The strongest support for a role of FGF20 in adult mDA neuron survival, however, stems from the meanwhile numerous and reconfirmed associations of polymorphisms in the human FGF20 gene with an increased risk for PD [(Itoh and Ohta, 2013) and references therein; (Nalls et al., 2019)]. This evidence concerns the gene FGF20 and Parkinson disease.