A Study to Evaluate Safety and Efficacy of KM-819 in Healthy Adults and Participants with Parkinson's Disease

Inclusion Criteria: * Participant is a healthy volunteer or has a clinical diagnosis of idiopathic Parkinson's disease. * Participant is on a stable dose of medications to treat Parkinson's disease at least 8 weeks prior to randomization * Presence of idiopathic Parkinson's disease Hoehn and Yahr Stage ≤ 4 * History or current use of dopamine/dopaminergic drugs, levodopa with decarboxylase inhibitor or dopaminergic agonists, with a stable dosage for at least 30 days prior to Screening * Body mass index (BMI) within the range 18.5 to 35 kg/m2 (inclusive) * A male participant must not have a pregnant or breastfeeding partner and must agree to use a highly effective contraception method starting from Screening and refrain from donating sperm during this period * A female participant is eligible to participate if she is not pregnant, not breastfeeding Exclusion Criteria: * Diagnosis of neurodegenerative disorder other than idiopathic Parkinson's disease resulting in dementia or atypical parkinsonism * Life-time history of a suicide attempt as determined by the Columbia-Suicide Severity Rating Scale (C-SSRS) for the Screening * Evidence of cognitive decline defined by the Montreal Cognitive Assessment (MoCA) score ≤25 for healthy normal population (Part 1a) and ≤21 for the patient population (Part 1b and Part 2) * History of levodopa-induced motor fluctuations or dyskinesia * Prior surgical treatment for Parkinson's disease * Clinically significant brain abnormalities on or con…