In healthy adult human brains, GDNF mRNA levels are typically low; however, they have been found to increase under pathological conditions such as Parkinson’s disease, not only in neurons but also in astrocytes, microglia, and macrophages (Nakagawa et al., 2005; Bäckman et al., 2006; Azevedo et al., 2020). The gene discussed is GDNF; the disease is Parkinson disease.