GDNF Gene Therapy for Parkinson's Disease

Key Inclusion Criteria: * Male and female adults 35-75 years of age (inclusive) * Diagnosed with Parkinson's disease * Modified Hoehn and Yahr stage I-III OFF medication * Time since receiving a clinical diagnosis of PD and disease severity consistent with one of the following: 1. EITHER: Less than 5 years since clinical diagnosis of PD and mild to moderate UPDRS III OFF score 2. OR: At least 4 years since clinical diagnosis of PD and moderate to severe UPDRS III OFF score * Responsiveness to levodopa Key Exclusion Criteria: * Atypical parkinsonism * Severe dyskinesia * Presence of dementia, psychosis, substance abuse or qualify as "severe depression" * Prior brain surgery (i.e. deep brain stimulator or DBS implantation) or other brain imaging abnormalities * Receiving an investigational drug * History of cancer or poorly controlled medical conditions that would increase surgical risk * Inability to tolerate laying flat in an MRI or allergy to gadolinium