GDNF and Parkinson disease: This article does not delve into the mDA ontogenic and PD-associated programmed cell death (apoptosis; Burke, 2004; Savitt et al., 2005; Erekat, 2018; Robinson et al., 2018) or the role of “classical” neurotrophic factors, such as glial cell derived neurotrophic factor (GDNF), brain derived neurotrophic factor (BDNF), cerebral dopamine neurotrophic factor and mesencephalic astrocyte derived neurotrophic factor (Chmielarz and Saarma, 2020), in this context.