentile has an odds ratio of 1.88 and the lowest percentile an odds ratio of 0.55. Routine genetic screening is unlikely until management is improved by genetic testing. Risk variants should provide pathophysiological insights and targets for novel therapy. While risk variants are less potent predictors of CAD, compared with biomarkers, they have the advantage of not changing in one's lifetime and are unaffected by diet, sex, age, or medication.

Clinical utility of novel biomarkers for cardiovascular disease risk stratification

Over the past few decades, a number of coronary artery disease (CAD) and cardiovascular disease (CVD) risk factors have been identified. The predictive power of "conventional" risk factors have been validated by observational, prospective and intervention studies. Nevertheless, all attempts to exactly predict the individual risk for CAD have failed, biased by a large number of incorrectly risk-classified subjects. To improve cardiovascular (CV) risk prediction, a large number of genetic and/or non-genetic biomarkers have been discovered and tested against the "classical" risk factors for their power to predict CV risk. Only few of them had a significant improvement over the predictive models. In this paper, the most investigated biomarkers will be discussed and the evidence of their use as predictors of CV will be questioned.

Association of SNP rs6903956 on chromosome 6p24.1 with angiographical characteristics of coronary atherosclerosis in a Chinese population

Objective

To explore the association between rs6903956 and severity of coronary artery disease (CAD) in a Chinese population.

Methods

A cohort of 1075 consecutive patients who underwent coronary arteriography for suspected or known coronary atherosclerosis was enrolled in our study. Coronary atherosclerosis severity was defined by Gensini's Score System and counts of diseased vessels.

Results

Gensini score frequencies and counts of diseased vessels differed among GG, AG, AA genotype groups at the rs6903956 locus (p = 0.025 for Gensini score frequencies vs. p = 0.024 for counts of diseased vessels, respectively). A univariate logistic regression analysis revealed that the genotype distribution of this SNP was associated significantly with angiographical characteristics of coronary atherosclerosis risk (p = 0.030, odds ratio (OR) = 1.444, 95% confidence interval (CI) = 1.036∼2.013 for AG vs. GG; p = 0.021, OR = 5.896, 95% CI = 1.299∼26.750 for AA vs. GG and p = 0.007, OR = 1.564, 95% CI = 1.132∼2.162 for combined (AG+AA) vs. GG). A multivariate logistic regression analysis indicated that the genotype distribution of the rs6903956 polymorphism be associated significantly with the angiographical characteristics of coronary atherosclerosis risk (p = 0.004, OR = 1.578, 95% CI = 1.155∼2.154 for GG vs. AG vs. AA; p = 0.013, OR = 1.541, 95% CI = 1.097∼2.163 for GG vs. GA+ AA). A stratification analysis revealed that male subjects and smoking subjects had a higher frequency of the rs6903956 heterozygous mutant among higher Gensini score subjects than among lower Gensini score subjects (p = 0.023, OR = 1.579, 95% CI = 1.064∼2.344 for male subgroup; p = 0.005, OR = 2.075, 95% CI = 1.249∼3.448 for smoking subgroup).

Conclusions

Allele A is a risk factor for CAD and the G-to-A allele substitution may underlie the association between rs6903956 and CAD.

Genetics of coronary artery disease in the 21st century

Coronary artery disease (CAD) is still the number-one killer in the world, and clinical trials indicate that it is preventable. Mortality and morbidity can be reduced by at least 30% to 40% by treating known risk factors. Genetic susceptibility is claimed to account for 50% of predisposition. The challenge of preventing CAD in this century, as claimed by some investigators, will require a more comprehensive prevention and treatment of environmental and genetic risk factors. Part of that challenge has been met by genome-wide association studies, which have identified 36 genetic variants with increased risk for CAD. All of these genetic variants have reached genome-wide significance (5 × 10(-8) ) and replicate in independent populations with large sample sizes. More than 50% of these variants occur in >50% of the population, with 10 occurring in >75% of the population. The challenge and the opportunity lie in the observation that >66% of these risk variants do not mediate their risk through known conventional risk factors. These results suggest that genetic predisposition for CAD is conferred by common DNA variants and many factors contributing to the pathogenesis of CAD are yet to be determined. Comprehensive prevention of CAD will most likely require combating genetic and environmental risk factors. We are on the cusp of genetic screening, and new therapeutic targets are becoming available to manage both genetic and environmental risk factors for CAD.

Association between the polymorphism of estrogen receptor α and coronary artery disease in a Chinese population

BACKGROUND

The role of estrogen receptor α (ERα) polymorphism in coronary artery disease (CAD) was investigated previously in several populations. There are few data on relation between ERa polymorphism and CAD in Chinese population. Our study was to investigate the possible association between ERα polymorphism and CAD in Chinese population.

METHODS

A total of 539 patients with CAD and 539 age and sex matched controls were examined for ERa polymorphism. DNA was obtained and ERa polymorphism was analyzed by the polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP).

RESULTS

The frequencies of the PvuII C allele were significantly higher in CAD patients than in control individuals (P<0.05). Using T allele as a reference, the odds ratio for CAD patients with C allele was 1.24 (95%CI=1.03-1.48). Using TT genotype as a reference, the odds ratio for TC genotype was 1.17 (95%CI=0.90-1.50), and for CC genotype was 1.58 (95%CI=1.05-2.38). The odds ratio for CC genotype was 1.42 (95%CI=0.94-2.15) in women and 1.72 (95%CI=1.41-2.10) in men. There were no significant differences in XbaI allele and genotype between CAD patients and control individuals.

CONCLUSIONS

The ERa PvuII polymorphism is associated with the increased risk of CAD in men of a Chinese population. Further research is needed to investigate the mechanism underlying the association between ERα polymorphism and CAD.

9p21 and the Genetic Revolution for Coronary Artery Disease

BACKGROUND

It has long been recognized that 50% of the susceptibility for coronary artery disease (CAD) is due to predisposing genetic factors. Comprehensive prevention is likely to require knowledge of these genetic factors.

CONTENT

Using a genomewide association study (GWAS), the Ottawa Heart Genomic Study and the deCODE group simultaneously identified the first genetic risk variant, at chromosome 9p21. The 9p21 variant became the first risk factor to be identified since 1964. 9p21 occurs in 75% of the population except for African Americans and is associated with a 25% increased risk for CAD with 1 copy and a 50% increased risk with 2 copies. Perhaps the most remarkable finding is that 9p21 is independent of all known risk factors, indicating there are factors contributing to the pathogenesis of CAD that are yet unknown. 9p21 in individuals with premature CAD is associated with a 2-fold increase in risk, similar to that of smoking and cholesterol. Routine genetic testing will probably remain controversial until a specific treatment is developed. Over a period of 5 years, however, GWASs have identified 30 genetic variants for CAD risk, of which only 6 act through the known risk factors.

SUMMARY

The 9p21 variant has now been established as an independent risk factor for CAD and, along with the additional 29 risk genetic variants recently identified, is likely to provide the thrust for genetic testing and personalized medicine in the near future.

Molecular biology of heart disease

Dr. Robert Roberts is currently Professor of Medicine and Director of the Ruddy Canadian Cardiovascular Genetics Centre along with being President and CEO of the University of Ottawa Heart Institute. Prior to this appointment, he was Chief of Cardiology for 23 years at Baylor College of Medicine, Houston, Texas. His original research was in cardiac enzymology which led to the development of the MBCK test which was the standard diagnostic assay for myocardial infarction for more than 3 decades. In the late 1970s, his research interests switched to molecular biology and the genetics of cardiomyopathies. He is regarded as one of the founders of molecular cardiology and has identified and sequenced more than 20 genes responsible for cardiovascular disorders. In the past 6 years, he has pursued genome-wide association studies to identify genes predisposing to coronary artery disease (CAD) and myocardial infarction. The first genetic variant for CAD, 9p21, was identified by Dr. Robert's laboratory and, in collaboration with the international consortium, CARDIoGRAM, has identified 13 novel genes for CAD.

CADgene: a comprehensive database for coronary artery disease genes

Coronary artery disease (CAD) is a complex, multifactorial disease and a leading cause of mortality world wide. Over the past decades, great efforts have been made to elucidate the underlying genetic basis of CAD and massive data have been accumulated. To integrate these data together and to provide a useful resource for researchers, we developed the CADgene, a comprehensive database for CAD genes. We manually extracted CAD-related evidence for more than 300 candidate genes for CAD from over 1300 publications of genetic studies. We classified these candidate genes into 12 functional categories based on their roles in CAD. For each gene, we extracted detailed information from related studies (e.g. the size of case–control, population, SNP, odds ratio, P-value, etc.) and made useful annotations, which include general gene information, Gene Ontology annotations, KEGG pathways, protein–protein interactions and others. Besides the statistical number of studies for each gene, CADgene also provides tools to search and show the most frequently studied candidate genes. In addition, CADgene provides cumulative data from 11 publications of CAD-related genome-wide association studies. CADgene has a user-friendly web interface with multiple browse and search functions. It is freely available at http://www.bioguo.org/CADgene/.