Although the potential neuroprotective effects of these neurotrophic factors are undisputed, unfortunately in a randomized controlled trial of intraputamenal infusion of recombinant human GDNF in patients with PD, there is no remarkable improvement in patients receiving GDNF (Lang et al., 2006; Ibáñez and Andressoo, 2017). Here, GDNF is linked to Parkinson disease.