Biogen and Denali Therapeutics discontinued development of their LRRK2 inhibitor program for idiopathic Parkinson’s after a Phase 2b trial missed its primary endpoint. The randomized study enrolled 648 adults with Parkinson’s and compared the LRRK2-targeted pill BIIB122 (biomarker-guided approach for LRRK2-driven biology) against placebo to test whether degeneration could be slowed. The decision highlights how genetic validation does not always translate into broad clinical efficacy when studied across heterogeneous, real-world patient populations. The companies said they would end development in the idiopathic form, narrowing the path forward for the asset. For investors and researchers tracking target confidence in neurodegeneration, the Phase 2b outcome adds pressure on LRRK2 programs and increases scrutiny on trial design choices for mechanism-based Parkinson’s therapies.