NEFL and Parkinson disease: Figure 1a and b demonstrates that the GFAP and NfL levels were significantly higher in the PD group than in the HC group (PD group: 144 ± 65.6 pg/mL, HC group: 115 ± 39.1 pg/mL, p = 0.0363; and PD group: 39.8 ± 32.5 pg/mL, HC group: 13.9 ± 4.45 pg/mL, p < 0.0001; respectively).