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

The overall study will consist of three parts (Part 1a, Part 1b and Part 2). Part 1 of this study will evaluate the safety, tolerability and plasma PK of multiple ascending doses (MAD) of KM-819 in healthy older adults (Part 1a) and participants with Parkinson's disease (Part 1b). * Part 1a is a randomized, double-blind, Multiple Ascending Dose (MAD) study in healthy older adults that will include 3 cohorts. * Part 1b is a randomized, double-blind, MAD study in participants with Parkinson's disease that will include 3 cohorts. Part 2 of the study is a randomized, double-blind, multiple dose study in participants with Parkinson's disease that will include 2 cohorts. It is designed to test the safety, tolerability, plasma PK and pharmacodynamic effects of KM-819 in participants with Parkinson's disease. The study will also assess the degree to which those treated with KM-819 will experience gains in overall daily function within the context of improved Parkinson's disease motor and non-motor symptoms in comparison to placebo. Participants will be randomized to receive KM-819 or matching placebo at doses to be determined based on the findings from Part 1 in a 2:1 ratio.