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LRRK2 has been on drug developers’ radars for almost 20 years, ever since genetic studies showed that it is one of the most commonly mutated proteins in Parkinson disease (PD). Now, two firms are at last testing the hypothesis that LRRK2 inhibition in patients could slow or halt this devastating neurodegenerative disease. In October, Biogen and partner Denali Therapeutics began a phase III trial of their oral, small-molecule LRRK2 kinase inhibitor BIIB122 (formerly DNL151) in patients with LRRK2-mutated PD.