GDNF and amyotrophic lateral sclerosis: GDNF is a diffusible peptide, involved in neuronal differentiation and survival, and has been identified as potential biomarker in AD in an unbiased proteomic assay (Ray et al., 2007), in amyotrophic lateral sclerosis (Stanga et al., 2018) and is the most potent dopaminergic factor described for the treatment of PD (Garbayo et al., 2016).