Several pivotal clinical trials have evaluated dose escalation, safety, and efficacy of gene therapy in PD patients including safety study of AADC gene therapy, genetic convection-enhanced delivery/AAV2-GDNF (Björklund et al., 2000; Bäckman et al., 2006; McFarthing et al., 2019), AAV2-NTN (Marks et al., 2008), AAV-hAADC-2 (Christine et al., 2019; McFarthing et al., 2019; Christine et al., 2022), and rAAV-GAD (McFarthing et al., 2019); but none are currently accessible to PD patients. Here, GDNF is linked to Parkinson disease.