SLC6A3 and Parkinson disease: In this study, hub genes in the PPI networks were identified for the substantia nigra (SLC6A3, SLC18A2, and TH), putamen (BMP4 and SNAP25), prefrontal cortex area (SNAP25), and cingulate gyrus (CTGF, CDH1, and COL5A1) of PD through the cytoHubba plug-in.