In addition to the classical neurotrophic factors, the newly discovered conserved cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) have also been reported to have trophic effects on nigral DA neurons in normal animals and neuroprotective effects on these neurons in animal PD models (Lindholm et al., 2007; Garea-Rodríguez et al., 2016; Lindahl et al., 2017). Here, CDNF is linked to Parkinson disease.