Plasma levels of NFL in PD and HCs were similar by using either K2- (PD: 8.89 ± 2.38 pg/ml, HC: 8.95 ± 3.42 pg/ml, P = 0.961, Figure 2C) or K3-EDTA collection (PD: 9.53 ± 2.26 pg/ml, HC: 8.81 ± 3.03 pg/ml, P = 0.61, Figure 2D). This evidence concerns the gene NEFL and Parkinson disease.