L1CAM and Parkinson disease: In this study, we discovered four immune-related hub genes (SLC18A2, L1CAM, S100A12, and CXCR4) and seven peripheral immune cell types (neutrophils, Tfh cells, MDSCs, Th1 cells, peripheral immature B cells, DCs, and NK cells) that are closely related to the pathogenesis of PD.