exposure and then as the outcome. To test the suitability of the MR Egger method, the I2GX statistic was calculated to quantify the degree of regression dilution bias due to measurement error of SNP-exposure effects (Bowden et al., 2016). We also calculated the mean F statistic as an indicator of instrument strength. Steiger filtering was conducted to confirm the direction of effect (Hemani, Tilling, & Davey Smith, 2017). If a SNP from the instrument was unavailable in the outcome, an attempt to find proxies was made with a minimum LD r2 = 0.8 and palindromic SNPs were aligned with Minor allele frequency < 0.3.
