We found that higher plasma SAP values increased the risk of AD (OR 1.07, 95%CI 1.02; 1.11, p = 1.8 × 10−3) and LBD (OR 1.37, 95%CI 1.19; 1.59, p = 1.5 × 10−5), implying that pharmaceutical depletion of SAP might reduce the risk of both diseases. This evidence concerns the gene APCS and Alzheimer disease.