Prospective associations of coronary heart disease loci in African Americans using the MetaboChip: the PAGE study

BACKGROUND

Coronary heart disease (CHD) is a leading cause of morbidity and mortality in African Americans. However, there is a paucity of studies assessing genetic determinants of CHD in African Americans. We examined the association of published variants in CHD loci with incident CHD, attempted to fine map these loci, and characterize novel variants influencing CHD risk in African Americans.

METHODS AND RESULTS

Up to 8,201 African Americans (including 546 first CHD events) were genotyped using the MetaboChip array in the Atherosclerosis Risk in Communities (ARIC) study and Women's Health Initiative (WHI). We tested associations using Cox proportional hazard models in sex- and study-stratified analyses and combined results using meta-analysis. Among 44 validated CHD loci available in the array, we replicated and fine-mapped the SORT1 locus, and showed same direction of effects as reported in studies of individuals of European ancestry for SNPs in 22 additional published loci. We also identified a SNP achieving array wide significance (MYC: rs2070583, allele frequency 0.02, P = 8.1 × 10(-8)), but the association did not replicate in an additional 8,059 African Americans (577 events) from the WHI, HealthABC and GeneSTAR studies, and in a meta-analysis of 5 cohort studies of European ancestry (24,024 individuals including 1,570 cases of MI and 2,406 cases of CHD) from the CHARGE Consortium.

CONCLUSIONS

Our findings suggest that some CHD loci previously identified in individuals of European ancestry may be relevant to incident CHD in African Americans.

Trans-ethnic meta-analysis of white blood cell phenotypes

White blood cell (WBC) count is a common clinical measure used as a predictor of certain aspects of human health, including immunity and infection status. WBC count is also a complex trait that varies among individuals and ancestry groups. Differences in linkage disequilibrium structure and heterogeneity in allelic effects are expected to play a role in the associations observed between populations. Prior genome-wide association study (GWAS) meta-analyses have identified genomic loci associated with WBC and its subtypes, but much of the heritability of these phenotypes remains unexplained. Using GWAS summary statistics for over 50 000 individuals from three diverse populations (Japanese, African-American and European ancestry), a Bayesian model methodology was employed to account for heterogeneity between ancestry groups. This approach was used to perform a trans-ethnic meta-analysis of total WBC, neutrophil and monocyte counts. Ten previously known associations were replicated and six new loci were identified, including several regions harboring genes related to inflammation and immune cell function. Ninety-five percent credible interval regions were calculated to narrow the association signals and fine-map the putatively causal variants within loci. Finally, a conditional analysis was performed on the most significant SNPs identified by the trans-ethnic meta-analysis (MA), and nine secondary signals within loci previously associated with WBC or its subtypes were identified. This work illustrates the potential of trans-ethnic analysis and ascribes a critical role to multi-ethnic cohorts and consortia in exploring complex phenotypes with respect to variants that lie outside the European-biased GWAS pool.

Pleiotropic genes for metabolic syndrome and inflammation

Metabolic syndrome (MetS) has become a health and financial burden worldwide. The MetS definition captures clustering of risk factors that predict higher risk for diabetes mellitus and cardiovascular disease. Our study hypothesis is that additional to genes influencing individual MetS risk factors, genetic variants exist that influence MetS and inflammatory markers forming a predisposing MetS genetic network. To test this hypothesis a staged approach was undertaken. (a) We analyzed 17 metabolic and inflammatory traits in more than 85,500 participants from 14 large epidemiological studies within the Cross Consortia Pleiotropy Group. Individuals classified with MetS (NCEP definition), versus those without, showed on average significantly different levels for most inflammatory markers studied. (b) Paired average correlations between 8 metabolic traits and 9 inflammatory markers from the same studies as above, estimated with two methods, and factor analyses on large simulated data, helped in identifying 8 combinations of traits for follow-up in meta-analyses, out of 130,305 possible combinations between metabolic traits and inflammatory markers studied. (c) We performed correlated meta-analyses for 8 metabolic traits and 6 inflammatory markers by using existing GWAS published genetic summary results, with about 2.5 million SNPs from twelve predominantly largest GWAS consortia. These analyses yielded 130 unique SNPs/genes with pleiotropic associations (a SNP/gene associating at least one metabolic trait and one inflammatory marker). Of them twenty-five variants (seven loci newly reported) are proposed as MetS candidates. They map to genes MACF1, KIAA0754, GCKR, GRB14, COBLL1, LOC646736-IRS1, SLC39A8, NELFE, SKIV2L, STK19, TFAP2B, BAZ1B, BCL7B, TBL2, MLXIPL, LPL, TRIB1, ATXN2, HECTD4, PTPN11, ZNF664, PDXDC1, FTO, MC4R and TOMM40. Based on large data evidence, we conclude that inflammation is a feature of MetS and several gene variants show pleiotropic genetic associations across phenotypes and might explain a part of MetS correlated genetic architecture. These findings warrant further functional investigation.

Meta-analysis of genome-wide association studies in African Americans provides insights into the genetic architecture of type 2 diabetes

Type 2 diabetes (T2D) is more prevalent in African Americans than in Europeans. However, little is known about the genetic risk in African Americans despite the recent identification of more than 70 T2D loci primarily by genome-wide association studies (GWAS) in individuals of European ancestry. In order to investigate the genetic architecture of T2D in African Americans, the MEta-analysis of type 2 DIabetes in African Americans (MEDIA) Consortium examined 17 GWAS on T2D comprising 8,284 cases and 15,543 controls in African Americans in stage 1 analysis. Single nucleotide polymorphisms (SNPs) association analysis was conducted in each study under the additive model after adjustment for age, sex, study site, and principal components. Meta-analysis of approximately 2.6 million genotyped and imputed SNPs in all studies was conducted using an inverse variance-weighted fixed effect model. Replications were performed to follow up 21 loci in up to 6,061 cases and 5,483 controls in African Americans, and 8,130 cases and 38,987 controls of European ancestry. We identified three known loci (TCF7L2, HMGA2 and KCNQ1) and two novel loci (HLA-B and INS-IGF2) at genome-wide significance (4.15 × 10(-94) Collapse

Key Words Collapse

MESH Headings

• Black or African American/genetics
• Diabetes Mellitus, Type 2/genetics
• Diabetes Mellitus, Type 2/pathology
• Genome-Wide Association Study
• HLA-B27 Antigen/genetics
• HMGA2 Protein/genetics
• Humans
• KCNQ1 Potassium Channel/genetics
• Mutant Chimeric Proteins/genetics
• Polymorphism, Single Nucleotide
• Transcription Factor 7-Like 2 Protein/genetics

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Greater collagen-induced platelet aggregation following cyclooxygenase 1 inhibition predicts incident acute coronary syndromes

Greater ex vivo platelet aggregation to agonists may identify individuals at risk of acute coronary syndromes (ACS). However, increased aggregation to a specific agonist may be masked by inherent variability in other activation pathways. In this study, we inhibited the cyclooxygenase-1 (COX1) pathway with 2-week aspirin therapy and measured residual aggregation to collagen and ADP to determine whether increased aggregation in a non-COX1 pathway is associated with incident ACS. We assessed ex vivo whole blood platelet aggregation in 1,699 healthy individuals with a family history of early-onset coronary artery disease followed for 6±1.2 years. Incident ACS events were observed in 22 subjects. Baseline aggregation was not associated with ACS. After COX1 pathway inhibition, collagen-induced aggregation was significantly greater in participants with ACS compared with those without (29.0 vs. 23.6 ohms, p < 0.001). In Cox proportional hazards models, this association remained significant after adjusting for traditional cardiovascular risk factors (HR = 1.10, 95%CI = 1.06-1.15; p < 0.001). In contrast, ADP-induced aggregation after COX1 inhibition was not associated with ACS. After COX1 pathway inhibition, subjects with greater collagen-induced platelet aggregation demonstrated a significant excess risk of incident ACS. These data suggest that platelet activation related to collagen may play an important role in the risk of ACS.

Abstract 264: High Serum Lp(a) Levels Are Associated With Subclinical 3-Vessel and Left Main Coronary Disease, Severe Stenoses and Plaque Volume in Apparently Healthy African Americans

Background: Serum Lp(a) is a CAD risk factor in European Americans (EA). Levels are 2-3 fold higher in African Americans (AA) but associations with CAD are inconsistent, including coronary calcium. The relationship of race-specific levels of Lp(a) with the extent and severity of subclinical total coronary plaque (TCP) has not been described.

Methods: We screened 418 apparently healthy individuals for risk factors and coronary plaque using advanced CTA. TCP volumes (mm3) were quantified using a validated automated method. Lp(a) was measured by ELISA. The association of Lp(a) with plaque was investigated by race. Multivariable modeling was performed with adjustment for traditional CAD risk factors, including LDL-C, and intrafamilial correlations.

Results: Mean age was 51±11 years; 57% female; 34% AA. Lp(a) was higher in AA than in EA (median 38 [18,65] vs 17 [10,33], p<0.0001). Plaque was present in 45% of AA and 47% of EA. In those with plaque continuous Lp(a) levels were associated with plaque volume in AA (β=8.83, p<0.0001) but not EA (β=1.49, p=0.45). Lp(a) was strongly associated with plaque extent and severity (Table), and with TCP volume in AA (adjusted p=0.01) but not in EA (p=0.10). In AA, Lp(a)≥60 mg/dL (top quintile) was independently associated with a 3.7 times greater risk of 3-vessel and/or LM disease (95% CI:1.4-10.3), a 6.6 times greater risk of having a stenosis ≥50% (95% CI:1.4-38.4, p=0.02), and higher TCP (median 438 [203,1247] vs 142 [73,262], p=0.001).

Conclusion: High Lp(a) is strongly associated with coronary plaque extent, severity, and volume in apparently healthy AA. High levels of Lp(a) may be particularly important in the pathogenesis of CAD in AA.

Abstract 536: RNA-Seq Identifies Differential Expression of Platelet Transcripts Between People With Hyper- and Hypoaggregation to Collagen

Background: Platelet aggregation plays an important role in the pathogenesis of myocardial infarction, and high platelet aggregability is associated with increased risk of events. We hypothesized that inter-individual variability in platelet function is associated with differences in the mRNA transcripts found in platelets from hyper-aggregators and hypo-aggregators.

Methods: Eight African American (discovery cohort) and four European American (validation cohort) males with family history of early onset coronary artery disease were enrolled. Individuals were divided into hyper- and hypo-aggregators based on maximal aggregation to collagen using whole blood impedance aggregometry. RNA was extracted from leukocyte-depleted platelet-rich plasma and approximately 70 million 100bp paired-end reads per sample were obtained using an Illumina HiSeq 2500. RNA-seq analysis was performed using Bowtie/TopHat/Cufflinks software pipeline. Genes with expression ≥ 1 fragments per kilobase of transcript per million reads (FPKM) were considered to be expressed. On log2 scale, ≥ 2-fold (discovery cohort) and ≥ 1-fold (replication cohort) change in gene expression were considered to be significantly differentially expressed.

Results: Among the 9,373 expressed genes, the most highly expressed nonubiquitous genes included GP1BB, GP9, PPBP, PF4, & TUBB1, confirming our methods. Hyper-aggregability was associated with up-regulation of 239 genes and down-regulation of 29 genes in the discovery cohort (44 and 2 replicated in validation cohort respectively). Pathway analysis found that genes related to sphingosine-1P3 (such as RHOA [ras homolog family member A], GNAZ [G protein, alpha z polypeptide], VEGFA [vascular endothelial growth factor A]) and platelet aggregation pathways (such as GP9 [platelet glycoprotein IX], TLN1 [talin 1], ITGB3 [platelet glycoprotein IIIa]) were up-regulated in hyper-aggregators.

Conclusion: RNA-seq and pathway analyses found that hyper- and hypo-aggregators have significant differences in gene expression. Increased expression of sphingosine-1P3 and platelet aggregation pathway genes in hyper-aggregators highlights the relationship of signal transduction with increased platelet aggregation.

Extreme deep white matter hyperintensity volumes are associated with African American race

BACKGROUND

African Americans (AAs) have a higher prevalence of extreme ischemic white matter hyperintensities (WMHs) on magnetic resonance imaging (MRI) than do European Americans (EAs) based on the Cardiovascular Health Study (CHS) score. Ischemic white matter disease, limited to the deep white matter, may be biologically distinct from disease in other regions and may reflect a previously observed trend toward an increased risk of subcortical lacunar infarcts in AAs. We hypothesized that extreme deep WMH volume (DWMV) or periventricular volume (PV) may also have a higher prevalence in AAs. Thus, we studied extreme CHS scores and extreme DWMV and PV in a healthy population enriched for cardiovascular disease risk factors.

METHODS

We imaged the brains of 593 subjects who were first-degree relatives of probands with early onset coronary disease prior to 60 years of age. WMHs were manually delineated on 3-tesla cranial MRI by a trained radiology reader; the location and volume of lesions were characterized using automated software. DWMV and PV were measured directly with automated software, and the CHS score was determined by a neuroradiologist. Volumes were characterized as being in the upper 25% versus lower 75% of total lesion volume. Volumes in the upper versus the remaining quartiles were examined for AA versus EA race using multiple logistic regression (generalized estimating equations adjusted for family relatedness) and adjusted for major vascular disease risk factors including age ≥55 years versus <55, sex, current smoking, obesity, hypertension, diabetes and low-density lipoprotein >160 mg/dl.

RESULTS

Participants were 58% women and 37% AAs, with a mean age of 51.5 ± 11.0 years (range, 29-74 years). AAs had significantly higher odds of having extreme DWMVs (odds ratio, OR, 1.8; 95% confidence interval, CI, 1.2-2.9; p = 0.0076) independently of age, sex, hypertension and all other risk factors. AAs also had significantly higher odds of having extreme CHS scores ≥3 (OR, 1.3; 95% CI, 1.1-3.6; p = 0.025). Extreme PV was not significantly associated with AA race (OR, 1.3; 95% CI, 0.81-2.1; p = 0.26).

CONCLUSIONS

AAs from families with early-onset cardiovascular disease are more likely to have extreme DWMVs (a subclinical form of cerebrovascular disease) and an extreme CHS score, but not extreme PV, independently of age and other cardiovascular disease risk factors. These findings suggest that this AA population is at an increased risk for DWMV and may be at an increased risk for future subcortical stroke. Longitudinal studies are required to see if DWMV is predictive of symptomatic subcortical strokes in this population.

A Simple Scalable Association Hypothesis Test Combining Gene-wide Evidence From Multiple Polymorphisms

AIMS

In single-nucleotide polymorphism (SNP) scans, SNP-phenotype association hypotheses are tested, however there is biological interpretation only for genes that span multiple SNPs. We demonstrate and validate a method of combining gene-wide evidence using data for high-density lipoprotein cholesterol (HDLC).

METHODOLOGY

In a family based study (N=1782 from 482 families), we used 1000 phenotype-permuted datasets to determine the correlation of z-test statistics for 592 SNP-HDLC association tests comprising 14 genes previously reported to be associated with HDLC. We generated gene-wide p-values using the distribution of the sum of correlated z-statistics.

RESULTS

Of the 14 genes, CETP was significant (p=4.0×10^-5 <0.05/14), while PLTP was significant at the borderline (p=6.7×10^-3 <0.1/14). These p-values were confirmed using empirical distributions of the sum of χ² association statistics as a gold standard (2.9×10^-6 and 1.8×10^-3, respectively). Genewide p-values were more significant than Bonferroni-corrected p-value for the most significant SNP in 11 of 14 genes (p=0.023). Genewide p-values calculated from SNP correlations derived for 20 simulated normally distributed phenotypes reproduced those derived from the 1000 phenotype-permuted datasets were correlated with the empirical distributions (Spearman correlation = 0.92 for both).

CONCLUSION

We have validated a simple scalable method to combine polymorphism-level evidence into gene-wide statistical evidence. High-throughput gene-wide hypothesis tests may be used in biologically interpretable genomewide association scans. Genewide association tests may be used to meaningfully replicate findings in populations with different linkage disequilibrium structure, when SNP-level replication is not expected.

Noncalcified coronary plaque volumes in healthy people with a family history of early onset coronary artery disease

BACKGROUND

Although age and sex distributions of calcified coronary plaque have been well described in the general population, noncalcified plaque (NCP) distributions remain unknown. This is important because NCP is a putative precursor for clinical coronary artery disease and could serve as a sentinel for aggressive primary prevention, especially in high-risk populations. We examined the distributions of NCP and calcified coronary plaque in healthy 30- to 74-year-old individuals from families with early onset coronary artery disease.

METHODS AND RESULTS

Participants in the GeneSTAR family study (N=805), mean age 51.1±10.8 years, 56% women, were screened for coronary artery disease risk factors and coronary plaque using dual-source computed tomographic angiography. Plaque volumes (mm(3)) were quantified using a validated automated method. The prevalence of coronary plaque was 57.8% in men and 35.8% in women (P<0.0001). NCP volume increased with age (P<0.001) and was higher in men than women (P<0.001). Although NCP, as a percentage of total plaque, was inversely related to age (P<0.01), NCP accounted for most of the total plaque volume at all ages, especially in men and women <55 years (>70% and >80%, respectively). Higher Framingham risk was associated with the number of affected vessels (P<0.01), but 44% of men and 20.8% of women considered intermediate risk had left main and 3-vessel disease involvement.

CONCLUSIONS

The majority of coronary plaque was noncalcified, particularly in younger individuals. These findings support the importance of assessing family history and suggest that early primary prevention interventions may be warranted at younger ages in families with early onset coronary artery disease.

Genome-wide association study for circulating tissue plasminogen activator levels and functional follow-up implicates endothelial STXBP5 and STX2

OBJECTIVE

Tissue plasminogen activator (tPA), a serine protease, catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for endogenous fibrinolysis. In some populations, elevated plasma levels of tPA have been associated with myocardial infarction and other cardiovascular diseases. We conducted a meta-analysis of genome-wide association studies to identify novel correlates of circulating levels of tPA.

APPROACH AND RESULTS

Fourteen cohort studies with tPA measures (N=26 929) contributed to the meta-analysis. Three loci were significantly associated with circulating tPA levels (P<5.0×10(-8)). The first locus is on 6q24.3, with the lead single nucleotide polymorphism (SNP; rs9399599; P=2.9×10(-14)) within STXBP5. The second locus is on 8p11.21. The lead SNP (rs3136739; P=1.3×10(-9)) is intronic to POLB and <200 kb away from the tPA encoding the gene PLAT. We identified a nonsynonymous SNP (rs2020921) in modest linkage disequilibrium with rs3136739 (r(2)=0.50) within exon 5 of PLAT (P=2.0×10(-8)). The third locus is on 12q24.33, with the lead SNP (rs7301826; P=1.0×10(-9)) within intron 7 of STX2. We further found evidence for the association of lead SNPs in STXBP5 and STX2 with expression levels of the respective transcripts. In in vitro cell studies, silencing STXBP5 decreased the release of tPA from vascular endothelial cells, whereas silencing STX2 increased the tPA release. Through an in silico lookup, we found no associations of the 3 lead SNPs with coronary artery disease or stroke.

CONCLUSIONS

We identified 3 loci associated with circulating tPA levels, the PLAT region, STXBP5, and STX2. Our functional studies implicate a novel role for STXBP5 and STX2 in regulating tPA release.

Abstract 43: Increased Activation of Inflammatory Genes in Monocytes of Healthy People with Ischemic White Matter Disease

Introduction: White matter hyperintensities (WMH) on MRI represent small vessel ischemic cerebrovascular disease. Greater WMH burden is associated with higher levels of circulating inflammatory cytokines in persons > 65 years with dementia, suggesting a pro-inflammatory vascular process. We hypothesized that middle-aged, asymptomatic, apparently healthy high risk people with high WMH burden would demonstrate increased inflammatory gene expression in monocytes analyzed with microarray.

Methods: Subjects (N=70) were identified from a larger MRI study in 593 healthy family members of persons with early-onset CAD (< 60 years). We obtained monocytes and examined gene expression in all subjects (mean age 58.1 ± 10 years, range 30-73; 55% female; 36% African American). These included 35 subjects with the greatest WMH burden using volumetric methods in the larger study, and 35 unrelated age-sex-race matched controls with the lowest WMH burden. Monocyte mRNA was analyzed on Illumina Human HT12 v4 microarrays. We performed unsupervised principal component analysis (PCA) followed by ANOVA between high and low WMH groups. Genes with 2 SD differences in expression between groups were included for Gene Ontology permutation analysis using 1000 permutations within “GoMiner”. Only genes with the lowest false discovery rate (FDR) were summarized.

Results: PCA identified no significant clustering. A total of 1,315 genes were included in gene ontology analysis and resulted in 10 ontological categories with an FDR<0.01%. This included 164 genes all showing greater expression in the high WMH group. These were key inflammatory genes, such as tumor necrosis factor (TNF), interleukin-6 (IL-6), interleukin-8 (IL-8), toll like receptor 5 and 7 (TLR5, TLR7) and integrin alpha 5 and M (ITGA5, ITGAM).

Conclusions: Gene microarray ontological analysis of monocytes in healthy middle aged high risk people with greater WMH burden shows increased activation of genes of known innate inflammatory pathways. These findings likely reflect greater pro-inflammatory processes in persons with greater WMH, consistent with the presence of inflammation-mediated occult small vessel cerebrovascular disease in a healthy middle-aged population at increased risk for vascular diseases.

Abstract 109: Manipulative Dexterity is Associated with Occult White Matter Ischemic Lesions in Healthy Asymptomatic Persons at Increased Risk for Cardiovascular Disease

Introduction: Persons with a family history of early-onset coronary artery disease (CAD) have an excess risk of stroke and CAD. White matter lesions (WML) on MRI represent small vessel ischemic cerebrovascular disease and are associated with incident stroke and neurocognitive decline with age. We hypothesized manipulative manual dexterity, an integration of fine motor, visual spatial, and cognition function, may be affected by increased WML burden in task-relevant brain regions across age ranges in persons at risk for pre-clinical occult vascular disease. We tested this in a large population with a family history of early CAD.

Methods: Healthy 29-74 year old subjects (N=714; mean age 51± 11 years; mean education 14 ± 3 years; 42% male, 38% Black) were identified from probands with CAD <60 years. WML location and volumes were measured on 3T FLAIR MRI. Manipulative manual dexterity was measured with standardized timed grooved pegboard test. Left and right pegboard scores were averaged.

Results: WML were observed in all age groups; mean overall pegboard scores were 108±18, and were within reference norms. In unadjusted analysis, pegboard scores were highly correlated in the expected direction with total WML volumes, r=0.34, p=<.0001; subcortical volumes r=0.30, <.0001 periventricular volumes r=0.31, <.0001; and with most regional WML volumes; frontal 0.34, <.0001; insula r=0.31, p<.0001, parietal r=0.31, p<.0001, and temporal volumes r=0.17, p <.0001. In separate multivariate regression analyses predicting (log) pegboard score adjusted for age, sex, race, education and nonindependence of families (GEE), total WML volume became more statistically significant ( p=5.79E-05) while other regions retained statistical significance, p< 0.01.

Conclusions: Our findings in a large population-based sample with a family history of early CAD confirm that greater WML volumes in multiple brain locations are associated with higher pegboard scores (worse performance) independent of age, sex, race, and education. This suggests that small vessel cerebrovascular disease is present in an early preclinical state and that WML volumes impact manipulative manual dexterity in healthy middle-aged and younger individuals with excess risk for clinical vascular disease.

Abstract 110: Age Associated Brain Volume is More Closely Correlated to Periventricular than Deep White Matter Disease

Introduction: The loss of total brain volume (TBV) due to aging is associated with increasing ischemic white matter lesion volume (WMH) and dementia. Lower TBV may be secondary to chronic ischemia and hypoperfusion throughout the periventricular white matter rather than the burden of focal ischemia in the deep white matter. We hypothesized lower TBV would be more closely correlated with increasing periventricular white matter lesion volume (PV) rather than deep white matter lesion volume (DWMH).

Methods: We enrolled 593 asymptomatic family members of probands with premature coronary artery disease (<60 years). DWMH, PV, and TBV were measured with 3Tesla MRI. Multivariate regression was completed for DWMH, PV, and TBV using volume change per age decade controlling for sex, race, diabetes, smoking currently, hypertension, obesity , and intracranial volume (ICV) for TBV, and a spline incorporated at age 54.

Results: Participants were 58% women, 37% African-American, 29-74 years old. TBV/ICV was more correlated to PV than DWMH (correlation coefficients -0.26 and -0.11, p=<0.001 and 0.006). The PV was greater with older age 9%/decade until age 54 (95% CI 4-15%) and 24%/decade after age 54 (95% CI 1.6-3.2%). TBV was reduced with older age: 1.1 % smaller/decade until age 54 (95% CI -0.6 to -1.6) and 2.4% smaller/decade after (95% CI -1.6 to -3.1). For PV and TBV their age association changed significantly after age 54 (p=0.012, and 0.014). DWMH age association remained constant regardless of age.

Conclusions: PV is more strongly correlated to TBV than DWMH and the age associated changes in PV and TBV were more similar to one another than DWMH. The association of increasing PV with lower TBV may help to explain the association of cognitive and motor decline with increasing PV. Future longitudinal studies are needed to verify this association.

Effect of positive well-being on incidence of symptomatic coronary artery disease

Although negative emotions and psychiatric morbidity have often been found to increase incident coronary artery disease (CAD) risk, fewer studies have shown positive emotions to be protective against CAD; none have been performed in high-risk healthy populations, taking risk factors into account. Thus, we examined the effect of positive well-being on incident CAD in both a high-risk initially healthy population and a national probability sample. We screened healthy siblings of probands with documented early-onset CAD from 1985 to 2007 in the GeneSTAR (Genetic Study of Atherosclerosis Risk) population and examined sociodemographic data, risk factors, and positive well-being using the General Well-Being Schedule. We further classified siblings into high-, intermediate-, and low-risk strata according to the Framingham risk score and followed them for 5 to 25 years. Siblings (n = 1,483) with greater baseline General Well-Being Schedule total scores were significantly less likely to develop CAD (hazard ratio 0.67, 95% confidence interval 0.58 to 0.79), independent of age, gender, race, and traditional risk factors. Protection was strongest in the high Framingham risk score stratum (hazard ratio 0.52, 95% confidence interval 0.30 to 0.90). The findings were replicated in the first National Health and Nutrition Examination Survey and Epidemiologic Follow-up Study (n = 5,992; hazard ratio 0.87, 95% confidence interval 0.83 to 0.93). In conclusion, positive well-being was associated with nearly a 1/3 reduction in CAD in a high-risk population with a positive family history, a nearly 50% reduction in incident CAD in the highest risk stratum in those with a positive family history, and a 13% reduction in incident CAD in a national probability sample, independent of the traditional CAD risk factors.

Multiethnic meta-analysis of genome-wide association studies in >100 000 subjects identifies 23 fibrinogen-associated Loci but no strong evidence of a causal association between circulating fibrinogen and cardiovascular disease

BACKGROUND

Estimates of the heritability of plasma fibrinogen concentration, an established predictor of cardiovascular disease, range from 34% to 50%. Genetic variants so far identified by genome-wide association studies explain only a small proportion (<2%) of its variation.

METHODS AND RESULTS

We conducted a meta-analysis of 28 genome-wide association studies including >90 000 subjects of European ancestry, the first genome-wide association meta-analysis of fibrinogen levels in 7 studies in blacks totaling 8289 samples, and a genome-wide association study in Hispanics totaling 1366 samples. Evaluation for association of single-nucleotide polymorphisms with clinical outcomes included a total of 40 695 cases and 85 582 controls for coronary artery disease, 4752 cases and 24 030 controls for stroke, and 3208 cases and 46 167 controls for venous thromboembolism. Overall, we identified 24 genome-wide significant (P<5×10(-8)) independent signals in 23 loci, including 15 novel associations, together accounting for 3.7% of plasma fibrinogen variation. Gene-set enrichment analysis highlighted key roles in fibrinogen regulation for the 3 structural fibrinogen genes and pathways related to inflammation, adipocytokines, and thyrotrophin-releasing hormone signaling. Whereas lead single-nucleotide polymorphisms in a few loci were significantly associated with coronary artery disease, the combined effect of all 24 fibrinogen-associated lead single-nucleotide polymorphisms was not significant for coronary artery disease, stroke, or venous thromboembolism.

CONCLUSIONS

We identify 23 robustly associated fibrinogen loci, 15 of which are new. Clinical outcome analysis of these loci does not support a causal relationship between circulating levels of fibrinogen and coronary artery disease, stroke, or venous thromboembolism.

Relation of subclinical coronary artery atherosclerosis to cerebral white matter disease in healthy subjects from families with early-onset coronary artery disease

White matter disease (WMD) of the brain is associated with incident stroke. Similarly, subclinical calcified coronary artery plaque has been associated with incident coronary artery disease (CAD) events. Although atherogenesis in both vascular beds may share some common mechanisms, the extent to which subclinical CAD is associated with WMD across age ranges in subjects with a family history of early-onset CAD remains unknown. We screened 405 apparently healthy participants in the Genetic Study of Atherosclerotic Risk for CAD risk factors and for the presence of noncalcified and calcified coronary plaque using dual-source multidetector cardiac computed tomographic angiography. The presence and volumes of WMD were assessed by 3-Tesla brain magnetic resonance imaging. Participants were 60% women, 36% African-American, mean age 51.6 ± 10.6 years. The overall prevalence of coronary plaque was 43.0%. Subjects with coronary plaque had significantly greater WMD volumes (median 1,222 mm³, interquartile range 448 to 3,871) compared with those without coronary plaque (median 551 mm³, interquartile range 105 to 1,523, p <0.001). In multivariate regression analysis, adjusting for age, gender, race, traditional risk factors, total brain volume, and intrafamilial correlations, the presence of coronary plaque was independently associated with WMD volume (p = 0.05). This study shows a significant association between WMD and noncalcified and calcified coronary plaque in healthy subjects, independent of age and risk factors. In conclusion, these findings support the premise of possible shared causal pathways in 2 vascular beds in families at increased risk for early-onset vascular disease.

Genome-wide association analysis of blood-pressure traits in African-ancestry individuals reveals common associated genes in African and non-African populations

High blood pressure (BP) is more prevalent and contributes to more severe manifestations of cardiovascular disease (CVD) in African Americans than in any other United States ethnic group. Several small African-ancestry (AA) BP genome-wide association studies (GWASs) have been published, but their findings have failed to replicate to date. We report on a large AA BP GWAS meta-analysis that includes 29,378 individuals from 19 discovery cohorts and subsequent replication in additional samples of AA (n = 10,386), European ancestry (EA) (n = 69,395), and East Asian ancestry (n = 19,601). Five loci (EVX1-HOXA, ULK4, RSPO3, PLEKHG1, and SOX6) reached genome-wide significance (p < 1.0 × 10(-8)) for either systolic or diastolic BP in a transethnic meta-analysis after correction for multiple testing. Three of these BP loci (EVX1-HOXA, RSPO3, and PLEKHG1) lack previous associations with BP. We also identified one independent signal in a known BP locus (SOX6) and provide evidence for fine mapping in four additional validated BP loci. We also demonstrate that validated EA BP GWAS loci, considered jointly, show significant effects in AA samples. Consequently, these findings suggest that BP loci might have universal effects across studied populations, demonstrating that multiethnic samples are an essential component in identifying, fine mapping, and understanding their trait variability.

Genome-wide association of body fat distribution in African ancestry populations suggests new loci

Central obesity, measured by waist circumference (WC) or waist-hip ratio (WHR), is a marker of body fat distribution. Although obesity disproportionately affects minority populations, few studies have conducted genome-wide association study (GWAS) of fat distribution among those of predominantly African ancestry (AA). We performed GWAS of WC and WHR, adjusted and unadjusted for BMI, in up to 33,591 and 27,350 AA individuals, respectively. We identified loci associated with fat distribution in AA individuals using meta-analyses of GWA results for WC and WHR (stage 1). Overall, 25 SNPs with single genomic control (GC)-corrected p-values<5.0 × 10(-6) were followed-up (stage 2) in AA with WC and with WHR. Additionally, we interrogated genomic regions of previously identified European ancestry (EA) WHR loci among AA. In joint analysis of association results including both Stage 1 and 2 cohorts, 2 SNPs demonstrated association, rs2075064 at LHX2, p = 2.24×10(-8) for WC-adjusted-for-BMI, and rs6931262 at RREB1, p = 2.48×10(-8) for WHR-adjusted-for-BMI. However, neither signal was genome-wide significant after double GC-correction (LHX2: p = 6.5 × 10(-8); RREB1: p = 5.7 × 10(-8)). Six of fourteen previously reported loci for waist in EA populations were significant (p<0.05 divided by the number of independent SNPs within the region) in AA studied here (TBX15-WARS2, GRB14, ADAMTS9, LY86, RSPO3, ITPR2-SSPN). Further, we observed associations with metabolic traits: rs13389219 at GRB14 associated with HDL-cholesterol, triglycerides, and fasting insulin, and rs13060013 at ADAMTS9 with HDL-cholesterol and fasting insulin. Finally, we observed nominal evidence for sexual dimorphism, with stronger results in AA women at the GRB14 locus (p for interaction = 0.02). In conclusion, we identified two suggestive loci associated with fat distribution in AA populations in addition to confirming 6 loci previously identified in populations of EA. These findings reinforce the concept that there are fat distribution loci that are independent of generalized adiposity.

Genetics of coronary artery calcification among African Americans, a meta-analysis

Background

Coronary heart disease (CHD) is the major cause of death in the United States. Coronary artery calcification (CAC) scores are independent predictors of CHD. African Americans (AA) have higher rates of CHD but are less well-studied in genomic studies. We assembled the largest AA data resource currently available with measured CAC to identify associated genetic variants.

Methods

We analyzed log transformed CAC quantity (ln(CAC + 1)), for association with ~2.5 million single nucleotide polymorphisms (SNPs) and performed an inverse-variance weighted meta-analysis on results for 5,823 AA from 8 studies. Heritability was calculated using family studies. The most significant SNPs among AAs were evaluated in European Ancestry (EA) CAC data; conversely, the significance of published SNPs for CAC/CHD in EA was queried within our AA meta-analysis.

Results

Heritability of CAC was lower in AA (~30%) than previously reported for EA (~50%). No SNP reached genome wide significance (p < 5E-08). Of 67 SNPs with p < 1E-05 in AA there was no evidence of association in EA CAC data. Four SNPs in regions previously implicated in CAC/CHD (at 9p21 and PHACTR1) in EA reached nominal significance for CAC in AA, with concordant direction. Among AA, rs16905644 (p = 4.08E-05) had the strongest association in the 9p21 region.

Conclusions

While we observed substantial heritability for CAC in AA, we failed to identify loci for CAC at genome-wide significant levels despite having adequate power to detect alleles with moderate to large effects. Although suggestive signals in AA were apparent at 9p21 and additional CAC and CAD EA loci, overall the data suggest that even larger samples and an ethnic specific focus will be required for GWAS discoveries for CAC in AA populations.

Genome-wide association analysis of red blood cell traits in African Americans: the COGENT Network

Laboratory red blood cell (RBC) measurements are clinically important, heritable and differ among ethnic groups. To identify genetic variants that contribute to RBC phenotypes in African Americans (AAs), we conducted a genome-wide association study in up to ~16 500 AAs. The alpha-globin locus on chromosome 16pter [lead SNP rs13335629 in ITFG3 gene; P < 1E-13 for hemoglobin (Hgb), RBC count, mean corpuscular volume (MCV), MCH and MCHC] and the G6PD locus on Xq28 [lead SNP rs1050828; P < 1E - 13 for Hgb, hematocrit (Hct), MCV, RBC count and red cell distribution width (RDW)] were each associated with multiple RBC traits. At the alpha-globin region, both the common African 3.7 kb deletion and common single nucleotide polymorphisms (SNPs) appear to contribute independently to RBC phenotypes among AAs. In the 2p21 region, we identified a novel variant of PRKCE distinctly associated with Hct in AAs. In a genome-wide admixture mapping scan, local European ancestry at the 6p22 region containing HFE and LRRC16A was associated with higher Hgb. LRRC16A has been previously associated with the platelet count and mean platelet volume in AAs, but not with Hgb. Finally, we extended to AAs the findings of association of erythrocyte traits with several loci previously reported in Europeans and/or Asians, including CD164 and HBS1L-MYB. In summary, this large-scale genome-wide analysis in AAs has extended the importance of several RBC-associated genetic loci to AAs and identified allelic heterogeneity and pleiotropy at several previously known genetic loci associated with blood cell traits in AAs.

A meta-analysis identifies new loci associated with body mass index in individuals of African ancestry

Genome-wide association studies (GWAS) have identified 36 loci associated with body mass index (BMI), predominantly in populations of European ancestry. We conducted a meta-analysis to examine the association of >3.2 million SNPs with BMI in 39,144 men and women of African ancestry and followed up the most significant associations in an additional 32,268 individuals of African ancestry. We identified one new locus at 5q33 (GALNT10, rs7708584, P = 3.4 × 10(-11)) and another at 7p15 when we included data from the GIANT consortium (MIR148A-NFE2L3, rs10261878, P = 1.2 × 10(-10)). We also found suggestive evidence of an association at a third locus at 6q16 in the African-ancestry sample (KLHL32, rs974417, P = 6.9 × 10(-8)). Thirty-two of the 36 previously established BMI variants showed directionally consistent effect estimates in our GWAS (binomial P = 9.7 × 10(-7)), five of which reached genome-wide significance. These findings provide strong support for shared BMI loci across populations, as well as for the utility of studying ancestrally diverse populations.

Targeted deep resequencing identifies coding variants in the PEAR1 gene that play a role in platelet aggregation

Platelet aggregation is heritable, and genome-wide association studies have detected strong associations with a common intronic variant of the platelet endothelial aggregation receptor1 (PEAR1) gene both in African American and European American individuals. In this study, we used a sequencing approach to identify additional exonic variants in PEAR1 that may also determine variability in platelet aggregation in the GeneSTAR Study. A 0.3 Mb targeted region on chromosome 1q23.1 including the entire PEAR1 gene was Sanger sequenced in 104 subjects (45% male, 49% African American, age = 52±13) selected on the basis of hyper- and hypo- aggregation across three different agonists (collagen, epinephrine, and adenosine diphosphate). Single-variant and multi-variant burden tests for association were performed. Of the 235 variants identified through sequencing, 61 were novel, and three of these were missense variants. More rare variants (MAF<5%) were noted in African Americans compared to European Americans (108 vs. 45). The common intronic GWAS-identified variant (rs12041331) demonstrated the most significant association signal in African Americans (p = 4.020×10(-4)); no association was seen for additional exonic variants in this group. In contrast, multi-variant burden tests indicated that exonic variants play a more significant role in European Americans (p = 0.0099 for the collective coding variants compared to p = 0.0565 for intronic variant rs12041331). Imputation of the individual exonic variants in the rest of the GeneSTAR European American cohort (N = 1,965) supports the results noted in the sequenced discovery sample: p = 3.56×10(-4), 2.27×10(-7), 5.20×10(-5) for coding synonymous variant rs56260937 and collagen, epinephrine and adenosine diphosphate induced platelet aggregation, respectively. Sequencing approaches confirm that a common intronic variant has the strongest association with platelet aggregation in African Americans, and show that exonic variants play an additional role in platelet aggregation in European Americans.

Gene-centric meta-analysis of lipid traits in African, East Asian and Hispanic populations

Meta-analyses of European populations has successfully identified genetic variants in over 100 loci associated with lipid levels, but our knowledge in other ethnicities remains limited. To address this, we performed dense genotyping of ∼2,000 candidate genes in 7,657 African Americans, 1,315 Hispanics and 841 East Asians, using the IBC array, a custom ∼50,000 SNP genotyping array. Meta-analyses confirmed 16 lipid loci previously established in European populations at genome-wide significance level, and found multiple independent association signals within these lipid loci. Initial discovery and in silico follow-up in 7,000 additional African American samples, confirmed two novel loci: rs5030359 within ICAM1 is associated with total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) (p = 8.8×10(-7) and p = 1.5×10(-6) respectively) and a nonsense mutation rs3211938 within CD36 is associated with high-density lipoprotein cholesterol (HDL-C) levels (p = 13.5×10(-12)). The rs3211938-G allele, which is nearly absent in European and Asian populations, has been previously found to be associated with CD36 deficiency and shows a signature of selection in Africans and African Americans. Finally, we have evaluated the effect of SNPs established in European populations on lipid levels in multi-ethnic populations and show that most known lipid association signals span across ethnicities. However, differences between populations, especially differences in allele frequency, can be leveraged to identify novel signals, as shown by the discovery of ICAM1 and CD36 in the current report.

Genome-wide association study for circulating levels of PAI-1 provides novel insights into its regulation

We conducted a genome-wide association study to identify novel associations between genetic variants and circulating plasminogen activator inhibitor-1 (PAI-1) concentration, and examined functional implications of variants and genes that were discovered. A discovery meta-analysis was performed in 19 599 subjects, followed by replication analysis of genome-wide significant (P < 5 × 10(-8)) single nucleotide polymorphisms (SNPs) in 10 796 independent samples. We further examined associations with type 2 diabetes and coronary artery disease, assessed the functional significance of the SNPs for gene expression in human tissues, and conducted RNA-silencing experiments for one novel association. We confirmed the association of the 4G/5G proxy SNP rs2227631 in the promoter region of SERPINE1 (7q22.1) and discovered genome-wide significant associations at 3 additional loci: chromosome 7q22.1 close to SERPINE1 (rs6976053, discovery P = 3.4 × 10(-10)); chromosome 11p15.2 within ARNTL (rs6486122, discovery P = 3.0 × 10(-8)); and chromosome 3p25.2 within PPARG (rs11128603, discovery P = 2.9 × 10(-8)). Replication was achieved for the 7q22.1 and 11p15.2 loci. There was nominal association with type 2 diabetes and coronary artery disease at ARNTL (P < .05). Functional studies identified MUC3 as a candidate gene for the second association signal on 7q22.1. In summary, SNPs in SERPINE1 and ARNTL and an SNP associated with the expression of MUC3 were robustly associated with circulating levels of PAI-1.