Biogen and Denali Therapeutics said their investigational Parkinson’s therapy targeting LRRK2 failed in a randomized trial to slow neurodegeneration. The study randomized 648 adults with Parkinson’s to either placebo or the LRRK2-directed pill, dealing a setback to the broader idea that blocking LRRK2 could slow disease across patient populations. The result marks a meaningful reversal for a scientific strategy that has previously been fueled by genetics linking LRRK2 mutations to a hereditary form of Parkinson’s and by earlier mechanistic evidence suggesting potential benefit. The companies will need to reassess whether LRRK2 remains viable as a disease-modifying target or whether selection and trial design require revision.