GDF15 and COVID-19: Leave-one-out analysis did not detect any substantial violations of the causal effect of GDF-15 on severe COVID-19 in individuals carrying the risk alleles (see Fig. 4), indicating that the results were stable.MR-Egger regression analysis (intercept = −0.015, P = .71) and MR-PRESSO (P = .92) did not support pleiotropy.