BIIB122-Matching Placebo

A Study to Learn About the Safety of BIIB122 Tablets and Whether They Can Slow the Worsening of Early-Stage Parkinson's Disease in Adults Between the Ages of 30 and 80

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

A Study to Assess if BIIB122 Tablets Are Safe and Can Slow Worsening of Early-Stage Parkinson's Disease in Participants With Specific LRRK2 Genetic Variants Between the Ages of 30 and 80 Using the Movement Disorder Society-Unified Parkinson's Disease Rating Scale