3.1 Selected SNPs for T2DM
After ruling out SNPs did not meet the standard of genome-wide significance (p<5×10-8) and clumping for those in linkage disequilibrium (r2<0.001), 143 SNPs were finally selected for T2DM in our study. Besides, F-statistic of these SNPs were larger than 10 indicating our results were less likely to be biased by weak instruments (29).
3.2 Total effect of T2DM on CVD
We found strong evidence supporting causality of T2DM on subtypes of CVD. Figure 1 shows the total effect of T2DM on CHD, MI and stroke. One-unit higher log odds of T2DM increased 16% risk of CHD (OR: 1.16, 95%CI 1.12-1.21, p<0.001), 15% risk of MI (OR: 1.15, 95%CI 1.10-1.20, p<0.001) and 10% risk of stroke (OR: 1.10, 95%CI 1.06-1.13, p<0.001). Details of genetic associations of T2DM on CVD were shown in Supplementary Table 15-17.
3.3 Effect of T2DM on cardiometabolic factors
Figure 2 shows that one-unit higher log odds of T2DM was associated with increased standard deviation (SD) of SBP (β=0.77, 95% CI: 0.49 to 1.04, p<0.001), DBP (β=0.22, 95%CI: 0.06 to 0.38, p=0.009), TG (β=0.08, 95% CI: 0.02 to 0.14, p=0.002), and WHR (β=0.05, 95% CI: 0.03 to 0.07, p<0.001), and was also associated with decreased SD of LDL (β= -0.07, 95% CI: -0.12 to -0.01, p=0.008), HDL (β= -0.15, 95% CI: -0.21 to -0.09, p<0.001), TC (β= -0.06, 95% CI: -0.12 to -0.00, p=0.025) and insulin sensitivity (β= -0.31, 95% CI: -0.55 to -0.07, p=0.012). We failed to find causal effect of T2DM on BMI (p=0.615), VLDL (p=0.168), hyperthyroidism (p=0.213) and hypothyroidism (p=0.159). Genetic associations of T2DM on each cardiometabolic factor were shown in Supplementary Table 18-29 and those MR results above were shown in details in Supplementary Table 30.
3.4 Effects of cardiometabolic factors on CVD
Figure 3 shows the estimate of causal effect of one SD increase in each cardiometabolic factor on each subtype of CVD after adjusting for T2DM. Estimate of log odds of CHD for one SD increase in SBP, DBP, TG, HDL, WHR and insulin sensitivity was 1.03 (95%CI: 1.02-1.04, p<0.001), 1.05 (95%CI: 1.04-1.06, p<0.001), 1.22 (95%CI: 1.13-1.32, p<0.001), 0.89 (95%CI: 0.65-1.21, p=0.521), 1.06 (95%CI: 0.87-1.30, p=0.568), and 1.00 (95%CI: 0.98-1.01, p=0.817), respectively. The estimated OR of MI for genetically determined one SD increase in SBP, DBP, TG, HDL, WHR and insulin sensitivity was 1.03 (95%CI: 1.02-1.03, p<0.001), 1.05 (95%CI: 1.04-1.06, p<0.001), 1.22 (95%CI: 1.12-1.33, p<0.001), 0.91 (95%CI: 0.70-1.19, p=0.569), 1.03 (95%CI: 0.83-1.27, p=0.812) and 0.99 (95%CI: 0.97-1.02, p=0.503), respectively. Likewise, one SD increase in genetically determined SBP, DBP, TG, WHR and insulin sensitivity was associated with 3% (OR: 1.03, 95% CI: 1.03-1.04, p<0.001), 4% (OR: 1.04, 95% CI: 1.04-1.05, p<0.001), 0.4% (OR: 1.00, 95% CI: 0.95-1.06, p=0.869), 22% (OR: 0.22, 95% CI: 1.19-1.24, p=0.038), 4% (OR: 1.04, 95%CI: 0.88-1.22, p=0.675) higher risk of stroke and 1% (OR: 0.99, 95%CI: 0.98-1.00, p=0.102) lower risk of stroke, respectively. Regression-based MVMR failed to be performed to estimate the effect of TC and LDL on subtypes of CVD, HDL on stroke for the sake of inadequate SNPs after adjusting for T2DM. Genetic associations of each cardiometabolic factor on each subtype of CVD after adjusting for T2DM were shown in Supplementary Table 31-47.
3.5 Mediation effects of cardiometabolic factors on CVD
After excluding cardiometabolic factors that were not causally influenced by T2DM and those did not have causal effect on CVD subtypes, we took SBP, DBP and TG for mediation analysis. Figure 4 shows the proportion of the effect of T2DM on subtypes of CVD mediated by each cardiometabolic factor included in mediation analysis. For causal effect of T2DM on CHD, the percentage mediated by SBP, DBP and TG was 16% (8%-24%), 7% (1%-13%), and 10% (2%-18%), respectively. The mediation effect of SBP, DBP and TG on MI was estimated to account for 14% (7%-22%), 7% (1%-13%), and 11% (2%-20%), respectively. The proportion of the effect of T2DM on stroke mediated by SBP, DBP and TG was 26% (13%-39%), 10% (2%-19%) and 0.4% (-4%-5%), respectively. Thus, we identified SBP, DBP and TG were main mediators on CHD and MI, SBP and DBP also had significant mediation effect on stroke. Total mediation effect of combination of SBP, DBP and TG on CHD, MI and stroke was 29%, 26% and 13% respectively. Details were shown in Supplementary Table 48-50.
3.6 Sensitivity analyses
Part of results of sensitivity analyses for T2DM on CVD subtypes and three mediators (SBP, DBP and TG) were shown in Table 1. Egger regression results of T2DM-CHD, T2DM-MI, T2DM-DBP and T2DM-TG indicated there might be horizontal pleiotropy existing (p>0.05 with non-zero Egger intercept), however, results from MR-PRESSO outlier-corrected were more consistent with IVW main analysis which are shown in Supplementary Table 51-56. Results of Simple median and Weighted median were mostly statistically significant (p<0.05) which indicated that our results were less likely influenced by weak instrument bias. Other sensitivity analyses including single SNP analysis, leave-one-out analysis both provided consistent results with our main analysis and were shown in Supplementary Table 57-62.