Dataset Information

Homocysteine and coronary heart disease: meta-analysis of MTHFR case-control studies, avoiding publication bias.

ABSTRACT: BACKGROUND:Moderately elevated blood levels of homocysteine are weakly correlated with coronary heart disease (CHD) risk, but causality remains uncertain. When folate levels are low, the TT genotype of the common C677T polymorphism (rs1801133) of the methylene tetrahydrofolate reductase gene (MTHFR) appreciably increases homocysteine levels, so "Mendelian randomization" studies using this variant as an instrumental variable could help test causality. METHODS AND FINDINGS:Nineteen unpublished datasets were obtained (total 48,175 CHD cases and 67,961 controls) in which multiple genetic variants had been measured, including MTHFR C677T. These datasets did not include measurements of blood homocysteine, but homocysteine levels would be expected to be about 20% higher with TT than with CC genotype in the populations studied. In meta-analyses of these unpublished datasets, the case-control CHD odds ratio (OR) and 95% CI comparing TT versus CC homozygotes was 1.02 (0.98-1.07; p?=?0.28) overall, and 1.01 (0.95-1.07) in unsupplemented low-folate populations. By contrast, in a slightly updated meta-analysis of the 86 published studies (28,617 CHD cases and 41,857 controls), the OR was 1.15 (1.09-1.21), significantly discrepant (p?=?0.001) with the OR in the unpublished datasets. Within the meta-analysis of published studies, the OR was 1.12 (1.04-1.21) in the 14 larger studies (those with variance of log OR<0.05; total 13,119 cases) and 1.18 (1.09-1.28) in the 72 smaller ones (total 15,498 cases). CONCLUSIONS:The CI for the overall result from large unpublished datasets shows lifelong moderate homocysteine elevation has little or no effect on CHD. The discrepant overall result from previously published studies reflects publication bias or methodological problems.

SUBMITTER: Clarke R

PROVIDER: S-EPMC3283559 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Homocysteine and coronary heart disease: meta-analysis of MTHFR case-control studies, avoiding publication bias.

Clarke Robert R Bennett Derrick A DA Parish Sarah S Verhoef Petra P Dötsch-Klerk Mariska M Lathrop Mark M Xu Peng P Nordestgaard Børge G BG Holm Hilma H Hopewell Jemma C JC Saleheen Danish D Tanaka Toshihiro T Anand Sonia S SS Chambers John C JC Kleber Marcus E ME Ouwehand Willem H WH Yamada Yoshiji Y Elbers Clara C Peters Bas B Stewart Alexandre F R AF Reilly Muredach M MM Thorand Barbara B Yusuf Salim S Engert James C JC Assimes Themistocles L TL Kooner Jaspal J Danesh John J Watkins Hugh H Samani Nilesh J NJ Collins Rory R Peto Richard R

PLoS medicine 20120221 2

<h4>Background</h4>Moderately elevated blood levels of homocysteine are weakly correlated with coronary heart disease (CHD) risk, but causality remains uncertain. When folate levels are low, the TT genotype of the common C677T polymorphism (rs1801133) of the methylene tetrahydrofolate reductase gene (MTHFR) appreciably increases homocysteine levels, so "Mendelian randomization" studies using this variant as an instrumental variable could help test causality.<h4>Methods and findings</h4>Nineteen ...[more]

PMID: 22363213

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Project description:Background:Publication bias is a form of scientific misconduct. It threatens the validity of research results and the credibility of science. Although several tests on publication bias exist, no in-depth evaluations are available that examine which test performs best for different research settings. Methods:Four tests on publication bias, Egger's test (FAT), p-uniform, the test of excess significance (TES), as well as the caliper test, were evaluated in a Monte Carlo simulation. Two different types of publication bias and its degree (0%, 50%, 100%) were simulated. The type of publication bias was defined either as file-drawer, meaning the repeated analysis of new datasets, or p-hacking, meaning the inclusion of covariates in order to obtain a significant result. In addition, the underlying effect (β = 0, 0.5, 1, 1.5), effect heterogeneity, the number of observations in the simulated primary studies (N = 100, 500), and the number of observations for the publication bias tests (K = 100, 1,000) were varied. Results:All tests evaluated were able to identify publication bias both in the file-drawer and p-hacking condition. The false positive rates were, with the exception of the 15%- and 20%-caliper test, unbiased. The FAT had the largest statistical power in the file-drawer conditions, whereas under p-hacking the TES was, except under effect heterogeneity, slightly better. The CTs were, however, inferior to the other tests under effect homogeneity and had a decent statistical power only in conditions with 1,000 primary studies. Discussion:The FAT is recommended as a test for publication bias in standard meta-analyses with no or only small effect heterogeneity. If two-sided publication bias is suspected as well as under p-hacking the TES is the first alternative to the FAT. The 5%-caliper test is recommended under conditions of effect heterogeneity and a large number of primary studies, which may be found if publication bias is examined in a discipline-wide setting when primary studies cover different research problems.

Dataset Information

Homocysteine and coronary heart disease: meta-analysis of MTHFR case-control studies, avoiding publication bias.

Publications

Homocysteine and coronary heart disease: meta-analysis of MTHFR case-control studies, avoiding publication bias.

Similar Datasets

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