GPNMB and Parkinson disease: This analysis identified eight proteins (HLA-DQA2, GRN, GPNMB, CD68, C1QTNF1, ENTPD1, SDCBP2, and TLR3) with differentially abundant protein levels in PD cases compared to controls, and two (ITBG2 and TMEM106A) with suggestive association (Supplementary Table 4).