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

The purpose of this study is to evaluate the efficacy, safety, and pharmacokinetics (PK) of RO7568282 compared with placebo in participants with early-stage Parkinson's disease (PD) on stable symptomatic monotherapy with levodopa.

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