Pre-Gene Therapy Study in Parkinson's Disease and Multiple System Atrophy

Inclusion Criteria: * Diagnosis of Idiopathic PD * Diagnosis of MSA-P * One to six years from clinical diagnosis of PD * Less than 4 years from clinical diagnosis of MSA with expected survival \>3 years * Stable medication regimen * Ability to walk with or without an assistive device Exclusion Criteria: * Movement disorder due to known cerebrovascular disease, brain tumor, trauma, exposure to parkinsonian-linked toxicants or other neurological diseases * Presence of dementia, psychosis, substance abuse or poorly controlled depression * Prior brain surgery (i.e. deep brain stimulation) or other brain imaging abnormalities * History of cancer or poorly controlled medical conditions * Receiving an investigational drug NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.