A Study to Evaluate the Efficacy and Safety of Intravenous (IV) Prasinezumab in Participants With Early-Stage Parkinson's Disease

Open to people ages 50-85

• Body weight within 40-110 kilograms (kg) (88-242 pounds [lbs]) and a body mass index within the range 18-34 kg/m2
• Diagnosis of idiopathic PD based on Movement Disorder Society (MDS) criteria
• Has received monotherapy treatment
• An MDS-UPDRS Part IV score of 0 at screening and prior to randomization
• Hoehn and Yahr (H&Y) Stage 1 or 2 off medication at screening and prior to randomization
• Agreement to adhere to the contraception requirements

• Pregnant or breastfeeding, or intention of becoming pregnant during the study or within the time frame in which contraception is required
• Medical history indicating a parkinsonian syndrome other than idiopathic PD
• Diagnosis of a significant neurologic disease other than PD
• Chronic uncontrolled hypertension