May M. Luke

Identification of Four Gene Variants Associated with Myocardial Infarction

Family history is a major risk factor for myocardial infarction (MI). However, known gene variants associated with MI cannot fully explain the genetic component of MI risk. We hypothesized that a gene-centric association study that was not limited to candidate genes could identify novel genetic associations with MI. We studied 11,053 single-nucleotide polymorphisms (SNPs) in 6,891 genes, focusing on SNPs that could influence gene function to increase the likelihood of identifying disease-causing gene variants. To minimize false-positive associations generated by multiple testing, two studies were used to identify a limited number of nominally associated SNPs; a third study tested the hypotheses that these SNPs are associated with MI. In the initial study (of 340 cases and 346 controls), 637 SNPs were associated with MI (P<.05); these were evaluated in a second study (of 445 cases and 606 controls), and 31 of the 637 SNPs were associated with MI (P<.05) and had the same risk allele as in the first study. For each of these 31 SNPs, we tested the hypothesis that it is associated with MI, using a third study (of 560 cases and 891 controls). We found that four of these gene variants were associated with MI (P<.05; false-discovery rate <10%) and had the same risk allele as in the first two studies. These gene variants encode the cytoskeletal protein palladin (KIAA0992 [odds ratio (OR) 1.40]), a tyrosine kinase (ROS1 [OR 1.75]), and two G protein-coupled receptors (TAS2R50 [OR 1.58] and OR13G1 [OR 1.40]); all ORs are for carriers of two versus zero risk alleles. These findings could lead to a better understanding of MI pathophysiology and improved patient risk assessment.

Association of Gene Variants With Incident Myocardial Infarction in the Cardiovascular Health Study

Objective—We asked whether single nucleotide polymorphisms (SNPs) that had been nominally associated with cardiovascular disease in antecedent studies were also associated with cardiovascular disease in a population-based prospective study of 4522 individuals aged 65 or older. Methods and Results—Based on antecedent studies, we prespecified a risk allele and an inheritance model for each of 74 SNPs. We then tested the association of these SNPs with myocardial infarction (MI) in the Cardiovascular Health Study (CHS). The prespecified risk alleles of 8 SNPs were nominally associated (1-sided P<0.05) with increased risk of MI in White CHS participants. The false discovery rate for these 8 was 0.43, suggesting that about 4 of these 8 are likely to be true positives. The 4 of these 8 SNPs that had the strongest evidence for association with cardiovascular disease before testing in CHS (association in 3 antecedent studies) were in KIF6 (CHS HR=1.29; 90%CI 1.1 to 1.52), VAMP8 (HR=1.2; 90%CI 1.02 to 1.41), TAS2R50 (HR=1.13; 90%CI 1 to 1.27), and LPA (HR=1.62; 90%CI 1.09 to 2.42). Conclusions—Although most of the SNPs investigated were not associated with MI in CHS, evidence from this investigation combined with previous studies suggests that 4 of these SNPs are likely associated with MI.

A Polymorphism in the Protease-Like Domain of Apolipoprotein(a) Is Associated With Severe Coronary Artery Disease

Objectives—The purpose of this study was to identify genetic variants associated with severe coronary artery disease (CAD). Methods and Results—We used 3 case-control studies of white subjects whose severity of CAD was assessed by angiography. The first 2 studies were used to generate hypotheses that were then tested in the third study. We tested 12 077 putative functional single nucleotide polymorphisms (SNPs) in Study 1 (781 cases, 603 controls) and identified 302 SNPs nominally associated with severe CAD. Testing these 302 SNPs in Study 2 (471 cases, 298 controls), we found 5 (in LPA, CALM1, HAP1, AP3B1, and ABCG2) were nominally associated with severe CAD and had the same risk alleles in both studies. We then tested these 5 SNPs in Study 3 (554 cases, 373 controls). We found 1 SNP that was associated with severe CAD: LPA I4399M (rs3798220). LPA encodes apolipoprotein(a), a component of lipoprotein(a). I4399M is located in the protease-like domain of apolipoprotein(a). Compared with noncarriers, carriers of the 4399M risk allele (2.7% of controls) had an adjusted odds ratio for severe CAD of 3.14 (confidence interval 1.51 to 6.56), and had 5-fold higher median plasma lipoprotein(a) levels (P=0.003). Conclusions—The LPA I4399M SNP is associated with severe CAD and plasma lipoprotein(a) levels.

Polymorphism in the apolipoprotein(a) gene, plasma lipoprotein(a), cardiovascular disease, and low-dose aspirin therapy.

OBJECTIVE A minor allele variant (rs3798220) of apolipoprotein(a) has been reported to be associated with elevated plasma lipoprotein(a) [Lp(a)] and increased cardiovascular risk. We investigated whether this allele was associated with elevated Lp(a) and cardiovascular risk in the Womens Health Study, a randomized trial of low-dose aspirin, and whether aspirin reduced cardiovascular risk in minor allele carriers. METHODS AND RESULTS Genotypes of rs3798220 were determined for 25,131 initially healthy Caucasian participants. Median Lp(a) levels at baseline were 10.0, 79.5, and 153.9mg/dL for major allele homozygotes, heterozygotes, and minor allele homozygotes, respectively (P<0.0001). During the 9.9 years of follow-up, minor allele carriers (3.7%) in the placebo group had twofold higher risk of major cardiovascular events than non-carriers (age-adjusted hazard ratio (HR)=2.21, 95% CI: 1.39-3.52). Among carriers, risk was reduced more than twofold by aspirin: for aspirin compared with placebo the age-adjusted HR was 0.44 (95% CI: 0.20-0.94); risk was not significantly reduced among non-carriers (age-adjusted HR=0.91, 95% CI: 0.77-1.08). This interaction between carrier status and aspirin allocation was significant (P=0.048). CONCLUSIONS In the Womens Health Study, carriers of an apolipoprotein(a) variant had elevated Lp(a), doubled cardiovascular risk, and appeared to benefit more from aspirin than non-carriers.

Five common gene variants identify elevated genetic risk for coronary heart disease

Purpose: Because multiple genetic variants influence risk for coronary heart disease, we combined multiple variants that had been associated with coronary heart disease in several studies into a genetic risk score and asked whether a high genetic risk score would be significantly associated with coronary heart disease after accounting for traditional risk factors.Methods: We considered five variants that were associated with coronary heart disease in two studies and confirmed in the Atherosclerosis Risk in Communities study: rs20455 (KIF6), rs3900940 (MYH15), rs7439293 (PALLD), rs2298566 (SNX19), and rs1010 (VAMP8). We calculated a genetic risk score for each Atherosclerosis Risk in Communities study participant and estimated the hazard ratio for incident coronary heart disease of a high genetic risk score (compared with not-high) in Cox models that adjusted for traditional risk factors during a median of 13 years of follow-up.Results: For white participants with a high genetic risk score (4% of the 9129 whites), compared with those without a high genetic risk score, the hazard ratio for incident coronary heart disease was 1.57 (95% confidence interval 1.21–2.04; P = 0.001). Internal validation using bootstrap samples estimated that a hazard ratio of 1.43 could be expected in external populations.Conclusions: After adjusting for traditional risk factors, those with a high genetic risk score had a 57% increased risk of incident coronary heart disease in the Atherosclerosis Risk in Communities study.

Gene Variants of VAMP8 and HNRPUL1 Are Associated With Early-Onset Myocardial Infarction

Objectives—Identify gene variants associated with early-onset myocardial infarction (MI). Methods and Results—We tested 11 647 single-nucleotide polymorphisms (SNPs) for association with early-onset MI in a case-control study (study 1 200 cases, 262 controls). To reduce the number of false positives among the 666 SNPs that were nominally associated with early-onset MI (P<0.05) in study 1, we tested these SNPs in study 2 (434 cases, 504 controls). We found that 8 of the 666 SNPs were associated with early-onset MI in study 2 (P<0.05) and had the same risk alleles as in study 1. These 8 SNPs were then tested for association with early-onset MI in study 3 (187 cases, 434 controls). We found that a VAMP8 variant (P=0.025; odds ratio [OR], 1.75; CI, 1.17 to 2.62) and an HNRPUL1 variant (P=0.0043; OR, 1.92; CI, 1.28 to 2.86) were associated with early-onset MI (nominal P<0.05; false discovery rate <10%) and had the same risk alleles in all 3 studies. Conclusions—Variants in 2 genes were associated with early-onset MI: VAMP8, which is involved in platelet degranulation, and HNRPUL1, which encodes a ribonuclear protein. The identification of these variants could improve understanding of disease mechanisms and suggest novel drug targets.

Genetic Variants in the Apolipoprotein(a) Gene and Coronary Heart Disease

Two independent single-nucleotide polymorphisms (SNPs) in the gene encoding apolipoprotein(a) ( LPA ) have been shown to be associated with coronary heart disease (CHD) and lipoprotein(a) levels in Caucasians. For the missense SNP rs3798220 (Ile4399Met), carriers of 1 or 2 copies of the minor allele (Met) were at 57% increased risk of CHD. For the intronic SNP rs10455872, the risk of CHD increased by 42% for each copy of the minor allele. The rs3798220 SNP was also associated with differential response to aspirin therapy in the Womens Health Study; carriers of the minor allele had a significant reduction in CHD events from aspirin therapy, whereas noncarriers did not have a significant reduction. Lipoprotein(a) [Lp(a)] is a lipoprotein particle that consists of an apolipoprotein(a) [apo(a)] molecule covalently linked by a disulfide bond to the apolipoprotein B-100 (apoB-100) component of a low-density lipoprotein (LDL)-like particle (Figure 1, modified on the Albers et al1 figure). The LPA gene, which encodes apo(a), is thought to have been generated by a duplication of the neighboring plasminogen gene.2 Like the plasminogen protein, the apo(a) has a protease-like domain and multiple kringle domains. Different variants of the LPA gene can affect the plasma level of Lp(a), encode apo(a) size variants (ie, kringle repeat length variations), or both. Figure 1. Apolipoprotein(a) [apo(a)] gene structure and lipoprotein(a) [Lp(a)] particle model. Top panel shows the LPA exons (denoted by vertical boxes) along the 135-kbp genomic region on chromosome 6 (positions 160,872,506 at the right end to 161,007,397 at the left end) and the relative locations of the 2 single-nucleotide polymorphisms and protein domains (based on the HapMap Data Rel28 [http://www.hapmap.org]). Bottom panel depicts an Lp(a) particle that consists of an LDL-like particle, apoB-100, and apo(a) with annotation of the kringle repeats and the Ile4399Met polymorphism (modified on the Albers …

Gene Variants Associated With Ischemic Stroke The Cardiovascular Health Study

Background and Purpose— The purpose of this study was to determine whether 74 single nucleotide polymorphisms (SNPs), which had been associated with coronary heart disease, are associated with incident ischemic stroke. Methods— Based on antecedent studies of coronary heart disease, we prespecified the risk allele for each of the 74 SNPs. We used Cox proportional hazards models that adjusted for traditional risk factors to estimate the associations of these SNPs with incident ischemic stroke during 14 years of follow-up in a population-based study of older adults: the Cardiovascular Health Study (CHS). Results— In white CHS participants, the prespecified risk alleles of 7 of the 74 SNPs (in HPS1, ITGAE, ABCG2, MYH15, FSTL4, CALM1, and BAT2) were nominally associated with increased risk of stroke (one-sided P<0.05, false discovery rate=0.42). In black participants, the prespecified risk alleles of 5 SNPs (in KRT4, LY6G5B, EDG1, DMXL2, and ABCG2) were nominally associated with stroke (one-sided P<0.05, false discovery rate=0.55). The Val12Met SNP in ABCG2 was associated with stroke in both white (hazard ratio, 1.46; 90% CI, 1.05 to 2.03) and black (hazard ratio, 3.59; 90% CI, 1.11 to 11.6) participants of CHS. Kaplan-Meier estimates of the 10-year cumulative incidence of stroke were greater among Val allele homozygotes than among Met allele carriers in both white (10% versus 6%) and black (12% versus 3%) participants of CHS. Conclusions— The Val12Met SNP in ABCG2 (encoding a transporter of sterols and xenobiotics) was associated with incident ischemic stroke in white and black participants of CHS.

Asp92Asn polymorphism in the myeloid IgA Fc receptor is associated with myocardial infarction in two disparate populations: CARE and WOSCOPS.

Objective—Statins reduce inflammation and risk of myocardial infarction (MI). Because the myeloid IgA Fc receptor encoded by FCAR mediates inflammation, we hypothesized that the FCAR Asp92Asn polymorphism is associated with risk of MI and that this risk would be modified by pravastatin. Methods and Results—In the placebo arm of the Cholesterol and Recurrent Events (CARE) study, male carriers of the 92Asn allele had an adjusted hazard ratio for incident MI of 1.68 (95% CI 1.10 to 2.57); relative risk reduction by pravastatin was 69% in carriers and 12% in noncarriers (Pinteraction=0.007). In the placebo arm of the all-male West of Scotland Coronary Prevention Study (WOSCOPS), carriers had an adjusted odds ratio for incident coronary heart disease (CHD) of 1.46 (90% CI 1.05 to 2.03); for pravastatin compared with placebo treatment, the adjusted odds ratios were 0.55 (95% CI 0.32 to 0.93) in carriers and 0.65 (95% CI 0.51 to 0.83) in noncarriers (Pinteraction=0.55). Conclusions—Carriers of 92Asn had increased risk of MI in CARE and increased odds of CHD in WOSCOPS. Pravastatin significantly reduced risk in carriers in both CARE and WOSCOPS. A genotype by treatment interaction was observed in CARE but not in WOSCOPS.

The I4399M variant of apolipoprotein(a) is associated with increased oxidized phospholipids on apolipoprotein B-100 particles.

OBJECTIVES The LPA I4399M (rs3798220) single nucleotide polymorphism (SNP) is associated with increased plasma levels of Lp(a) and advanced coronary artery disease (CAD). We hypothesized that carriers of the Met allele of the I4399M SNP would also have elevated levels of oxidized phospholipids (OxPL) on apoB (OxPL/apoB) particles. METHODS AND RESULTS Plasma levels of Lp(a) and OxPL/apoB were measured in non-carriers (TT genotype, n=116) and carriers (CT/CC genotype, n=58) of the I4399M SNP. Carriers had significantly higher Lp(a) levels [median (interquartile range, IQR)] [43 (9-57)mg/dl vs. 5.5 (2-20)mg/dl, p<0.0001] and smaller apolipoprotein(a) isoforms than non-carriers (number of kringle IV repeats: 18(17-20) vs. 22(18-25), p=0.002). Median (IQR) OxPL/apoB levels were significantly higher in carriers than non-carriers [8019 (6254-31,785) relative light units (RLU) vs. 2168 (1303-5869), p<0.0001]. Patients with small apolipoprotein(a) isoforms had the highest OxPL/apoB levels. The number of kringle IV repeats was inversely related to Lp(a) (r=-0.43, p<0.001) and OxPL/apoB (r=-0.36, p<0.0001) levels. CONCLUSION The CT and CC genotypes of the I4399M SNP in the LPA gene are associated with elevated OxPL/apoB levels, which primarily represent OxPL on Lp(a). The concomitant increase of OxPL/apoB levels in the setting of small apolipoprotein(a) isoforms may potentiate the atherogenic effect on CAD of elevated Lp(a) levels in carriers of the I4399M SNP.