The forward MR analysis results indicate that elevated cathepsin H levels increase the risk of AD (p = 0.005, odds ratio [OR] = 1.040, 95% confidence interval [CI] = 1.011–1.069), elevated cathepsin B levels decrease the risk of PD (p < 0.001, OR = 0.890, 95% CI = 0.831–0.954), and no significant association was found between cathepsin levels and ALS. The gene discussed is CTSB; the disease is Alzheimer disease.