This neuroprotective treatment paradigm still needs to be refined, but encouraging preliminary results have been obtained for Parkinson disease with neurturin (NRTN), a structural and functional analogue of GDNF that protects dopaminergic neurones.73, 74 In a double-blind phase II trial, 58 patients with advanced Parkinson disease were randomly assigned, in a 2:1 ratio, to receive either a bilateral injection of AAV2-NRTN into the putamen or sham surgery.75 The primary endpoint was the change from baseline to 12 months in the motor subscore of the unified Parkinson disease rating scale. Here, GDNF is linked to Parkinson disease.