In the ISR gene set, classifying healthy vs. prodromal PD, the genes KDM6B, CEBPB, CDC42, S100P, HLA-DRB1, LITAF, CARS2, ATF2, IRF7, PSEN1, ERVW-1, ATF4, NFE2L2, SLC38A2, CREBBP, LARS1, CXCL8, IARS1, and ATF6 consistently ranked in the top 20 in all three time points. Here, S100P is linked to Parkinson disease.