Furthermore, a combination of five peptides, including SPP1, LRP1, Colony-stimulating factor receptor 1 (CSFR1), Ephrin type-A receptor 4 (EPHA4) and Tissue inhibitor of metalloproteinases-1 (TIMP1), can improve the AUC to 0.873 (specificity: 80.0%; and sensitivity: 76.7%) in differentiating PD patients from healthy subjects and can also differentiate PD from AD patients very well with an AUC of 0.990 (specificity: 97.4%; and sensitivity: 95.0%). Here, TIMP1 is linked to Alzheimer disease.