A novel and promising approach to the treatment of Parkinson's disease is gene therapy, including viral vector-mediated transfer of candidate genes to enhance dopamine production or the survival of dopaminergic neurons. CERE-120 (AAV-hNGF-hNTN) is a novel gene therapy product that delivers a modified human neurturin (NRTN or NTN) gene (i.e., prepro sequence of human neurturin replaced with the prepro domain of human nerve growth factor b [NGFb]) via an adeno-associated virus type 2 (AAV2)