Neurotrophic factors, such as brain‐derived neurotrophic factor (BDNF), glial cell‐derived neurotrophic factor (GDNF), nerve growth factor (NGF), transforming growth factor β (TGFβ), insulin‐like growth factor 1 (IGF1), epidermal growth factor (EGF) and fibroblast growth factor 1 (FGF1), are involved in neuronal survival, maintenance and regeneration, and glial activation, malfunctions of which contribute to the pathogenesis of PD.34, 35, 36, 37, 38, 39, 40. Here, GDNF is linked to Parkinson disease.