Safety and Pharmacodynamic Effects of BIIB122 in Participants With LRRK2-Associated Parkinson's Disease (LRRK2-PD)

This study is testing the safety and biological effects of a new drug called BIIB122 in people with Parkinson's disease who carry a mutation in the LRRK2 gene — a known genetic cause of Parkinson's. This drug aims to slow or modify how the disease progresses. **You may be eligible if...** - You are between 30 and 80 years old (or 30 or older if you carry two copies of the LRRK2 mutation) - You have been confirmed to carry a pathogenic (disease-causing) LRRK2 gene mutation through genetic testing - You have been clinically diagnosed with Parkinson's disease meeting standard diagnostic criteria **You may NOT be eligible if...** - You have another significant neurological disorder (such as stroke or dementia) in the past 5 years - You show signs of atypical parkinsonism (e.g., multiple system atrophy or progressive supranuclear palsy) - You have previously had brain surgery for Parkinson's (e.g., deep brain stimulation) - You have previously participated in the BIIB122 LUMA study or any gene therapy trial for Parkinson's - You have physical conditions that would interfere with motor assessments over time (such as severe arthritis or serious injuries) - You have abnormal vital signs or abnormal lung function test results Talk to your doctor to see if this trial is right for you.