We performed a 15 - to 24-month , multicenter , double-blind trial in patients with advanced Parkinson disease ( PD ) who were randomly assigned to receive bilateral AAV2-neurturin injected bilaterally into the substantia nigra ( 2.0 10 ( 11 ) vector genomes ) and putamen ( 1.0 10 ( 12 ) vector genomes ) or sham surgery .