GDNF and Parkinson disease: Adenoviral GDNF transfer promoted laryngeal function recovery after recurrent laryngeal nerve injury (Araki et al., 2006) and stereotactic gene delivery for neurotrophic factors was well tolerated in individuals with advanced Alzheimer's (nerve growth factor; Rafii et al., 2014) and Parkinson's disease (neurturin; Marks et al., 2016).