Title: Factorial Mendelian randomization: using genetic variants to assess interactions.

Biography: Factorial Mendelian randomization is the use of genetic variants to answer questions about interactions. Although the approach has been used in applied investigations, little methodological advice is available on how to design or perform a factorial Mendelian randomization analysis. Previous analyses have employed a 2x2 approach, using dichotomized genetic scores to divide the population into 4 subgroups as in a factorial randomized trial.

In the talk, two distinct contexts for factorial Mendelian randomization will be described: for investigating interactions between risk factors, and for investigating interactions between pharmacological interventions on risk factors. I will propose two-stage least squares methods for performing factorial Mendelian randomization, and compare the performance of the method for different choices of instruments. Methods will be illustrated using data from UK Biobank to investigate the interaction between body mass index and alcohol consumption on systolic blood pressure.