Figure 2.

Summary schematic of Mendelian randomisation (MR). Single-nucleotide polymorphisms (SNPs) are selected as an instrumental variable to look at the causal relationship between an exposure and an outcome indicated by the red arrow. The method of MR relies on three assumptions indicated by the blue text. Assumption 1: There must be a robust association between the chosen SNPs and exposure variable. Assumption 2: The chosen SNPs must be independent of any confounding factors. Assumption 3: There must be no independent association between the SNPs and outcome variable. Any violation of these assumptions invalidates the study and can limit the method of MR (data from Gala & Tomlinson 2020).