In relation to PSAP and Saposin C protein levels, both experienced a significant decrease of approximately 40% in PD patients compared to controls (PSAP: controls = 1.139 ± 0.2170; PD = 0.6878 ± 0.05014, p < 0.05; Saposin C: controls = 0.2255 ± 0.04037; PD = 0.1203 ± 0.01337, p < 0.05). The gene discussed is PSAP; the disease is Parkinson disease.