Christiane L. Haase

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 Apolipoprotein A-I, High-Density Lipoprotein Cholesterol Levels, and Risk of Ischemic Heart Disease

CONTEXT Epidemiologically, levels of high-density lipoprotein (HDL) cholesterol and its major protein constituent, apolipoprotein A-I (apoA-I), are inversely related to risk of ischemic heart disease (IHD). OBJECTIVE We tested whether common genetic variation in the apolipoprotein A1 gene (APOA1) contributes to apoA-I and HDL cholesterol levels and risk of IHD in the general population. DESIGN We resequenced the regulatory and coding regions of APOA1 in 190 individuals from the Copenhagen City Heart Study with the lowest 1% (n=95) and highest 1% (n=95) apoA-I levels. Two single-nucleotide polymorphisms (SNPs) were subsequently genotyped in the Copenhagen City Heart Study (n=10,273) and in 2361 cases with IHD (the Copenhagen Ischemic Heart Disease Study). RESULTS In total, 13 genetic variants were identified. Three SNPs, g.-560A→C, g.-151C→T, and *181A→G, determined a haplotype that differed between high and low apoA-I groups (6 vs. 1%, P=0.002). Genotype combinations of two SNPs, the g.-560A→C (tagging the g.-560A→C/g.-151C→T/*181A→G haplotype) and g.-310G→A (situated near a potential functional promoter site), were associated with increases in apoA-I and HDL cholesterol levels of up to 6.6 and 8.5%, respectively, resulting in theoretically predicted reductions in risk of 9 and 8% for IHD and 14 and 12% for myocardial infarction (MI). Despite this, these same genotype combinations were not associated with decreased risk of IHD or MI. CONCLUSION Common genetic variation in APOA1 associated with increased apoA-I and HDL cholesterol levels did not associate with decreased risk of IHD or MI.

HDL Cholesterol and Risk of Type 2 Diabetes: A Mendelian Randomization Study.

Observationally, low levels of HDL cholesterol are consistently associated with increased risk of type 2 diabetes. Therefore, plasma HDL cholesterol increasing has been suggested as a novel therapeutic option to reduce the risk of type 2 diabetes. Whether levels of HDL cholesterol are causally associated with type 2 diabetes is unknown. In a prospective study of the general population (n = 47,627), we tested whether HDL cholesterol–related genetic variants were associated with low HDL cholesterol levels and, in turn, with an increased risk of type 2 diabetes. HDL cholesterol–decreasing gene scores and allele numbers associated with up to −13 and −20% reductions in HDL cholesterol levels. The corresponding theoretically predicted hazard ratios for type 2 diabetes were 1.44 (95% CI 1.38–1.52) and 1.77 (1.61–1.95), whereas the genetic estimates were nonsignificant. Genetic risk ratios for type 2 diabetes for a 0.2 mmol/L reduction in HDL cholesterol were 0.91 (0.75–1.09) and 0.93 (0.78–1.11) for HDL cholesterol–decreasing gene scores and allele numbers, respectively, compared with the corresponding observational hazard ratio of 1.37 (1.32–1.42). In conclusion, genetically reduced HDL cholesterol does not associate with increased risk of type 2 diabetes, suggesting that the corresponding observational association is due to confounding and/or reverse causation.

Mutation in APOA1 predicts increased risk of ischaemic heart disease and total mortality without low HDL cholesterol levels.

Abstract.  Haase CL, Frikke‐Schmidt R, Nordestgaard BG, Kateifides AK, Kardassis D, Nielsen LB, Andersen CB, Køber L, Johnsen AH, Grande P, Zannis VI, Tybjærg‐Hansen A (Copenhagen University Hospitals and Faculty of Health Sciences, University of Copenhagen, Denmark; University of Crete Medical School, Heraklion, Greece; Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA, USA). Mutation in APOA1 predicts increased risk of ischaemic heart disease and total mortality without low HDL cholesterol levels. J Intern Med 2011; 270: 136–146.

Population-Based Resequencing of APOA1 in 10,330 Individuals: Spectrum of Genetic Variation, Phenotype, and Comparison with Extreme Phenotype Approach

Rare genetic variants, identified by in-detail resequencing of loci, may contribute to complex traits. We used the apolipoprotein A-I gene (APOA1), a major high-density lipoprotein (HDL) gene, and population-based resequencing to determine the spectrum of genetic variants, the phenotypic characteristics of these variants, and how these results compared with results based on resequencing only the extremes of the apolipoprotein A-I (apoA-I) distribution. First, we resequenced APOA1 in 10,330 population-based participants in the Copenhagen City Heart Study. The spectrum and distribution of genetic variants was determined as a function of the number of individuals resequenced. Second, apoA-I and HDL cholesterol phenotypes were determined for nonsynonymous (NS) and synonymous (S) variants and were validated in the Copenhagen General Population Study (n = 45,239). Third, observed phenotypes were compared with those predicted using an extreme phenotype approach based on the apoA-I distribution. Our results are as follows: First, population-based resequencing of APOA1 identified 40 variants of which only 7 (18%) had minor allele frequencies >1%, and most were exceedingly rare. Second, 0.27% of individuals in the general population were heterozygous for NS variants which were associated with substantial reductions in apoA-I (up to 39 mg/dL) and/or HDL cholesterol (up to 0.9 mmol/L) and, surprisingly, 0.41% were heterozygous for variants predisposing to amyloidosis. NS variants associated with a hazard ratio of 1.72 (1.09–2.70) for myocardial infarction (MI), largely driven by A164S, a variant not associated with apoA-I or HDL cholesterol levels. Third, using the extreme apoA-I phenotype approach, NS variants correctly predicted the apoA-I phenotype observed in the population-based resequencing. However, using the extreme approach, between 79% (screening 0–1st percentile) and 21% (screening 0–20th percentile) of all variants were not identified; among these were variants previously associated with amyloidosis. Population-based resequencing of APOA1 identified a majority of rare NS variants associated with reduced apoA-1 and HDL cholesterol levels and/or predisposing to amyloidosis. In addition, NS variants associated with increased risk of MI.

Heterozygosity for R1141X in ABCC6 and risk of ischemic vascular disease.

Background— Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease caused by loss-of-function mutations in ABCC6 and characterized by elastic calcification leading to dermal, ocular, and ischemic vascular disease. We tested the hypothesis that heterozygosity for R1141X, the most frequent PXE-causing mutation in Caucasians, associated with risk of ischemic vascular disease, as previous studies suggested 4- to 11-fold risk of ischemic heart disease (IHD) in heterozygotes. Methods and Results— We studied 10 276 persons from the general population, including 1985 with IHD and 989 with ischemic cerebrovascular disease (ICVD). We examined 45 603 individuals from a cross-sectional general population study, of whom 3738 had IHD and 2335 had ICVD. Finally, we compared 4851 patients with IHD and 625 patients with ICVD with, respectively, 4851 and 625 matched control subjects. We genotyped participants in all studies for ABCC6 R1141X. The frequency of R1141X was 0.6% in all populations studied. ABCC6 R1141X genotype was not associated with an increased risk of IHD, myocardial infarction, ICVD, or ischemic stroke. Furthermore, R1141X genotype did not interact with age on risk of the largest end point, IHD. Finally, R1141X genotype did not associate with variation in plasma levels of high-sensitivity C-reactive protein, fibrinogen, blood pressure, or lipid and lipoproteins in the general population. Conclusions— In 4 studies including 66 831 participants and 13 642 cases with ischemic vascular events, heterozygosity for ABCC6 R1141X did not associate with risk of IHD, myocardial infarction, ICVD, or ischemic stroke.

Subgroups at high risk for ischaemic heart disease:identification and validation in 67 000 individuals from the general population

BACKGROUND The aetiology of ischaemic heart disease (IHD) is complex and is influenced by a spectrum of environmental factors and susceptibility genes. Traditional statistical modelling considers such factors to act independently in an additive manner. The Patient Rule-Induction Method (PRIM) is a multi-model building strategy for evaluating risk attributable to context-dependent gene and environmental effects. METHODS PRIM was applied to 9073 participants from the prospective Copenhagen City Heart Study (CCHS). Gender-specific cumulative incidences were estimated for subgroups defined by categories of age, smoking, hypertension, diabetes, body mass index, total cholesterol, high-density lipoprotein cholesterol and triglycerides and by 94 single nucleotide variants (SNVs).Cumulative incidences for subgroups were validated using an independently ascertained sample of 58 240 participants from the Copenhagen General Population Study (CGPS). RESULTS In the CCHS the overall cumulative incidences were 0.17 in women and 0.21 in men. PRIM identified six and four mutually exclusive subgroups in women and men, respectively, with cumulative incidences of IHD ranging from 0.02 to 0.34. Cumulative incidences of IHD generated by PRIM in the CCHS were validated in four of the six subgroups of women and two of the four subgroups of men in the CGPS. CONCLUSIONS PRIM identified high-risk subgroups characterized by specific contexts of selected values of traditional risk factors and genetic variants. These subgroups were validated in an independently ascertained cohort study. Thus, a multi-model strategy may identify groups of individuals with substantially higher risk of IHD than the overall risk for the general population.