BDNF and Parkinson disease: Preclinical studies with 6-hydroxydopamine (6-OHDA)-induced early parkinsonism have shown that the targeted delivery of genes coding for neurotrophic factors such as human (hGDNF) [22], rat brain-derived neurotrophic factor (rBDNF) [2], or hCDNF [6] can rescue dopaminergic neurons from neurodegeneration.