Genetics of Ultrasonographic Carotid Atherosclerosis

Genome-wide association study and multi-ancestry meta-analysis identify common variants associated with carotid artery intima-media thickness

Carotid artery intima-media thickness (cIMT) is a measurement of subclinical atherosclerosis that predicts future cardiovascular events, including stroke and myocardial infarction. Genome-wide association studies (GWAS) have identified only a fraction of the genetic variants associated with cIMT. We performed the largest GWAS for cIMT involving up to 131,000 individuals. For the first time, we meta-analysed a diverse range of ancestries including populations with African, Asian (Chinese), Brazilian, European, and Hispanic ancestries. Our study identified 59 independent loci (53 loci from the multi-ancestry single variant analysis of which 19 are novel, P<5x10 -8 ; 6 novel in gene-based analysis from single variant analysis, P=2.6x10 -6 , 2 novel in meta-regression) associated with cIMT. Gene-based, tissue-expression and gene-set enrichment analyses revealed novel genes of potential interest and highlighted significant relationships between vascular tissues (aorta, coronary and tibial arteries) and genetic associations. We found that circulatory levels of seven proteins, including ACAN, BCAM, DUT, ERI1, APOE, FN1, and GLRX were potentially causally associated with cIMT levels. We found a strong genome-wide correlation between cIMT and various cardiometabolic, smoking phenotypes, and lipid traits. Using Mendelian randomisation, our analyses provide robust evidence for causal associations between cIMT and several clinically relevant traits, including lipids, blood pressure, and waist circumference. Our study extends our genetic knowledge of atherosclerosis and highlights potential causal relations between risk factors, atherosclerosis and clinical diagnoses.

Extracranial carotid artery atherosclerotic plaque and APOE polymorphisms: a systematic review and meta-analysis

Introduction

Carotid atherosclerotic plaque is an important independent risk factor for stroke. Apolipoprotein E (APOE) influences cholesterol levels and certain isoforms are associated with increased carotid atherosclerosis, though the exact association between APOE and carotid plaque is uncertain. The study aimed to evaluate the association between APOE and carotid plaque.

Methods

A systematic review was performed to retrieve all studies which examined the association between carotid plaque and APOE. This study was conducted in accordance with the PRISMA guidelines. Independent readers extracted the relevant data from each study including the type of imaging assessment, plaque definition, frequency of APOE E4 carrier status and type of genotyping. Meta-analyses with an assessment of study heterogeneity and publication bias were performed. Results were presented in a forest plot and summarized using a random-effects model.

Results

After screening 838 studies, 17 studies were included for systematic review. A meta-analysis of 5 published studies showed a significant association between ε4 homozygosity and carotid plaque [odds ratio (OR), 1.53; 95% CI, 1.16, 2.02; p = .003]. Additionally, there was a significant association between patients possessing at least one ε4 allele, heterozygotes or homozygotes, and carotid plaque (OR, 1.25; 95% CI, 1.03, 1.52; p = .03). Lastly, there was no association between ε4 heterozygosity and carotid plaque (OR, 1.08; 95% CI, 0.93, 1.26; p = .30).

Conclusion

APOE ε4 allele is significantly associated with extracranial carotid atherosclerotic plaque, especially for homozygous individuals.

The Association between HDL-C and Subclinical Atherosclerosis Depends on CETP Plasma Concentration: Insights from the IMPROVE Study

The impact of cholesteryl ester transfer protein (CETP) on atherosclerosis is highly debated. This study aimed to investigate the associations between plasma CETP or CETP genotypes and carotid intima-media thickness (cIMT) and the influence of high-density lipoprotein cholesterol (HDL-C) on these associations. Plasma CETP and HDL-C concentrations were measured in 552 subjects free of any pharmacological treatment from the IMPROVE cohort, which includes 3711 European subjects at high cardiovascular risk. CETP single-nucleotide polymorphisms (SNPs) and cIMT measures (cIMT_max; cIMT_mean-max of bifurcations, common and internal carotids; plaque-free common carotid [PF CC]-IMT_mean) were available for the full cohort. In drug-free subjects, plasma CETP correlated with HDL-C levels (r = 0.19, p < 0.0001), but not with cIMT variables. When stratified according to HDL-C quartiles, CETP positively correlated with cIMT_max and cIMT_mean-max, but not with PF CC-IMT_mean, in the top HDL-C quartile only. Positive associations between the CETP concentration and cIMT_max or cIMT_mean-max were found in the top HDL-C quartile, whereas HDL-C levels were negatively correlated with cIMT_max and cIMT_mean-max when the CETP concentration was below the median (HDL-C × CETP interaction, p = 0.001 and p = 0.003 for cIMT_max and cIMT_mean-max, respectively). In the full cohort, three CETP SNPs (rs34760410, rs12920974, rs12708968) were positively associated with cIMT_max. rs12444708 exhibited a significant interaction with HDL-C levels in the prediction of cIMT_max. In conclusion, a significant interplay was found between plasma CETP and/or CETP genotype and HDL-C in the prediction of carotid plaque thickness, as indexed by cIMT_max. This suggests that the association of HDL-C with carotid atherosclerosis is CETP-dependent.

Genome-wide admixture and association study of subclinical atherosclerosis in the Women's Interagency HIV Study (WIHS)

Cardiovascular disease (CVD) is a major comorbidity among HIV-infected individuals. Common carotid artery intima-media thickness (cCIMT) is a valid and reliable subclinical measure of atherosclerosis and is known to predict CVD. We performed genome-wide association (GWA) and admixture analysis among 682 HIV-positive and 288 HIV-negative Black, non-Hispanic women from the Women's Interagency HIV study (WIHS) cohort using a combined and stratified analysis approach. We found some suggestive associations but none of the SNPs reached genome-wide statistical significance in our GWAS analysis. The top GWAS SNPs were rs2280828 in the region intergenic to mediator complex subunit 30 and exostosin glycosyltransferase 1 (MED30 | EXT1) among all women, rs2907092 in the catenin delta 2 (CTNND2) gene among HIV-positive women, and rs7529733 in the region intergenic to family with sequence similarity 5, member C and regulator of G-protein signaling 18 (FAM5C | RGS18) genes among HIV-negative women. The most significant local European ancestry associations were in the region intergenic to the zinc finger and SCAN domain containing 5D gene and NADH: ubiquinone oxidoreductase complex assembly factor 1 (ZSCAN5D | NDUF1) pseudogene on chromosome 19 among all women, in the region intergenic to vomeronasal 1 receptor 6 pseudogene and zinc finger protein 845 (VN1R6P | ZNF845) gene on chromosome 19 among HIV-positive women, and in the region intergenic to the SEC23-interacting protein and phosphatidic acid phosphatase type 2 domain containing 1A (SEC23IP | PPAPDC1A) genes located on chromosome 10 among HIV-negative women. A number of previously identified SNP associations with cCIMT were also observed and included rs2572204 in the ryanodine receptor 3 (RYR3) and an admixture region in the secretion-regulating guanine nucleotide exchange factor (SERGEF) gene. We report several SNPs and gene regions in the GWAS and admixture analysis, some of which are common across HIV-positive and HIV-negative women as demonstrated using meta-analysis, and also across the two analytic approaches (i.e., GWA and admixture). These findings suggest that local European ancestry plays an important role in genetic associations of cCIMT among black women from WIHS along with other environmental factors that are related to CVD and may also be triggered by HIV. These findings warrant confirmation in independent samples.

Update of the effect estimates for common variants associated with carotid intima media thickness within four independent samples: The Bonn IMT Family Study, the Heinz Nixdorf Recall Study, the SAPHIR Study and the Bruneck Study

Carotid intima media thickness (cIMT) is a marker for subclinical atherosclerosis. The most recent genome-wide association meta-analysis (GWAMA) from the CHARGE consortium identified four genomic regions showing either significant (ZHX2, APOC1, PINX1) or suggestive evidence (SLC17A4) for an association. Here we assess these four cIMT loci in a pooled analysis of four independent studies including 5446 individuals by providing updated unbiased effect estimates of the cIMT association signals. The pooled estimates of our four independent samples pointed in the same direction and were similar to those of the GWAMA. When updating the independent second stage replication results from the earlier CHARGE GWAMA by our estimates, effect size estimates were closer to those of the original CHARGE discovery. A fine-mapping approach within a ±50 kb region around each lead SNP from CHARGE revealed 27 variants with larger estimated effect sizes than the lead SNPs but only three of them showed a r(2) > 0.40 with these respective lead SNPs from CHARGE. Some variants are located within potential functional loci.

Polymorphisms in IL-10 and INF-γ genes are associated with early atherosclerosis in coronary but not in carotid arteries: A study of 122 autopsy cases of young adults

Atherosclerosis is a complex disease, involving both genetic and environmental factors. However, the influence of genetic variations on its early development remains unclear. This study examined the association of 12 different polymorphisms with atherosclerosis severity in anterior descending coronary (DA, n = 103) and carotid arteries (CA, n = 66) of autopsied young adults (< 30 years old). Histological sections (H-E) were classified according to the American Heart Association. Polymorphisms in ACE, TNF-α (− 308G/A and − 238 G/A), IFN-γ (+ 874 A/T), MMP-9 (− 1562 C/T), IL-10 (− 1082 A/G and − 819 C/T), NOS3 (894 G/T), ApoA1 (rs964184), ApoE (E2E3E4 isoforms), and TGF-β (codons 25 and 10) genes were genotyped by gel electrophoresis or automatic DNA sequencing. Firearm projectile or car accident was the main cause of death, and no information about classical risk factors was available. Histological analysis showed high prevalence of type III atherosclerotic lesions in both DA (69%) and CA (39%) arteries, while severe type IV and V lesions were observed in 14% (DA) and 33% (CA). Allele frequencies and genotype distributions were determined. Among the polymorphisms studied, IFN-γ and IL-10 (− 1082 A/G) were related to atherosclerosis severity in DA artery. No association between genotypes and lesion severity was found in CA. In conclusion, we observed that the high prevalence of early atherosclerosis in young adults is associated with IFN-γ (p < 0.001) and IL-10 (p = 0.013) genotypes. This association is blood vessel dependent. Our findings suggest that the vascular system presents site specialization, and specific genetic variations may provide future biomarkers for early disease identification.

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Twelve SNPs were associated with atherosclerosis severity in autopsied young adults.

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We found high prevalence of type III lesions in coronary and carotid arteries.

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Even severe lesions (types IV and V) were found in DA (14%) and CA (33%) arteries.

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Lesion severity was associated with IL-10 and IFN-γ genotype.

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The association was observed only in coronary, but not in carotid artery.

Thicker Carotid Intima Media Thickness in Children with Monocyte Chemoattractant Protein-1: A-2138T and A-2464G Mutation

Carotid intima media thickness (CIMT) is clearly associated with atherosclerosis. Studies in ischemic stroke patients reveal that there is a significant association between CIMT with monocyte chemoattractant protein-1 (MCP-1) and osteopontin (OPN) promoter polymorphism. This research aims to explain the effect of MCP-1 and OPN promoter polymorphism toward CIMT changes identified in Javanese Indonesian children. Subjects were 54 children: 27 were from parents with ischemic stroke (cases), and 27 were from healthy parents (controlled). The CIMT was examined by utilizing high resolution B-mode ultrasound. Physical examination and genotyping analysis of MCP-1 promoter were conducted by employing PCR method. Research results indicate that two polymorphisms were obtained, that is, A-2138T and G-2464A, respectively. A-2138T polymorphism was found in 5% of case children and in 14.3% of controlled children. G-2464A polymorphism was found in 5% of case children. CIMT of case children was significantly different from that of controlled children (0.61 ± 0.012 mm versus, 0.52 ± 0.015 mm, P = 0.021). Subjects with MCP-1 promoter polymorphism have 1.471 times higher tendency to have thicker CIMT than subjects with no polymorphism in MCP1 promoter. OPN promoter T-66G was also studied but it did not indicate occurrence of polymorphism in samples.

Genetic architecture of carotid artery intima-media thickness in Mexican Americans

BACKGROUND- Intima-media thickness (IMT) of the common and internal carotid arteries is an established surrogate for atherosclerosis and predicts risk of stroke and myocardial infarction. Often IMT is measured as the average of these 2 arteries; yet, they are believed to result from separate biological mechanisms. The aim of this study was to conduct a family-based genome-wide association study (GWAS) for IMT to identify polymorphisms influencing IMT and to determine if distinct carotid artery segments are influenced by different genetic components. METHODS AND RESULTS- IMT for the common and internal carotid arteries was determined through B-mode ultrasound in 772 Mexican Americans from the San Antonio Family Heart Study. A GWAS using 931219 single-nucleotide polymorphisms was undertaken with 6 internal and common carotid artery IMT phenotypes using an additive measured genotype model. The most robust association detected was for 2 single-nucleotide polymorphisms (rs16983261, rs6113474; P=1.60e(-7)) in complete linkage disequilibrium on chromosome 20p11 for the internal carotid artery near wall, next to the gene PAX1. We also replicated previously reported GWAS regions on chromosomes 19q13 and 7q22. We found no overlapping associations between internal and common carotid artery phenotypes at P<5.0e(-6). The genetic correlation between the 2 carotid IMT arterial segments was 0.51. CONCLUSIONS- This study represents the first large-scale GWAS of carotid IMT in a non-European population and identified several novel loci. We do not detect any shared GWAS signals between common and internal carotid arterial segments, but the moderate genetic correlation implies both common and unique genetic components.

Personalized medicine in cardiovascular diseases

Personalized medicine is a novel medical model with all decisions and practices being tailored to individual patients in whatever ways possible. In the era of genomics, personalized medicine combines the genetic information for additional benefit in preventive and therapeutic strategies. Personalized medicine may allow the physician to provide a better therapy for patients in terms of efficiency, safety and treatment length to reduce the associated costs. There was a remarkable growth in scientific publication on personalized medicine within the past few years in the cardiovascular field. However, so far, only very few cardiologists in the USA are incorporating personalized medicine into clinical treatment. We review the concepts, strengths, limitations and challenges of personalized medicine with a particular focus on cardiovascular diseases (CVDs). There are many challenges from both scientific and policy perspectives to personalized medicine, which can overcome them by comprehensive concept and understanding, clinical application, and evidence based practices. Individualized medicine serves a pivotal role in the evolution of national and global healthcare reform, especially, in the CVDs fields. Ultimately, personalized medicine will affect the entire landscape of health care system in the near future.

Genetics of ischemic stroke, stroke-related risk factors, stroke precursors and treatments

Stroke remains a leading cause of death worldwide and the first cause of disability in the western world. Ischemic stroke (IS) accounts for almost 80% of the total cases of strokes and is a complex and multifactorial disease caused by the combination of vascular risk factors, environment and genetic factors. Investigations of the genetics of atherosclerosis and IS has greatly enhanced our knowledge of this complex multifactorial disease. In this article we sought to review common single-gene disorders relevant to IS, summarize candidate gene and genome-wide studies aimed at discovering genetic stroke risk factors and subclinical phenotypes, and to briefly discuss pharmacogenetics related to stroke treatments. Genetics of IS is, in fact, one of the most promising research frontiers and genetic testing may be helpful for novel drug discoveries as well as for appropriate drug and dose selection for treatment of patients with cerebrovascular disease.

Meta-analysis of genome-wide association studies from the CHARGE consortium identifies common variants associated with carotid intima media thickness and plaque

Carotid intima media thickness (cIMT) and plaque determined by ultrasonography are established measures of subclinical atherosclerosis that each predicts future cardiovascular disease events. We conducted a meta-analysis of genome-wide association data in 31,211 participants of European ancestry from nine large studies in the setting of the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. We then sought additional evidence to support our findings among 11,273 individuals using data from seven additional studies. In the combined meta-analysis, we identified three genomic regions associated with common carotid intima media thickness and two different regions associated with the presence of carotid plaque (P < 5 × 10(-8)). The associated SNPs mapped in or near genes related to cellular signaling, lipid metabolism and blood pressure homeostasis, and two of the regions were associated with coronary artery disease (P < 0.006) in the Coronary Artery Disease Genome-Wide Replication and Meta-Analysis (CARDIoGRAM) consortium. Our findings may provide new insight into pathways leading to subclinical atherosclerosis and subsequent cardiovascular events.

Cerebrovascular atherosclerosis in type III hyperlipidemia is modulated by variation in the apolipoprotein A5 gene

Objective

Type III Hyperlipoproteinemia is a rare lipid disorder with a frequency of 1-5 in 5000. It is characterized by the accumulation of triglyceride rich lipoproteins and patients are at increased risk of developping atherosclerosis. Type III HLP is strongly associated with the homozygous presence of the ε2 allele of the APOE gene.

However only about 10% of subjects with APOE2/2 genotype develop hyperlipidemia and it is therefore assumed that further genetic and environmental factors are necessary for the expression of disease. It has recently been shown that variation in the APOA5 gene is one of these co-factors. The aim of this study is to investigate the development of cerebrovascular atherosclerosis in patients with Type III hyperlipoproteinemia (Type III HLP) and the role of variation in the APOA5 gene as a risk factor.

Methods

60 patients with type III hyperlipidemia and ApoE2/2 genotype were included in the study after informed consent. The presence of cerebrovascular atherosclerosis was investigated using B-mode ultra-sonography of the carotid artery. Serum lipid levels were measured by standard procedures. The APOE genotype and the 1131T > C and S19W SNPs in the APOA5 gene and the APOC3 sstI SNP were determined by restriction isotyping Allele frequencies were determined by gene counting and compared using Fisher's exact test. Continuous variables were compared using the Mann Whitney test. A p value of 0.05 or below was considered statistically significant. Analysis was performed using Statistica 7 software.

Results

The incidence of the APOA5 SNPs, -1131T > C and S19W and the APOC3 sstI SNP were determined as a potential risk modifier. After correction for conventional risk factors, the C allele of the 1131T > C SNP in the APOA5 gene was associated with an increased risk for the development of carotid plaque in patients with Type III HLP with an odds ratio of 3.69. Evaluation of the genotype distribution was compatible with an independent effect of APOA5.

Conclusions

The development of atherosclerosis in patients with Type III HLP is modulated by variation in the APOA5 gene.

Non-invasive vessel examinations in carriers of LDL-receptor defective gene versus non-carriers with newly detected asymptomatic severe hypercholesterolemia

The results of the research of early vascular alterations in LDL-R carriers in comparison with those in non-carriers with severe hypercholesterolemia are controversial.

AIM

To investigate the difference between severe hypercholesterolemia patients that carry LDL-R defective gene and those that do not have it, in their functional (flow-mediated vasodilation) and structural (intima-media thickness of carotid artery and ankle-brachial index) characteristics of arterial wall.

PATIENTS AND METHODS

The study included 120 hypercholesterolemic patients. Biochemistry parameters were studied by routine methods. The flow-mediated vasodilation (%FMD), ankle-brachial index (ABI) and intima-media thickness (IMT) of common carotid artery were determined using Hewlett Packard Sonos 5 500; MedicaSoft. IMT.lab was the software programme used in the study.

RESULTS

There was no significant difference between the groups with respect to total cholesterol, LDL, HDL, Apo-B, Apo-A1, cellular adhesion molecules (sICAM-1, sVCAM-1, sP- and sE-selectine). The Apo-B/Apo A1 index differed significantly (t = 11.23, p < 0.001) between the two groups; there was difference even after adjustment for age. There was no significant difference in the endothelial dependent and independent vasodilatation between the examined groups (p > 0.05). We found a significantly greater carotid IMT and lower ABI in the carriers than the respective parameters in the non-carriers. This significant difference was confirmed after adjustment for age.

CONCLUSION

Our data show that LDL-R carriers have a higher carotid IMT and lower ABI than non-carriers, whereas no difference between the groups was found with respect to the level of lipid parameters and %FMD.

Cholesteryl ester transfer protein and hepatic lipase gene polymorphisms: effects on hepatic mRNA levels, plasma lipids and carotid atherosclerosis

OBJECTIVE

HDL modifying effects of cholesteryl ester transfer protein (CETP) and hepatic lipase (LIPC) depend in part on each other. We studied associations of CETP-Taq1B and -514C>T-LIPC polymorphisms with hepatic mRNA levels, and their combined effects on plasma lipids and carotid atherosclerosis.

METHODS

We genotyped the CETP-Taq1B and the -514C>T-LIPC polymorphisms in 67 obese women in whom hepatic CETP and LIPC transcript levels were determined as well as in 1549 participants of the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR). Carotid atherosclerosis was assessed by intima-media thickness and extent of plaques (B-score) of the carotid arteries.

RESULTS

In obese women, CETP-Taq1B and -514C>T-LIPC variant alleles were associated with reduced hepatic levels of CETP and LIPC mRNA, respectively. The CETP and LIPC polymorphisms accounted for 12.9 and 14.4% of the variability in respective transcripts. In the SAPHIR population, CETP-Taq1B showed independent effects on LDL diameter, HDL and LDL cholesterol, apolipoproteins AI and B and cholesterol/HDL cholesterol, while -514C>T-LIPC revealed independent effects on HDL cholesterol and apolipoprotein AI. The two polymorphisms displayed interactions at the level of HDL cholesterol. Compared to subjects carrying wild-type alleles at both loci, subjects homozygous for the CETP wild-type allele, but heterozygous for the LIPC polymorphism and subjects heterozygous for the CETP polymorphism, but homozygous for the LIPC wild-type allele showed an increased risk of carotid atherosclerosis (both P<0.05).

CONCLUSIONS

CETP and LIPC polymorphisms influence the respective hepatic transcript levels, demonstrate interactions on HDL cholesterol and suggest that imbalances between CETP and LIPC activities may modulate the risk of carotid atherosclerosis.

Carotid artery atherosclerosis in hypertensive patients with a functional LDL receptor-related protein 6 gene variant

BACKGROUND AND AIMS

Rare (611C) and common (1062V) variants of the Low-Density Lipoprotein Receptor-Related Protein 6 (LRP6) display reduced activation of Wnt/ß-catenin signaling. The rare gene variant was associated with hypertension, metabolic abnormalities, and early coronary artery disease. We investigated whether the common 1062V LRP6 variant was related to carotid artery atherosclerosis (CAA) in hypertensive patients.

METHODS AND RESULTS

Retrospective study of 334 hypertensive patients (<65 years old) who underwent carotid artery ultrasonography. Hypertension, type 2 diabetes, dyslipidemia, glomerular filtration rate, and smoking habit were evaluated. CAA was defined by the presence of atherosclerotic plaques (focal intima-media thickness ≥ 1.3 mm). Logistic regression models were used to estimate the independent effect of 1062V allele. The relationship between LRP6 genotypes and LRP6 gene expression in carotid plaques was also investigated. No difference was observed between genotypes in clinical variables except for a slightly higher fasting glucose in 1062V carriers. The 1062V LRP6 variant was an independent risk factor for CAA in both unadjusted (OR 2.08, 95%CI 1.27-3.41, p=0.003) and adjusted models (OR 1.92, 95%CI 1.09-3.39, p=0.02). LRP6 was expressed in carotid atherosclerotic plaques at significantly lower levels (p=0.015) in 1062V carriers.

CONCLUSION

Beside the role of established risk factors, 1062V variant of LRP6 and CAA are strongly associated in hypertensive patients, making LRP6 a novel relevant candidate gene for atherosclerosis in the presence of hypertension.

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.

Cardiovascular genomics, personalized medicine, and the National Heart, Lung, and Blood Institute: part I: the beginning of an era

The inaugural issue of Circulation: Cardiovascular Genetics arrives at a remarkable time in the history of genetic research and cardiovascular medicine. Despite tremendous progress in knowledge gained, cardiovascular disease(CVD) remains the leading cause of death in the United States,1 and it has overcome infectious diseases as the leading cause of death worldwide.2 In addition, rates of CVD remain higher in black and Hispanic populations in the United States.1 The recent Strategic Plan of the National Heart, Lung,and Blood Institute (NHLBI) emphasizes research areas to fill the significant knowledge gaps needed to improve the diagnosis,treatment, and control of known risk factors and clinically apparent disease. Simultaneously, the NHLBI Strategic Plan recognizes a tremendous opportunity that is available for use of genetic and genomic research to generate new knowledge that might reduce the morbidity and mortality from CVD in US populations.3 Public availability of vast amounts of detailed sequence information about the human genome, completed sequence data on dozens of other animal genomes, and private sector development of high-throughput genetic technologies has transformed in a few short years the conduct of cardiovascular genetics and genomics research from a primary focus on mendelian disorders to a current emphasis on genome-wide association studies (GWAS; Figure1). In this review, we describe the rationale for the current emphasis on large-scale genomic studies, summarize the evolving approaches and progress to date, and identify immediate-term research needs. The National Institutes of Health (NIH) and the NHLBI are supporting a portfolio of large-scale genetic and genomic programs in diverse US populations with the longer-term objective of translating knowledge into the prediction, prevention, and preemption of CVD, as well as lung, sleep, and blood disorders. Underlying this portfolio is a strong commitment to make available participant-level data and aggregate research results to the broad community of investigators, while protecting the privacy and confidentiality and respecting the informed consent of study participants.

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.

Multi-ethnic genetic association study of carotid intima-media thickness using a targeted cardiovascular SNP microarray

BACKGROUND AND PURPOSE

Identification of subclinical atherosclerosis by ultrasonographic measurement of carotid intima-media thickness (IMT) is a validated tool, in conjunction with traditional risk factors, for clinical assessment of cardiovascular disease risk. IMT has also been recognized as a quantitative measure of cardiovascular disease progression in asymptomatic individuals, and many candidate gene association studies have attempted to identify genetic variants associated with interindividual differences in IMT with limited success. We sought to test the association between subclinical atherosclerosis measured by IMT and approximately 50,000 SNPs, densely mapping approximately 2100 genes found on the gene-centric Illumina cardiovascular disease beadchip in a multi-ethnic population-based sample.

METHODS

IMT was measured by B-mode ultrasound and DNA was collected from a population-based sample of South Asian (n=328), Chinese (n=302), and European Caucasian (n=268) participants. Genetic association was measured using multivariate linear regression including adjustment for covariates.

RESULTS

The most robust association across all models tested was observed for a SNP (rs3791398) in histone deacetylase 4 (HDAC4; P=1.8e-5 to P=3.6e-5), while another strong association signal was observed with natriuretic peptide receptor a/guanylate cyclase A (NPR1) (rs10082235, P=5.4e-5). Seven of 13 previously reported functional candidate genes contained a SNP that was marginally associated (0.01 < P < or = 0.05).

CONCLUSION

This initial multi-ethnic high-density association study of carotid IMT suggests some novel loci requiring further evaluation in follow-up studies.

Heritability and linkage analysis for carotid intima-media thickness: the family study of stroke risk and carotid atherosclerosis

BACKGROUND AND PURPOSE

The aim of this study was to identify quantitative trait loci (QTL) for carotid intima-media thickness (CIMT) a risk factor for stroke and cardiovascular disease.

METHODS

Probands were selected from Caribbean Hispanic subjects of the population-based Northern Manhattan Study. CIMT was measured by high-resolution B-mode ultrasound and expressed as the mean (IMTx) and mean of the maximum (IMTm). Variance components methodology was used to detect linkage using SOLAR and calculate locus-specific heritability. Ordered-subset Analysis was done based on history of hypertension and total cholesterol levels.

RESULTS

Among 100 Dominican families, 1390 subjects had CIMT measured (848 females; mean age 46.2 years). CIMT had a heritability of 0.65 after adjusting for age, age(2), sex, cigarette pack-years, waist hip ratio, and BMI. Adjusted maximum multipoint LOD scores >2 were found on chromosomes 14q (D14S606) and 7p (D7S817). Linkage to chromosome 14q was significantly increased in a subset of families with the greatest history of hypertension (MLOD=4.12). The QTL on Ch14q accounted for 0.21 of the heritability of IMTm, and on Ch7p 0.27 of the heritability of BIFm.

CONCLUSIONS

Several QTLs for CIMT were found on chromosomes 7p and 14q. The QTL on 14q replicates a suggestive linkage peak delimited in the Framingham Heart Study. These QTLs accounted for a substantial amount of trait heritability and warrant further fine mapping.

Polymorphisms of the methylenetetrahydrofolate reductase, vascular endothelial growth factor, endothelial nitric oxide synthase, monocyte chemoattractant protein-1 and apolipoprotein E genes are not associated with carotid intima-media thickness

BACKGROUND

Single nucleotide polymorphisms in the 5,10-methylenetetrahydrofolate reductase (MTHFR), vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), monocyte chemoattractant protein-1 (MCP-1) and apolipoprotein E (ApoE) genes appear to be a genetic risk factor for atherosclerosis. Common carotid intima-media thickness (cIMT) provides information on the severity of atherosclerosis.

OBJECTIVE

To investigate the relationship between cIMT and gene polymorphisms associated with atherosclerosis in Turkish patients with coronary artery disease (CAD).

METHODS

Sixty-two patients with angiographically diagnosed stable CAD were divided into two groups according to their cIMT values (group 1: n=35, cIMT of 1 mm or greater; group 2: n=27, cIMT of less than 1 mm). MTHFR 677 C/T, VEGF --460 C/T, eNOS 894 G/T, MCP-1 --2518 A/G and ApoE (E2, E3 and E4) gene polymorphisms (where A is adenine, C is cytosine, G is guanine and T is thymine) were analyzed by polymerase chain reaction and restriction fragment length polymorphism. Evaluations of cardiovascular risk factors and coronary atherosclerotic lesions were performed in all patients. Serum homocysteine and high-sensitivity C-reactive protein were measured and compared between the two groups.

RESULTS

Serum high-sensitivity C-reactive protein (P=0.04) and homocysteine (P=0.006) levels were higher in group 1 than in group 2. The ratio of multivessel CAD and previous myocardial infarction was significantly higher in group 1 than in group 2 (P=0.014). In the study population, no significant difference in cIMT was observed according to the polymorphisms studied. Only hyperhomocysteinemia (OR 1.17 [95% CI 1.01 to 1.35], P=0.033) and previous myocardial infarction (OR 3.76 [95% CI 1.10 to 12.81], P=0.034) maintained a significant correlation with cIMT on multiple logistic regression analysis.

CONCLUSION

cIMT is increased in patients with hyperhomocysteinemia, inflammation and extended CAD. MTHFR 677 C/T, VEGF --460 C/T, eNOS 894 G/T, MCP-1 --2518 A/G and ApoE single nucleotide polymorphisms were not associated with increased cIMT.

Personalized Medicine in Coronary Artery Disease: Insights From Genomic Research

Prior clinical studies have demonstrated that a family history of coronary artery disease (CAD) is associated with future cardiovascular events. Although there are several Mendelian disorders that are associated with CAD, most common forms of CAD are believed to be multifactorial and the result of many genes with small individual effects. The identification of these genes and their variation would be very helpful for the prediction, prevention, and management of CAD; linkage analysis or candidate gene case-control studies have been largely unsuccessful. On the contrary, recent advances in genomic techniques have generated a large amount of deoxyribonucleic acid (DNA)-based information. The link between CAD and inflammation and biological pathways has been highlighted. In particular, several genome-wide association studies have replicated a novel gene marker on chromosome 9p21. The information gained from genomic studies, in combination with clinical data, is expected to refine personalized approaches to assess risk and guide management for CAD. Genetic risk scores derived from several functional single nucleotide polymorphisms (SNPs) or haplotypes in multiple genes may improve the prediction of CAD. Despite the complexity of CAD genetics, steady progress is expected.

Carotid atherosclerosis in familial combined hyperlipidemia associated with the APOB/APOA-I ratio

OBJECTIVES

The effects of risk factors on carotid atherosclerosis in familial combined hyperlipidemia (FCHL) remain unclear. We assessed carotid intima-media thickness (IMT) and plaque in relation to classical risk factors and apolipoprotein A-I (apoA-I) and B (apoB) levels in patients with FCHL.

METHODS AND RESULTS

We included 131 unrelated FCHL patients (27 with prior cardiovascular disease (CVD)) diagnosed by standard criteria and 190 age- and sex-matched control subjects. Cardiovascular risk factors were assessed and IMT in the far wall of all carotid segments and plaque burden were determined in FCHL patients and controls. All carotid measurements were increased in FCHL patients compared to controls (P<0.001), irrespective of CVD status. For asymptomatic FCHL, the adjusted difference in mean common carotid IMT was 0.08 mm, corresponding to approximately 16 years of physiological IMT increase. By multivariate analysis in a model with all risk factors, inclusive of the metabolic syndrome, independent associations of IMT were age, the apoB/apoA-I ratio, systolic blood pressure, fasting glucose, family history of CVD and total/HDL cholesterol ratio (r(2)=0.475, P<0.001). The strongest determinant of IMT was the apoB/apoA-I ratio (beta=0.422, P<0.001).

CONCLUSIONS

Patients with FCHL have increased carotid IMT that is strongly related to the apoB/apoA-I ratio, a measure of overall lipid abnormalities. The findings support the atherogenicity of the lipid phenotype in FCHL beyond associated risk factors. They also have implications for diagnosis and management of CVD risk in this condition.

Association between the paraoxonase-1 192Q>R allelic variant and coronary endothelial dysfunction in patients with early coronary artery disease

OBJECTIVE

To test the hypothesis that allelic variants of the paraoxonase-1 gene are associated with endothelial dysfunction, an early stage of atherosclerosis.

PATIENTS AND METHODS

We assessed 192Q>R and 55L>M allelic variants of the paraoxonase gene and coronary endothelial function in response to intracoronary acetylcholine in 99 patients (52 with homozygous QQ, 47 with homozygous RR or heterozygous QR). The study was conducted from September 1, 2002, through November 30, 2004.

RESULTS

Of 52 homozygous QQ patients, 39 (75%) had endothelial dysfunction vs 20 (43%) of the 47 RR/QR patients (P=.001), and this association remained significant after adjustment in a multivariable linear regression model (P=.005). In homozygous QQ vs RR/QR patients, epicardial arterial diameter decreased more (% change in diameter, -22%+/-21% vs -9%+/-16%, respectively, P=.002), coronary blood flow increased less (+37%+/-77% vs +75%+/-75%, P=.02) in response to acetylcholine, and oxidized LDL levels were higher. The 55L>M allelic variant was not significantly associated with endothelial dysfunction and had no effect on the association between endothelial dysfunction and the 192Q>R allelic variant.

CONCLUSION

The 192Q>R allelic variant of the paraoxonase-1 gene is associated with coronary endothelial dysfunction. The current study provides further information regarding the potential mechanisms by which this allelic variant contributes to early atherosclerosis in humans.

Adiponectin gene polymorphism 45T>G is associated with carotid artery plaques in patients with type 2 diabetes mellitus

Adiponectin has been reported to have a wide range of antiatherogenic actions. Two common single nucleotide polymorphisms (SNPs) at the adiponectin locus (45T>G and 276G>T) have been reported to be associated with diabetes and cardiovascular diseases. The aim of this study was to examine the association between common polymorphisms of the adiponectin gene (ACDC) and carotid atherosclerosis in patients with type 2 diabetes mellitus. A total of 708 unrelated patients with type 2 diabetes mellitus were recruited. SNP45 and SNP276 ACDC were genotyped, and B-mode ultrasonography of the carotid arteries was performed to measure carotid intima-media thickness and assess the presence of carotid artery plaques (CAP). Although there was no significant difference in carotid intima-media thickness according to ACDC genotype, subjects carrying the SNP45 GG genotype had a significantly higher risk of having CAP (odds ratio, 2.468; P = .045) compared with carriers of the T allele after adjustment for possible confounding factors. This study suggests that the GG genotype at ACDC SNP45 is associated with the presence of CAP and may contribute to atherosclerosis in type 2 diabetes mellitus.

Genome-wide association study for subclinical atherosclerosis in major arterial territories in the NHLBI's Framingham Heart Study

INTRODUCTION

Subclinical atherosclerosis (SCA) measures in multiple arterial beds are heritable phenotypes that are associated with increased incidence of cardiovascular disease. We conducted a genome-wide association study (GWAS) for SCA measurements in the community-based Framingham Heart Study.

METHODS

Over 100,000 single nucleotide polymorphisms (SNPs) were genotyped (Human 100K GeneChip, Affymetrix) in 1345 subjects from 310 families. We calculated sex-specific age-adjusted and multivariable-adjusted residuals in subjects tested for quantitative SCA phenotypes, including ankle-brachial index, coronary artery calcification and abdominal aortic calcification using multi-detector computed tomography, and carotid intimal medial thickness (IMT) using carotid ultrasonography. We evaluated associations of these phenotypes with 70,987 autosomal SNPs with minor allele frequency > or = 0.10, call rate > or = 80%, and Hardy-Weinberg p-value > or = 0.001 in samples ranging from 673 to 984 subjects, using linear regression with generalized estimating equations (GEE) methodology and family-based association testing (FBAT). Variance components LOD scores were also calculated.

RESULTS

There was no association result meeting criteria for genome-wide significance, but our methods identified 11 SNPs with p < 10(-5) by GEE and five SNPs with p < 10(-5) by FBAT for multivariable-adjusted phenotypes. Among the associated variants were SNPs in or near genes that may be considered candidates for further study, such as rs1376877 (GEE p < 0.000001, located in ABI2) for maximum internal carotid artery IMT and rs4814615 (FBAT p = 0.000003, located in PCSK2) for maximum common carotid artery IMT. Modest significant associations were noted with various SCA phenotypes for variants in previously reported atherosclerosis candidate genes, including NOS3 and ESR1. Associations were also noted of a region on chromosome 9p21 with CAC phenotypes that confirm associations with coronary heart disease and CAC in two recently reported genome-wide association studies. In linkage analyses, several regions of genome-wide linkage were noted, confirming previously reported linkage of internal carotid artery IMT on chromosome 12. All GEE, FBAT and linkage results are provided as an open-access results resource at http://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?id=phs000007 webcite.

CONCLUSION

The results from this GWAS generate hypotheses regarding several SNPs that may be associated with SCA phenotypes in multiple arterial beds. Given the number of tests conducted, subsequent independent replication in a staged approach is essential to identify genetic variants that may be implicated in atherosclerosis.

Relevance of Genetics and Genomics for Prevention and Treatment of Cardiovascular Disease

Atherosclerotic cardiovascular disease (CVD) is a major health problem in the United States and around the world. Evidence accumulated over decades convincingly demonstrates that family history in a parent or a sibling is associated with atherosclerotic CVD, manifested as coronary heart disease, stroke, and/or peripheral arterial disease. Although there are several mendelian disorders that contribute to CVD, most common forms of CVD are believed to be multifactorial and to result from many genes, each with a relatively small effect working alone or in combination with modifier genes and/or environmental factors. The identification and the characterization of these genes and their modifiers would enhance prediction of CVD risk and improve prevention, treatment, and quality of care. This scientific statement describes the approaches researchers are using to advance understanding of the genetic basis of CVD and details the current state of knowledge regarding the genetics of myocardial infarction, atherosclerotic CVD, hypercholesterolemia, and hypertension. Current areas of interest and investigation--including gene-environment interaction, pharmacogenetics, and genetic counseling--are also discussed. The statement concludes with a list of specific recommendations intended to help incorporate usable knowledge into current clinical and public health practice, foster and guide future research, and prepare both researchers and practitioners for the changes likely to occur as molecular genetics moves from the laboratory to clinic.

B-group vitamins, MTHFR C677T polymorphism and carotid intima-media thickness in clinically healthy subjects

OBJECTIVE

Plasma B-group vitamins and age may affect the carotid intima-media thickness (IMT) in subjects with different 677TT genotype of the methylenetetrahydrofolate reductase (MTHFR) gene.

DESIGN

A hospital-based cross-study.

SETTING

Genomic and Vascular Center, Changhua Christian Hospital, Changhua, Taiwan.

SUBJECTS

Five hundred and forty-one clinically healthy subjects.

INTERVENTION

Fasting plasma, homocysteine (Hcy), vitamin B(6), vitamin B(12), folate and B-mode carotid ultrasound.

RESULTS

MTHFR genotype, plasma concentrations of folate, vitamin B(6) and vitamin B(12) and age were significantly correlated to the plasma Hcy concentration. MTHFR 677TT carriers had higher concentrations of Hcy than did subjects with the CC and CT genotypes. Age, sex, body mass index and plasma Hcy were independent contributors to increase carotid IMT. However, with stratification by mean value of age and B-group vitamins concentrations, we found that at advanced age, lower plasma folate and vitamin B(12) were three risk factors involved in the enhancing effect of the MTHFR 677TT genotype on the increase of plasma Hcy and carotid IMT.

CONCLUSION

MTHFR 677TT-related carotid atherosclerosis was only identified in healthy elderly subjects with lower level of plasma folate and vitamin B(12).

SPONSORSHIP

Changhua Christian Hospital.

New Insight Into the Association of Apolipoprotein E Genetic Variants With Carotid Plaques and Intima-Media Thickness

BACKGROUND AND PURPOSE

Carotid plaques and elevated carotid artery intima-media thickness (IMT) are major predictors of vascular morbidity and mortality. Our aim was to test their association with 2 polymorphisms of the apolipoprotein E (apoE) gene, epsilon and -219G/T.

METHODS

The study was performed on 5856 subjects aged > or =65 years recruited from the French population for the Three-City Study. Carotid ultrasound examination included an assessment of atherosclerotic plaques in the extracranial carotid arteries and a measurement of IMT in the common carotid arteries (CCA) at a site free of plaques. The genetic association was tested using genotype and haplotype analyses.

RESULTS

In a multivariate analysis including both polymorphisms and vascular risk factors, carotid plaques were more frequent in epsilon4 homozygotes (adjusted odds ratio=2.12, 95% CI=1.27 to 3.53) and less frequent in epsilon2 carriers (adjusted odds ratio=0.79, 95% CI=0.66 to 0.95) compared with epsilon3 homozygotes. Adjusting for and stratifying on lipid levels did not modify these results. CCA-IMT was higher in carriers of the epsilon34 genotype (mean CCA-IMT=0.744 mm versus 0.732 mm for the epsilon33 genotype, P=0.002), but the association disappeared after excluding subjects with carotid plaques. No association was found between the -219 polymorphism and either carotid plaques or CCA-IMT, and there was no interaction or cis-effect between -219 and epsilon.

CONCLUSIONS

This study, conducted on a large population cohort of French elderly, demonstrated that carotid plaques were significantly associated with the apoE epsilon polymorphism independently of the -219 polymorphism and vascular risk factors, in particular lipid levels.

Parental Longevity, Carotid Atherosclerosis, and Aortic Arterial Stiffness in Adult Offspring

BACKGROUND AND PURPOSE

We examined the associations of parental longevity with carotid intima-media thickness, carotid plaques, and aortic arterial stiffness in adult offspring.

METHODS

A population of 1117 volunteers who participated in the SUVIMAX Vascular Study (mean age, 59.7 years; 49.0% women) were included. Carotid-femoral pulse-wave velocity (PWV) was used to assess aortic stiffness. Carotid B-mode ultrasound examination included measurements (at sites free of plaque) of intima-media thickness at the common carotid arteries and assessment of atherosclerotic plaques in the extracranial carotid arteries.

RESULTS

The prevalence of carotid plaques in subjects whose fathers had died at <65 years, in those whose fathers were alive at 65 years but who had died by 80 years, and in those whose fathers were alive at 80 years was 40.4%, 30.4%, and 28.9%, respectively (P<0.001). The multivariate odds ratios of carotid plaques in the 3 groups of paternal longevity, adjusted for conventional cardiovascular risk factors, were 1, 0.68 (95% CI, 0.48 to 0.96), and 0.69 (95% CI, 0.49 to 0.98), respectively. The mean common carotid arteries intima-media thickness was higher in subjects with premature paternal death in univariate (P<0.007) but not in multivariate (P=0.39) analyses. Mean PWV decreased with increasing paternal longevity in both univariate and multivariate analyses. The multivariate-adjusted means of PWV in the 3 groups of paternal longevity were 11.9+/-0.14, 11.7+/-0.12, and 11.0+/-0.12 m/s (P<0.0001), respectively. In contrast, neither B-mode ultrasound measurements nor PWV measurements were associated with maternal longevity.

CONCLUSIONS

These results may indicate that there are modifications of structure and function of large arteries according to paternal longevity.

Associations of PPARGC1A haplotypes with plaque score but not with intima-media thickness of carotid arteries in middle-aged subjects

BACKGROUND AND PURPOSE

Peroxisome proliferator activated receptor gamma coactivator 1alpha (PGC-1alpha, PPARGC1A) integrates the transcriptional program of mitochondrial biogenesis. Mitochondria are the main source of cellular reactive oxygen species implicated in atherogenesis. We therefore ascertained associations of PPARGC1A polymorphisms with asymptomatic carotid atherosclerosis.

METHODS

Eight single nucleotide polymorphisms tagging two haplotype blocks within PPARGC1A were studied in 1379 participants of the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk. Early atherosclerosis was assessed by intima-media thickness and extent of plaques (B-score) of the carotid arteries.

RESULTS

No associations of carotid artery intima-media thickness measurements with block 1 or 2 haplotype distributions or individual haplotypes were observed. However, the block 1 haplotype carrying the variant C nucleotide at -3974 relative to the transcription start site was associated with disease status defined by the presence of more than one minimal lesion and the -3974 C allele was associated with decreased risk (odds ratio=0.60, P=0.007) after adjustment for linkage disequilibrium between single nucleotide polymorphisms.

CONCLUSIONS

These result are consistent with the concept that risk factors for distinct carotid phenotypes may vary and suggest, but do not prove, that PGC-1alpha may contribute to the regulation of atherogenic pathways.

Thematic review series: Patient-Oriented Research. Imaging atherosclerosis: state of the art

The ability to image obstructive arterial disease brought about a revolution in clinical cardiovascular care; the development of newer technologies that image arterial wall thicknesses, areas, volumes, and composition allows valid imaging of atherosclerosis for the first time. Development of noninvasive imaging of atherosclerosis has further led to a quantum shift in research in the field by enabling the study of asymptomatic populations and thus allowing investigators to focus on preclinical disease without the many biases associated with the study of symptomatic patients. These noninvasive investigations have broad implications for clinical care as well. Coronary angiography, computed tomographic (CT) imaging of coronary calcium, intravascular ultrasound, multidetector CT angiography, B mode ultrasound of the carotid arteries, and MRI of the carotid arteries all have unique strengths and weaknesses for imaging atherosclerosis. Certain of these techniques are extremely useful as outcome variables for clinical trials, and others are uniquely useful as predictors of the risk of cardiovascular disease. All are informative in one way or another with regard to the role of plaque remodeling and composition in disease causation. CT and MRI technology are advancing very rapidly, and research and clinical uses of these imaging modalities promise to further advance our understanding of atherosclerosis and its prevention.

Genetic determinants of carotid ultrasound traits

Atherosclerosis is a complex disease with various intermediate phenotypes that are themselves complex and influenced by many factors. Through the use of carotid ultrasound techniques, the intermediate stages of vascular disease can be imaged and studied for association with potential genetic determinants. In this article we review the most recent available data (reports published since 2004) on the genetic determinants of atherosclerosis, as measured by one-, two-, and three-dimensional ultrasonography of the carotid arteries. In general, associations are disparate and modest. For intima-media thickness, promising associations have been found for both TNFRSF1A R92Q and PPARG P12A, but associations also differed in the same individuals depending on the specific ultrasound trait studied (eg, linear intima-media thickness versus total plaque volume in carotid arteries). Some of the challenging issues for future studies include accounting for gene-environment interactions, sex-specific associations, and the distinctiveness of different carotid ultrasound measures.

The 460Trp allele of α-adducin increases carotid intima–media thickness in young adult males

BACKGROUND

The 460Trp allele of the alpha-adducin gene (ADD1), which is involved in a form of salt-sensitive hypertension, has been associated with patterns of target organ damage.

OBJECTIVES

As carotid artery intima-media thickness (IMT) largely depends upon unknown genetic factors, besides being associated to conventional risk factors, we tested the association of the 460Trp allele of ADD1 with IMT in a well-characterized sample of young healthy normotensive subjects, to assess the role of ADD1 polymorphism without overlapping effects of age or already elevated blood pressure.

METHODS

Anthropometric measurements, blood pressure (BP), and carotid artery wall IMT (high-resolution sonography and digitalized morphometry) were obtained in 420 healthy normotensive Caucasian university students. Genotypes for ADD1 were detected by automated genomic polymerase chain reaction (PCR).

RESULTS

ADD1 genotypes were evenly distributed between genders. IMT was significantly larger in carriers of the 460Trp allele of ADD1, while a significant gender x ADD1 interaction (P = 0.02) demonstrated that IMT was increased only in males carrying the 460Trp allele (P < 0.001). No significant association was found in females.

CONCLUSIONS

The 460Trp allele of ADD1 contributes substantially to increase carotid IMT, in a male hormonal milieu only, at least in the young age range.

Influence of HDL cholesterol on preclinical carotid atherosclerosis in familial hypercholesterolemia

OBJECTIVE

The effect of risk factors on carotid atherosclerosis in heterozygous familial hypercholesterolemia (FH) is unclear. We evaluated carotid intima-media thickness (IMT) by sonography in relation to classical and emergent risk factors in a large FH cohort.

METHODS AND RESULTS

Risk factors and carotid IMT were assessed in 196 asymptomatic subjects aged > or =25 years fulfilling strict diagnostic criteria for clinical FH who were either undertreated or treatment-naive. Conventional risk factors, but not lipoprotein(a), homocysteine, or apolipoprotein E (apoE) genotypes were univariately related to IMT. Age-adjusted and gender-adjusted IMT increased with increasing low-density lipoprotein (LDL) cholesterol and decreased with increasing high-density lipoprotein (HDL) cholesterol. Compared with a total cholesterol/HDL ratio >5.0, a ratio < or =5.0 was associated with a lower adjusted IMT, with a mean difference of -0. 09 mm (95% confidence interval, -0.13 to -0.04). By multivariate analysis, age, HDL cholesterol (negatively), physical exercise, family history of early-onset coronary heart disease, LDL cholesterol, and leukocyte count, in this order, were independent associations of IMT (r2=0.429, P<0.001).

CONCLUSIONS

Traditional risk factors account for a sizeable proportion of variation in carotid IMT in FH. Because the HDL cholesterol level and the total cholesterol/HDL ratio are strong predictors of preclinical carotid atherosclerosis, HDL cholesterol-raising strategies should have an important therapeutic role in FH.

Association between well-characterized lipoprotein-related genetic variants and carotid intimal medial thickness and stenosis: The Framingham Heart Study

OBJECTIVE

To determine the association of well-characterized lipoprotein-related genetic variants with carotid intimal medial thickness (IMT) and stenosis.

METHODS

3380 men and women from the Framingham Offspring Study underwent carotid ultrasound to determine carotid IMT and stenosis>/=25%. We genotyped 12 variants in 10 lipoprotein-related genes known to be associated with significant differences in lipoprotein levels.

RESULTS

For most of the variants, there was no association with carotid IMT. In multivariable, sex-specific analyses, the rare allele of the cholesterol ester transfer protein (CETP) TaqIB variant was associated with lower ICA IMT in men. Hypertension was associated with higher ICA IMT only in male carriers of the rare allele of the APOCIII Sst-1 variant (p for the interaction=0.041). In analyses of carotid stenosis in male, carriers of the lipoprotein lipase (LPL) N291S rare variant showed a higher risk of carotid stenosis (OR=2.59, 95% confidence interval: 1.11-6.02, p=0.028) compared to NN genotype.

CONCLUSIONS

While there is no evidence for a significant association of several common lipoprotein-related genetic variants with carotid IMT, our results are consistent with the previously reported role of CETP and LPL genetic variants in cardiovascular risk and the possible modulation of the association between hypertension and carotid IMT by APOCIII Sst-1 variant.

Disparate Associations of a Functional Promoter Polymorphism in PCK1 With Carotid Wall Ultrasound Traits

Background and Purpose— Cytosolic phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32), encoded by PCK1 , catalyzes the first committed step in gluconeogenesis. We previously showed that a –232C>G promoter polymorphism within a cis -acting element required for basal and cAMP-mediated PCK1 gene transcription results in loss of negative regulation by insulin, contributing to worsened metabolic control in the context of insulin resistance. We hypothesized that this polymorphism would be associated with carotid atherosclerosis in a sample of 150 aboriginal Canadians.

Methods— Dependent variables were 2 distinct carotid traits, namely intima-media thickness (IMT) assessed using B-mode ultrasound and total carotid plaque volume (TPV) assessed using 3D ultrasound.

Results— Multivariate analysis showed significant but opposite associations of PCK1 genotype with these traits. Specifically, subjects with the PCK1 –232G/G genotype had more carotid IMT (0.80±0.02 versus 0.73±0.03 mm; P =0.007) but less TPV (0.10±0.09 versus 0.38±0.13; P =0.03) than subjects with other genotypes.

Conclusions— The findings connect the key enzyme in gluconeogenesis with atherosclerosis. The meaning of the opposing associations of PCK1 genotype with IMT and TPV is unclear; more work is required to confirm whether these might be distinct quantitative traits with different biological determinants.

Identifying novel genes for atherosclerosis through mouse-human comparative genetics

Susceptibility to atherosclerosis is determined by both environmental and genetic factors. Its genetic determinants have been studied by use of quantitative-trait-locus (QTL) analysis. So far, 21 atherosclerosis QTLs have been identified in the mouse: 7 in a high-fat-diet model only, 9 in a sensitized model (apolipoprotein E- or LDL [low-density lipoprotein] receptor-deficient mice) only, and 5 in both models, suggesting that different gene sets operate in each model and that a subset operates in both. Among the 27 human atherosclerosis QTLs reported, 17 (63%) are located in regions homologous (concordant) to mouse QTLs, suggesting that these mouse and human atherosclerosis QTLs have the same underlying genes. Therefore, genes regulating human atherosclerosis will be found most efficiently by first finding their orthologs in concordant mouse QTLs. Novel mouse QTL genes will be found most efficiently by using a combination of the following strategies: identifying QTLs in new crosses performed with previously unused parental strains; inducing mutations in large-scale, high-throughput mutagenesis screens; and using new genomic and bioinformatics tools. Once QTL genes are identified in mice, they can be tested in human association studies for their relevance in human atherosclerotic disease.