NRGN and Parkinson disease: Despite some studies suggesting alterations in serum and CSF levels of synaptic dopamine potentiators [β-synuclein and growth associated protein 43 (GAP43)]254–260 and markers of synaptic plasticity [neurogranin (Ng), contactin-1 (CNTN-1) and the zinc transporter ZnT3] in PD, inconsistencies between studies and poor correlation with motor severity and cognitive progression make future utility unlikely.259,261–268