Interaction-based Mendelian randomization with measured and unmeasured gene-by-covariate interactions
Spiller, W.; Hartwig, F. P.; Sanderson, E.; Davey Smith, G.; Bowden, J.
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Studies leveraging gene-environment (GxE) interactions within Mendelian randomization (MR) analyses have prompted the emergence of two methodologies: MR-GxE and MR-GENIUS. Such methods are attractive in allowing for pleiotropic bias to be corrected when using individual instruments. Specifically, MR-GxE requires an interaction to be explicitly identified, while MR-GENIUS does not. We critically examine the assumptions of MR-GxE and MR-GENIUS, and propose sensitivity analyses to evaluate their performance. Finally, we explore the association between body mass index (BMI) and systolic blood pressure (SBP) using data from the UK Biobank. We find both approaches share similar assumptions, though differences between the approaches lend themselves to differing research settings. Where interactions are identified, MR-GxE relies on weaker assumptions and allows for further sensitivity analyses. MR-GENIUS circumvents the need to identify interactions, but relies on the MR-GxE assumptions holding globally. Through applied analyses we find evidence of a positive effect of BMI upon SBP.
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