Common Variant on Chromosome 9p21 Predicts Severity of Coronary Artery Disease

Genetics of coronary artery disease - a clinician's perspective

Coronary artery disease (CAD) is the major cause of fatality and disability among all cardiovascular diseases (CVD). Intricate interactions of genes and environment dictate the outcomes of CAD. Technological advances in the different fields of genetics including linkage studies (LS), candidate gene studies (CGS) and genome-wide association studies (GWA studies) have augmented the knowledge of pathogenesis of CAD. LS were more successful in identifying genetic variants among monogenic disease. GWA studies were relatively popular in identification of variation in polygenic disease. Until now, GWA studies recognized about 50 loci determining around 6% of the heritability in CAD. Clinical utility of the above knowledge would result in better CAD management, but validation of the variants in native population is warranted for active adoption into the clinic. The major aim of this review is to provide an adequate perspective of our current understanding and advances of genetics in CAD.

Role of 9p21 and 2q36 variants and arterial stiffness in the prediction of coronary artery disease

BACKGROUND

Genetic polymorphisms and arterial stiffness indices have been associated with cardiovascular prognosis and the presence and extent of angiographic coronary artery disease (CAD). We aimed to investigate whether arterial stiffness indices and 9p21 and 2q36 variants may improve prediction of CAD presence and extent when added to classical cardiovascular risk factors in patients at high risk for CAD.

MATERIALS AND METHODS

In this cross-sectional study, we enrolled 183 consecutive patients with suspected stable CAD (age 61 ± 9 years, 134 males) referred for diagnostic coronary angiography. Framingham risk score (FRS) was calculated. Arterial stiffness was assessed by carotid-femoral pulse wave velocity (PWV) and central augmentation index (AIx) using applanation tonometry. Genetic polymorphisms of 9p21 (rs1333049) and 2q36 (rs2943634) loci were also analysed.

RESULTS

Higher FRS and PWV and the presence of rs2943634 risk allele were independent predictors of CAD (Nagelkerke R(2) 0·252, P < 0·001), while higher FRS and the presence of rs1333049 risk allele were independent predictors of multivessel CAD (Nagelkerke R(2) 0·190, P < 0·001). Genetic polymorphisms and vascular indices did not improve the predictive accuracy of FRS-based models (P > 0·1 for all) for CAD presence or extent.

CONCLUSIONS

In these high-risk patients, 9p21 and 2q36 variants and PWV were independently associated with CAD presence and extent, but the addition of both genetic data and arterial stiffness indices to FRS did not improve the prediction of CAD compared with FRS alone. Further studies are needed to clarify the prognostic role of genetic and vascular indices in the prediction of angiographic CAD.

The association of 9p21-3 locus with coronary atherosclerosis: a systematic review and meta-analysis

BACKGROUND

Studies suggest that the 9p21-3 locus may influence susceptibility to myocardial infarction. We performed a systematic review and meta-analysis to assess whether this locus is associated with severity of coronary atherosclerosis and adverse clinical outcomes in those with known coronary disease.

METHODS

Multiple electronic databases were searched from inception through August 2012. Studies examining 9p21-3 genotype in patients with known coronary artery disease were included. We extracted the association of the 9p21-3 locus with measures of severity of coronary atherosclerosis [number of diseased vessels, Gensini Score, Duke CAD Prognostic Index (DPI)], angiographic outcomes [change in minimum lumen diameter (∆MLD) and number of new lesions at follow-up], and key clinical outcomes (all-cause mortality, recurrent myocardial infarction and the need for coronary revascularization). Relative risks (RR) and weighted mean difference (WMD) were pooled using the random effects models.

RESULTS

23 cohorts enrolling 16,860 participants were analyzed. There was no significant difference between HR and LR genotypes in terms of all-cause mortality, recurrent myocardial infarction or the frequency of coronary revascularization. HR genotype was associated with increased risk of triple vessel disease (RR = 1.34; 95% CI 1.08-1.65; P = 0.01) and increased baseline Gensini Score (WMD = 5.30; 95% CI 0.66-9.93; P = 0.03). However there was no association with DPI (WMD = 4.00; 95% CI 2.94-10.94; P = 0.26). HR genotype did not predict ∆MLD or number of new lesions at follow-up.

CONCLUSIONS

Patients of coronary atherosclerosis who carry the high risk genotype of the 9p21-3 allele may be more likely to have multi-vessel CAD. However the effect of this allele on CAD progression and disease specific clinical outcomes are not observed possibly due to diminishing genetic risk following dietary modification and therapy.

Evaluation of association between common genetic variants on chromosome 9p21 and coronary artery disease in Turkish population

Objective:

Coronary artery disease (CAD), which develops from complex interactions between genetic and enviromental factors, is a leading cause of death worldwide. Based on genome-wide association studies (GWAS), the chromosomal region 9p21 has been identified as the most relevant locus presenting a strong association with CAD in different populations. The aim of the present study was to investigate the association of two SNPs on chromosome 9p21 on susceptibility to CAD and the effect of these SNPs along with cardiovascular risk factors on the severity of CAD in the Turkish population.

Methods:

This study had an observational case-control design. We genotyped 460 subjects, aged 30-65 years, to investigate the association of 2 SNPs (rs1333049, rs2383207) on chromosome 9p21 and CAD risk in Turkish population. Real-time polymerase chain reaction (RT-PCR) was used to analyze the 2 SNPs in CAD patients and healthy controls. The genotype and allelic variations of these SNPs with the severity of CAD was also assessed using semi-quantitative methods such as the Gensini score. Student’s t test and multiple regression analysis were used for statistical analysis.

Results:

The SNPs rs1333049 and rs2383207 were found to be associated with CAD with an adjusted OR of 1.81 (95% Cl 1.05-3.12) and 2.12 (95% CI 1.19-4.10) respectively. After adjustment of CAD risk factors such as smoking, family history of CAD and diabetes, the homozygous AA genotype for rs2383207 increased the CAD risk with an OR 3.69. Also a very strong association was found between rs1333049 and rs2383207 and Gensini scores representing the severity of CAD (p<0.001).

Conclusion:

The rs2383207 and rs1333049 SNPs on 9p21 chromosome were significantly associated with the risk and severity of CAD in the Turkish population.

Genetic variants at chromosome 9p21 and risk of first versus subsequent coronary heart disease events: a systematic review and meta-analysis

Objectives

The purpose of this analysis was to compare the association between variants at the chromosome 9p21 locus (Ch9p21) and risk of first versus subsequent coronary heart disease (CHD) events through systematic review and meta-analysis.

Background

Ch9p21 is a recognized risk factor for a first CHD event. However, its association with risk of subsequent events in patients with established CHD is less clear.

Methods

We searched PubMed and EMBASE for prospective studies reporting association of Ch9p21 with incident CHD events and extracted information on cohort type (individuals without prior CHD or individuals with established CHD) and effect estimates for risk of events.

Results

We identified 31 cohorts reporting on 193,372 individuals. Among the 16 cohorts of individuals without prior CHD (n = 168,209), there were 15,664 first CHD events. Ch9p21 was associated with a pooled hazard ratio (HR) of a first event of 1.19 (95% confidence interval: 1.17 to 1.22) per risk allele. In individuals with established CHD (n = 25,163), there were 4,436 subsequent events providing >99% and 91% power to detect a per-allele HR of 1.19 or 1.10, respectively. The pooled HR for subsequent events was 1.01 (95% confidence interval: 0.97 to 1.06) per risk allele. There was strong evidence of heterogeneity between the effect estimates for first and subsequent events (p value for heterogeneity = 5.6 × 10⁻¹¹). We found no evidence for biases to account for these findings.

Conclusions

Ch9p21 shows differential association with risk of first versus subsequent CHD events. This has implications for genetic risk prediction in patients with established CHD and for mechanistic understanding of how Ch9p21 influences risk of CHD.

Association between the chromosome 9p21 locus and angiographic coronary artery disease burden: a collaborative meta-analysis

OBJECTIVES

This study sought to ascertain the relationship of 9p21 locus with: 1) angiographic coronary artery disease (CAD) burden; and 2) myocardial infarction (MI) in individuals with underlying CAD.

BACKGROUND

Chromosome 9p21 variants have been robustly associated with coronary heart disease, but questions remain on the mechanism of risk, specifically whether the locus contributes to coronary atheroma burden or plaque instability.

METHODS

We established a collaboration of 21 studies consisting of 33,673 subjects with information on both CAD (clinical or angiographic) and MI status along with 9p21 genotype. Tabular data are provided for each cohort on the presence and burden of angiographic CAD, MI cases with underlying CAD, and the diabetic status of all subjects.

RESULTS

We first confirmed an association between 9p21 and CAD with angiographically defined cases and control subjects (pooled odds ratio [OR]: 1.31, 95% confidence interval [CI]: 1.20 to 1.43). Among subjects with angiographic CAD (n = 20,987), random-effects model identified an association with multivessel CAD, compared with those with single-vessel disease (OR: 1.10, 95% CI: 1.04 to 1.17)/copy of risk allele). Genotypic models showed an OR of 1.15, 95% CI: 1.04 to 1.26 for heterozygous carrier and OR: 1.23, 95% CI: 1.08 to 1.39 for homozygous carrier. Finally, there was no significant association between 9p21 and prevalent MI when both cases (n = 17,791) and control subjects (n = 15,882) had underlying CAD (OR: 0.99, 95% CI: 0.95 to 1.03)/risk allele.

CONCLUSIONS

The 9p21 locus shows convincing association with greater burden of CAD but not with MI in the presence of underlying CAD. This adds further weight to the hypothesis that 9p21 locus primarily mediates an atherosclerotic phenotype.

Interferon-γ activates expression of p15 and p16 regardless of 9p21.3 coronary artery disease risk genotype

OBJECTIVES

Because post-transcriptional mechanisms modulate levels of p16 (encoded by CDKN2A) and p15 (encoded by CDKN2B), we tested whether interferon-γ regulates the expression of these proteins and the effect of the 9p21 genotype.

BACKGROUND

The mechanism whereby the common variant at chromosome 9p21.3 confers risk for coronary artery disease (CAD) remains uncertain. A recent report proposed that 9p21.3 confers differential activation of adjacent genes in response to interferon-γ, and reported that mRNA levels of CDKN2B are reduced in response to interferon-γ.

METHODS

Human umbilical vein endothelial cells (HUVECs), aortic smooth muscle cells, HeLa cells, HEK293 cells, and 16 human lymphoblastoid cell lines, all genotyped for the 9p21.3 locus, were treated with interferon-γ and analyzed by immunoblot.

RESULTS

In all cells tested--except HUVECs where expression was not modulated by interferon-γ--regardless of 9p21.3 genotype, interferon-γ increased the expression of p16 and p15. Northern blot analysis confirmed that interferon-γ has little effect on mRNA levels of CDKN2A and CDKN2B.

CONCLUSIONS

The 9p21.3 risk genotype does not affect the activation of cyclin-dependent kinase inhibitors p15 and p16 by interferon-γ. Thus, another mechanism is likely to account for the CAD risk associated with this locus.

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.