Biochemical analyses showed that serum levels of mBDNF and mBDNF/proBDNF in the po-PD group were significantly lower than in the po-NPD group (19.24 ± 7.20 vs. 25.05 ± 7.67 ng/ml for mBDNF, t = 4.392, df = 154, p < 0.0001; 0.09 ± 0.05 vs. 0.16 ± 0.14 for mBDNF/proBDNF, t = 5.179, df = 154, p < 0.0001). The gene discussed is BDNF; the disease is Parkinson disease.