CD33 and Alzheimer disease: In the blood CD33 mRNA level, 5 IVs were available, and the IVW results indicated that each one standard deviation increase in blood CD33 gene expression was leading to a higher risk of AD (OR [95% CI] = 1.156 [1.080, 1.238], p = 3.25e-05), and such results were supported with another 3 MR methods, including weighted median (OR [95% CI] = 1.162[1.080, 1.250], p = 5.08e-05), simple mode (OR [95% CI] = 1.211[1.071, 1.370], p = 0.038), and weighted mode (OR [95% CI] = 1.165[1.088, 1.249], p = 0.012).