CTSL and Alzheimer disease: The result of the two-sample MR analysis revealed that high level of cathepsin L (CTSL) was associated with a lower risk of AD (IVW: Odds Ratio (OR) = 0.962, 95% confidence interval (CI) = 0.936–0.989, p = 0.005) and high level of cathepsin H (CTSH) was associated with a high risk of AD (IVW: OR = 1.039, 95% CI = 1.006–1.073, p = 0.019) (Figure 1A).