Higher genetically instrumented plasma SAP concentrations were associated with AD (odds ratio 1.07, 95% confidence interval (CI) 1.02; 1.11, p = 1.8 × 10−3), Lewy body dementia (odds ratio 1.37, 95%CI 1.19; 1.59, p = 1.5 × 10−5) and plasma tau concentration (0.06 log2(ng l−1) 95%CI 0.03; 0.08, p = 4.55 × 10−6). This evidence concerns the gene APCS and Alzheimer disease.