EDN2 and Parkinson disease: Extra simple effect analysis between subgroups across PD and ET revealed a significant difference in group pairs: PD1-ET1 under P1 [t(248) = −3.234, P < 0.05], PD1-ET1 under P2 [t(248) = 10.762, P < 0.05] and PD2-ET2 under P2 [t(248) = 9.451, P < 0.05] (Figure 2).