NRTN and Parkinson disease: AAV2-neurturin demonstrated consistently promising efficacy across rodent and NHP models—failure to replicate this in human patients has been ascribed to challenges of product delivery,[28] relatively greater nigrostriatal and axonal compromise in human PD patients compared to MPTP and 6-OHDA induced animal models, [21,22] and failure to address the degenerative drive in PD induced by alpha-synucleopathy.