Glial cell-line derived neurotrophic factor (GDNF), a secreted growth factor of the GDNF family ligands (GFLs) [1], is an important biomedical research target, especially since it has been shown to promote the survival of the midbrain dopaminergic neurons that degenerate in Parkinson’s disease [2]. The gene discussed is GDNF; the disease is Parkinson disease.