Relative to ADD, the Ng concentrations were significantly lower in the PD (p < 0.0001), PD MCI (p = 0.005), PDD (p < 0.0001), DLB (p = 0.002), CBS (p = 0.03), and PSP (p = 0.004) (Fig. 2a). Here, NRGN is linked to Parkinson disease.