A genetic instrument for Mendelian randomization of fibrinogen.
Eur J Epidemiol
Mendelian randomization studies on fibrinogen commonly use a single genetic variant as an instrument, but this may explain only a small proportion of the total phenotypic variance. We examined the contribution of multiple common single nucleotide polymorphisms (SNPs) and haplotypes in the entire fibrinogen gene cluster to plasma fibrinogen levels in two prospective cohorts, for use as instruments in future Mendelian randomization studies. Genotypes for 20 SNPs were determined in 2,778 middle-age (49-64 years) men from the Second-Northwick-Park-Heart Study (NPHS-II). These were replicated in 3,705 men from the Whitehall-II study (WH-II). Plasma fibrinogen levels were determined six times in NPHS-II and three times in WH-II. The minor alleles of four SNPs from the FGB gene, two from the FGA gene, and one from the FGG gene were associated with higher plasma fibrinogen levels. SNP rs1800790 (-455G>A) commonly used in Mendelian randomization studies was associated with R2=1.22% of the covariate adjusted residual variance in fibrinogen level. A variable selection procedure identified one additional SNP: rs2070011 (FGA) altogether explaining R2=1.45% of the residual variance in fibrinogen level. Using these SNPs no evidence for causality between the fibrinogen levels and coronary heart diseases was found in instrumental variables analysis. In the replication cohort, WH-II, the effects of the two SNPs on fibrinogen levels were consistent with the NPHS-II results. There is statistical evidence for several functional sites in the fibrinogen gene cluster that determine an individual's plasma fibrinogen levels. Thus, a combination of several SNPs will provide a stronger instrument for fibrinogen Mendelian randomization studies.
|Title:||A genetic instrument for Mendelian randomization of fibrinogen.|
|Keywords:||Alleles, Coronary Disease, Female, Fibrinogen, Follow-Up Studies, Gene Frequency, Genetic Predisposition to Disease, Great Britain, Humans, Male, Mendelian Randomization Analysis, Middle Aged, Multigene Family, Polymorphism, Single Nucleotide, Prospective Studies, Survival Analysis|
|UCL classification:||UCL > School of Life and Medical Sciences
UCL > School of Life and Medical Sciences > Faculty of Population Health Sciences
UCL > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Cardiovascular Science
UCL > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Epidemiology and Health Care > Epidemiology and Public Health
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