ACVR1, KLK6, SELENOP, SLC38A2, and so on were among the most upregulated proteins and DDC, TH, TPH2, SLC6A3, FCER1G, ADIRF, and so on were among the most downregulated proteins in PD compared to HC (Figure 3A). This evidence concerns the gene SLC6A3 and Parkinson disease.