Study to Test Effects and Safety of RO7568282 in Early Parkinson's Disease

• Must be aged 40 to 85 years inclusive
• Diagnosis of idiopathic PD
• Has received stable doses of monotherapy treatment with levodopa for at least 2 months prior to baseline
• Movement Disorder Society - Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part IV score of 0 at screening and prior to randomization at baseline
• Hoehn and Yahr (H&Y) Stage ≤ 3 (assessed in off medication state) at screening and prior to randomization at baseline
• Able to swallow whole capsules

• Medical history indicating a parkinsonian syndrome other than idiopathic PD
• Diagnosis of PD dementia
• Diagnosis of a significant neurologic disease other than PD
• Within the last year, unstable or clinically significant cardiovascular disease
• Chronic uncontrolled hypertension
• History or presence of brain magnetic resonance imaging (MRI) scan showing evidence of structural abnormalities, other than related to PD

Note: Other protocol-defined inclusion/exclusion criteria also apply