Ruth Frikke-Schmidt

Remnant cholesterol as a causal risk factor for ischemic heart disease.

OBJECTIVES The aim of this study was to test the hypothesis that elevated nonfasting remnant cholesterol is a causal risk factor for ischemic heart disease independent of reduced high-density lipoprotein (HDL) cholesterol. BACKGROUND Elevated remnant cholesterol is associated with elevated levels of triglyceride-rich lipoproteins and with reduced HDL cholesterol, and all are associated with ischemic heart disease. METHODS A total of 73,513 subjects from Copenhagen were genotyped, of whom 11,984 had ischemic heart disease diagnosed between 1976 and 2010. Fifteen genetic variants were selected, affecting: 1) nonfasting remnant cholesterol alone; 2) nonfasting remnant cholesterol and HDL cholesterol combined; 3) HDL cholesterol alone; or 4) low-density lipoprotein (LDL) cholesterol alone as a positive control. The variants were used in a Mendelian randomization design. RESULTS The causal odds ratio for a 1 mmol/l (39 mg/dl) genetic increase of nonfasting remnant cholesterol was 2.8 (95% confidence interval [CI]: 1.9 to 4.2), with a corresponding observational hazard ratio of 1.4 (95% CI: 1.3 to 1.5). For the ratio of nonfasting remnant cholesterol to HDL cholesterol, corresponding values were 2.9 (95% CI: 1.9 to 4.6) causal and 1.2 (95% CI 1.2 to 1.3) observational for a 1-U increase. However, for HDL cholesterol, corresponding values were 0.7 (95% CI: 0.4 to 1.4) causal and 1.6 (95% CI: 1.4 to 1.7) observational for a 1 mmol/l (39 mg/dl) decrease. Finally, for LDL cholesterol, corresponding values were 1.5 (95% CI: 1.3 to 1.6) causal and 1.1 (95% CI: 1.1 to 1.2) observational for a 1 mmol/l (39 mg/dl) increase. CONCLUSIONS A nonfasting remnant cholesterol increase of 1 mmol/l (39 mg/dl) is associated with a 2.8-fold causal risk for ischemic heart disease, independent of reduced HDL cholesterol. This implies that elevated cholesterol content of triglyceride-rich lipoprotein particles causes ischemic heart disease. However, because pleiotropic effects of the genetic variants studied cannot be totally excluded, these findings need to be confirmed using additional genetic variants and/or randomized intervention trials.

Genetic variation in ABC transporter A1 contributes to HDL cholesterol in the general population

Homozygosity for mutations in ABC transporter A1 (ABCA1) causes Tangier disease, a rare HDL-deficiency syndrome. Whether heterozygosity for genetic variation in ABCA1 also contributes to HDL cholesterol (HDL-C) levels in the general population is presently unclear. We determined whether mutations or single-nucleotide polymorphisms (SNPs) in ABCA1 were overrepresented in individuals with the lowest 1% (n=95) or highest 1% (n=95) HDL-C levels in the general population by screening the core promoter and coding region of ABCA1. For all nonsynonymous SNPs identified, we determined the effect of genotype on lipid traits in 9,259 individuals from the general population. Heterozygosity for ABCA1 mutations was identified in 10% of individuals with low HDL-C only. Three of 6 nonsynonymous SNPs (V771M, V825I, and R1587K) were associated with increases or decreases in HDL-C in women in the general population and some with consistent trends in men, determined as isolated single-site effects varying only at the relevant SNP. Finally, these results were consistent over time. In conclusion, we show that at least 10% of individuals with low HDL-C in the general population are heterozygous for mutations in ABCA1 and that both mutations and SNPs in ABCA1 contribute to HDL-C levels in the general population.

LCAT, HDL Cholesterol and Ischemic Cardiovascular Disease: A Mendelian Randomization Study of HDL Cholesterol in 54,500 Individuals

BACKGROUND Epidemiologically, high-density lipoprotein (HDL) cholesterol levels associate inversely with risk of ischemic cardiovascular disease. Whether this is a causal relation is unclear. METHODS We studied 10,281 participants in the Copenhagen City Heart Study (CCHS) and 50,523 participants in the Copenhagen General Population Study (CGPS), of which 991 and 1,693 participants, respectively, had developed myocardial infarction (MI) by August 2010. Participants in the CCHS were genotyped for all six variants identified by resequencing lecithin-cholesterol acyltransferase in 380 individuals. One variant, S208T (rs4986970, allele frequency 4%), associated with HDL cholesterol levels in both the CCHS and the CGPS was used to study causality of HDL cholesterol using instrumental variable analysis. RESULTS Epidemiologically, in the CCHS, a 13% (0.21 mmol/liter) decrease in plasma HDL cholesterol levels was associated with an 18% increase in risk of MI. S208T associated with a 13% (0.21 mmol/liter) decrease in HDL cholesterol levels but not with increased risk of MI or other ischemic end points. The causal odds ratio for MI for a 50% reduction in plasma HDL cholesterol due to S208T genotype in both studies combined was 0.49 (0.11-2.16), whereas the hazard ratio for MI for a 50% reduction in plasma HDL cholesterol in the CCHS was 2.11 (1.70-2.62) (P(comparison) = 0.03). CONCLUSION Low plasma HDL cholesterol levels robustly associated with increased risk of MI but genetically decreased HDL cholesterol did not. This may suggest that low HDL cholesterol levels per se do not cause MI.

Genetically elevated non-fasting triglycerides and calculated remnant cholesterol as causal risk factors for myocardial infarction

AIMS Elevated non-fasting triglycerides mark elevated levels of remnant cholesterol. Using a Mendelian randomization approach, we tested whether genetically increased remnant cholesterol in hypertriglyceridaemia due to genetic variation in the apolipoprotein A5 gene (APOA5) associates with an increased risk of myocardial infarction (MI). METHODS AND RESULTS We resequenced the core promoter and coding regions of APOA5 in individuals with the lowest 1% (n = 95) and highest 2% (n = 190) triglyceride levels in the Copenhagen City Heart Study (CCHS, n = 10 391). Genetic variants which differed in frequency between the two extreme triglyceride groups (c.-1131T > C, S19W, and c.*31C > T; P-value: 0.06 to <0.001), thus suggesting an effect on triglyceride levels, were genotyped in the Copenhagen General Population Study (CGPS), the CCHS, and the Copenhagen Ischemic Heart Disease Study (CIHDS), comprising a total of 5705 MI cases and 54 408 controls. Genotype combinations of these common variants associated with increases in non-fasting triglycerides and calculated remnant cholesterol of, respectively, up to 68% (1.10 mmol/L) and 56% (0.40 mmol/L) (P < 0.001), and with a corresponding odds ratio for MI of 1.87 (95% confidence interval: 1.25-2.81). Using APOA5 genotypes in instrumental variable analysis, the observational hazard ratio for a doubling in non-fasting triglycerides was 1.57 (1.32-2.68) compared with a causal genetic odds ratio of 1.94 (1.40-1.85) (P for comparison = 0.28). For calculated remnant cholesterol, the corresponding values were 1.67(1.38-2.02) observational and 2.23(1.48-3.35) causal (P for comparison = 0.21). CONCLUSION These data are consistent with a causal association between elevated levels of remnant cholesterol in hypertriglyceridaemia and an increased risk of MI. Limitations include that remnants were not measured directly, and that APOA5 genetic variants may influence other lipoprotein parameters.

Genetic Variation in ABCA1 Predicts Ischemic Heart Disease in the General Population

Objective—We tested the hypothesis that 6 nonsynonymous single nucleotide polymorphisms (SNPs) in ATP-Binding-Cassette transporter A1 (ABCA1) affect risk of ischemic heart disease (IHD) in the general population. Methods and Results—We genotyped 9259 individuals from the Danish general population followed for 25 years. Two SNPs (V771M and V825I) were previously associated with increases in HDL-C, 1 (R1587K) with decreased HDL-C, whereas 3 (R219K, I883M and E1172D) did not affect HDL-C levels. Despite this, 5 out of 6 SNPs (V771M, V825I, I883M, E1172D, R1587K) predicted increased risk of IHD. Similar results were obtained in a verification sample with 932 IHD cases versus 7999 controls. A stepwise regression approach identified V771M, I883M, and E1172D as the most important predictors of IHD and additive effects on IHD risk were present for V771M/I883M and I883M/E1172D pairs. Conclusions—We show that 3 of 6 nonsynonymous SNPs in ABCA1 predict risk of IHD in the general population.

Genetic inhibition of CETP, ischemic vascular disease and mortality, and possible adverse effects.

OBJECTIVES This study tested whether genetic variation in the CETP gene is consistent with a protective effect of cholesteryl ester transfer protein (CETP) inhibition on risk of ischemic events and on total mortality, without the adverse effects reported for torcetrapib. BACKGROUND Torcetrapib, an inhibitor of CETP, increased risk of death and ischemic cardiovascular disease of those randomized to the drug, despite improving the lipid profile. METHODS The Copenhagen City Heart Study is a prospective cohort study of 10,261 individuals, aged 20 to 93 years, who were followed for up to 34 years (1976 to 2010). Of these, 2,087 developed ischemic heart disease, 1,064 developed ischemic cerebrovascular disease, and 3,807 died during follow-up. We selected 2 common genetic variants in CETP previously associated with reductions in CETP activity, thus mimicking the effect of pharmacological CETP inhibition. RESULTS In individuals carrying 4 versus 0 high-density lipoprotein cholesterol-increasing alleles, there was an increase in levels of high-density lipoprotein cholesterol of up to 14% (0.2 mmol/l), and concomitant decreases in triglycerides, low-density lipoprotein cholesterol, and non-high-density lipoprotein cholesterol of, respectively, 6% (0.1 mmol/l), 3% (0.1 mmol/l), and 4% (0.2 mmol/l) (p for trend 0.004 to <0.001). Corresponding hazard ratios were 0.76 (95% confidence interval [CI]: 0.68 to 0.85) for any ischemic vascular event, 0.74 (95% CI: 0.65 to 0.85) for ischemic heart disease, 0.65 (95% CI: 0.54 to 0.79) for myocardial infarction, 0.77 (95% CI: 0.65 to 0.93) for ischemic cerebrovascular disease, 0.71 (95% CI: 0.58 to 0.88) for ischemic stroke, and 0.88 (95% CI: 0.80 to 0.97) for total mortality. CETP genotypes did not associate with variation in markers of possible side effects previously reported for torcetrapib. CONCLUSIONS Genetic CETP inhibition associates with reductions in risk of ischemic heart disease, myocardial infarction, ischemic cerebrovascular disease, and ischemic stroke, with a corresponding antiatherogenic lipid profile, and with increased longevity, without adverse effects.

Genome-Wide Association Analysis of High-Density Lipoprotein Cholesterol in the Population-Based KORA Study Sheds New Light on Intergenic Regions

Background—High-density lipoprotein cholesterol (HDLC) is a strong risk factor for atherosclerosis and is assumed to be under considerable genetic control. We aimed to identify gene regions that influence HDLC levels by a genome-wide association analysis in the population-based KORA (Cooperative Health Research in the Region of Augsburg) study. Methods and Results—In KORA S3/F3 (n=1643), we analyzed 377 865 quality-checked single-nucleotide polymorphisms (SNPs; 500K, Affymetrix, Santa Clara, Calif), complemented by the publicly available genome-wide association results from the Diabetes Genetics Initiative (n=2631) and by replication data from KORA S4 (n=4037) and the Copenhagen City Heart Study (n=9205). Among the 13 SNPs selected from the KORA S3/F3 500K probability value list, 3 showed consistent associations in subsequent replications: 1 SNP 10 kb upstream of CETP (pooled probability value=8.5×10−27), 1 SNP approximately 40 kb downstream of LIPG (probability value=4.67×10−10), both independent of previously reported SNPs, and 1 from an already reported region of LPL (probability value=2.82×10−11). Bioinformatical analyses indicate a potential functional relevance of the respective SNPs. Conclusions—The present genome-wide association study identified 2 interesting HDLC-relevant regions upstream of CETP and downstream of LIPG. This draws attention to the importance of long-range effects of intergenic regions, which have been underestimated so far, and may impact future candidate-gene–association studies toward extending the region analyzed. Furthermore, the present study reinforced CETP and LPL as HDLC genes and thereby underscores the power of this type of genome-wide association approach to pinpoint associations of common polymorphisms with effects explaining as little as 0.5% of the HDLC variance in the general population.

Low-Density Lipoprotein Cholesterol and the Risk of Cancer: A Mendelian Randomization Study

BACKGROUND Low plasma levels of low-density lipoprotein (LDL) cholesterol are associated with an increased risk of cancer, but whether this association is causal is unclear. METHODS We studied 10 613 participants in the Copenhagen City Heart Study (CCHS) and 59 566 participants in the Copenhagen General Population Study, 6816 of whom had developed cancer by May 2009. Individuals were genotyped for PCSK9 R46L (rs11591147), ABCG8 D19H (rs11887534), and APOE R112C (rs429358) and R158C (rs7412) polymorphisms, all of which are associated with lifelong reduced plasma LDL cholesterol levels. Plasma LDL cholesterol was calculated using the Friedewald equation in samples in which the triglyceride level was less than 354 mg/dL and measured directly by colorimetry for samples with higher triglyceride levels. Risk of cancer was estimated prospectively using Cox proportional hazards regression analyses and cross-sectionally by logistic regression analyses. Causality was studied using instrumental variable analysis. All statistical tests were two-sided. RESULTS In the CCHS, compared with plasma LDL cholesterol levels greater than the 66th percentile (>158 mg/dL), those lower than the 10th percentile (< 87 mg/dL) were associated with a 43% increase (95% confidence interval [CI] = 15% to 79% increase) in the risk of cancer. The polymorphisms were associated with up to a 38% reduction (95% CI = 36% to 41% reduction) in LDL cholesterol levels but not with increased risk of cancer. The causal odds ratio for cancer for a 50% reduction in plasma LDL cholesterol level due to all the genotypes in both studies combined was 0.96 (95% CI = 0.87 to 1.05), whereas the hazard ratio of cancer for a 50% reduction in plasma LDL cholesterol level in the CCHS was 1.10 (95% CI = 1.01 to 1.21) (P for causal odds ratio vs observed hazard ratio = .03). CONCLUSION Low plasma LDL cholesterol levels were robustly associated with an increased risk of cancer, but genetically decreased LDL cholesterol was not. This finding suggests that low LDL cholesterol levels per se do not cause cancer.

Elevated Plasma YKL-40 Predicts Increased Risk of Gastrointestinal Cancer and Decreased Survival After Any Cancer Diagnosis in the General Population

PURPOSE Elevated plasma YKL-40 is a biomarker of poor prognosis in cancer patients. We tested the hypotheses that elevated plasma YKL-40 predicts risk of cancer as well as survival after a cancer diagnosis in the general population. PATIENTS AND METHODS A prospective cohort study of 8,899 subjects (20 to 95 years) from the Danish general population, the Copenhagen City Heart Study, observed for 11 years for cancer incidence and 14 years for death: 1,432 participants had a first incident cancer, 968 of these died. Hazard ratios (HRs) for cancer events and death after events according to plasma YKL-40 in sex and 10 years age percentile categories: 0% to 33%, 34% to 66%, 67% to 90%, 91% to 95%, and 96% to 100%. RESULTS The cumulative incidence of gastrointestinal cancer increased with increasing YKL-40 (trend P < .0001). Multifactorially adjusted HRs for gastrointestinal cancer were 1.0 (95% CI, 0.7 to 1.5) for YKL-40 in category 34% to 66%, 1.5 for 67% to 90% (95% CI, 1.0 to 2.3), 2.4 for 91% to 95%, (95% CI, 1.3 to 4.6), and 3.4 for 96% to 100% (95% CI, 1.9 to 6.1) versus YKL-40 category 0% to 33% (P < .0001). Participants with any cancer event and YKL-40 category 91% to 100% had a median survival time after the diagnosis of 1 year versus 4 years in participants with YKL-40 category 0% to 33% (P < .0001). Corresponding values for gastrointestinal cancer were 6 months versus 1 year (P = .007). Multifactorially adjusted HRs for early death were 1.8 (95% CI, 1.3 to 2.5; P < .0001) after any cancer and 2.4 (95% CI, 1.3 to 4.3; P = .005) after gastrointestinal cancer in participants with YKL-40 category 91% to 100% versus 0% to 33%. CONCLUSION In the general population, elevated plasma YKL-40 predicts increased risk of gastrointestinal cancer and decreased survival after any cancer diagnosis.

Apolipoprotein E genotype, cardiovascular biomarkers and risk of stroke : Systematic review and meta-analysis of 14 015 stroke cases and pooled analysis of primary biomarker data from up to 60 883 individuals

BACKGROUND At the APOE gene, encoding apolipoprotein E, genotypes of the ε2/ε3/ε4 alleles associated with higher LDL-cholesterol (LDL-C) levels are also associated with higher coronary risk. However, the association of APOE genotype with other cardiovascular biomarkers and risk of ischaemic stroke is less clear. We evaluated the association of APOE genotype with risk of ischaemic stroke and assessed whether the observed effect was consistent with the effects of APOE genotype on LDL-C or other lipids and biomarkers of cardiovascular risk. METHODS We conducted a systematic review of published and unpublished studies reporting on APOE genotype and ischaemic stroke. We pooled 41 studies (with a total of 9027 cases and 61,730 controls) using a Bayesian meta-analysis to calculate the odds ratios (ORs) for ischaemic stroke with APOE genotype. To better evaluate potential mechanisms for any observed effect, we also conducted a pooled analysis of primary data using 16 studies (up to 60,883 individuals) of European ancestry. We evaluated the association of APOE genotype with lipids, other circulating biomarkers of cardiovascular risk and carotid intima-media thickness (C-IMT). RESULTS The ORs for association of APOE genotypes with ischaemic stroke were: 1.09 (95% credible intervals (CrI): 0.84-1.43) for ε2/ε2; 0.85 (95% CrI: 0.78-0.92) for ε2/ε3; 1.05 (95% CrI: 0.89-1.24) for ε2/ε4; 1.05 (95% CrI: 0.99-1.12) for ε3/ε4; and 1.12 (95% CrI: 0.94-1.33) for ε4/ε4 using the ε3/ε3 genotype as the reference group. A regression analysis that investigated the effect of LDL-C (using APOE as the instrument) on ischaemic stroke showed a positive dose-response association with an OR of 1.33 (95% CrI: 1.17, 1.52) per 1 mmol/l increase in LDL-C. In the separate pooled analysis, APOE genotype was linearly and positively associated with levels of LDL-C (P-trend: 2 × 10(-152)), apolipoprotein B (P-trend: 8.7 × 10(-06)) and C-IMT (P-trend: 0.001), and negatively and linearly associated with apolipoprotein E (P-trend: 6 × 10(-26)) and HDL-C (P-trend: 1.6 × 10(-12)). Associations with lipoprotein(a), C-reactive protein and triglycerides were non-linear. CONCLUSIONS In people of European ancestry, APOE genotype showed a positive dose-response association with LDL-C, C-IMT and ischaemic stroke. However, the association of APOE ε2/ε2 genotype with ischaemic stroke requires further investigation. This cross-domain concordance supports a causal role of LDL-C on ischaemic stroke.