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- Burgess, S., et al.
(author)
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Bayesian methods for meta-analysis of causal relationships estimated using genetic instrumental variables
- 2010
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In: Statistics in medicine. - : Wiley. - 1097-0258 .- 0277-6715. ; 29:12, s. 1298-311
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Journal article (peer-reviewed)abstract
- Genetic markers can be used as instrumental variables, in an analogous way to randomization in a clinical trial, to estimate the causal relationship between a phenotype and an outcome variable. Our purpose is to extend the existing methods for such Mendelian randomization studies to the context of multiple genetic markers measured in multiple studies, based on the analysis of individual participant data. First, for a single genetic marker in one study, we show that the usual ratio of coefficients approach can be reformulated as a regression with heterogeneous error in the explanatory variable. This can be implemented using a Bayesian approach, which is next extended to include multiple genetic markers. We then propose a hierarchical model for undertaking a meta-analysis of multiple studies, in which it is not necessary that the same genetic markers are measured in each study. This provides an overall estimate of the causal relationship between the phenotype and the outcome, and an assessment of its heterogeneity across studies. As an example, we estimate the causal relationship of blood concentrations of C-reactive protein on fibrinogen levels using data from 11 studies. These methods provide a flexible framework for efficient estimation of causal relationships derived from multiple studies. Issues discussed include weak instrument bias, analysis of binary outcome data such as disease risk, missing genetic data, and the use of haplotypes.
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- Sarwar, Nadeem, et al.
(author)
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Interleukin-6 receptor pathways in coronary heart disease : a collaborative meta-analysis of 82 studies
- 2012
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In: The Lancet. - New York, NY, USA : Elsevier. - 0140-6736 .- 1474-547X. ; 379:9822, s. 1205-1213
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Journal article (peer-reviewed)abstract
- Background: Persistent inflammation has been proposed to contribute to various stages in the pathogenesis of cardiovascular disease. Interleukin-6 receptor (IL6R) signalling propagates downstream inflammation cascades. To assess whether this pathway is causally relevant to coronary heart disease, we studied a functional genetic variant known to affect IL6R signalling. Methods: In a collaborative meta-analysis, we studied Asp358Ala (rs2228145) in IL6R in relation to a panel of conventional risk factors and inflammation biomarkers in 125 222 participants. We also compared the frequency of Asp358Ala in 51 441 patients with coronary heart disease and in 136 226 controls. To gain insight into possible mechanisms, we assessed Asp358Ala in relation to localised gene expression and to postlipopolysaccharide stimulation of interleukin 6. Findings: The minor allele frequency of Asp358Ala was 39%. Asp358Ala was not associated with lipid concentrations, blood pressure, adiposity, dysglycaemia, or smoking (p value for association per minor allele >= 0.04 for each). By contrast, for every copy of 358Ala inherited, mean concentration of IL6R increased by 34.3% (95% CI 30.4-38.2) and of interleukin 6 by 14.6% (10.7-18.4), and mean concentration of C-reactive protein was reduced by 7.5% (5.9-9.1) and of fibrinogen by 1.0% (0.7-1.3). For every copy of 358Ala inherited, risk of coronary heart disease was reduced by 3.4% (1.8-5.0). Asp358Ala was not related to IL6R mRNA levels or interleukin-6 production in monocytes. Interpretation: Large-scale human genetic and biomarker data are consistent with a causal association between IL6R-related pathways and coronary heart disease.
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- Stolte, W. C., et al.
(author)
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Inner-shell photoionization of atomic chlorine
- 2013
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 88:5
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Journal article (peer-reviewed)abstract
- Relative partial cross sections have been measured following photoexcitation of atomic chlorine near the Cl 2p and Cl 1s ionization thresholds. In addition, Breit-Pauli R-matrix calculations have been carried out in the region of the 2p thresholds, and the results are compared with experiment. Owing to angular-momentum considerations, it was found that the resonances associated with the higher 2p(-1) thresholds should be significantly wider than the lower ones, and this is borne out in both the experimental and the theoretical results. It is shown that a large number of resonance series contribute to the cross section, which make it difficult to untangle, and suggestions for further work to better understand the spectra are presented.
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