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

Inclusion Criteria: * 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 Exclusion Criteria: * 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