LRRK2 and Parkinson disease: In this issue of Science Advances, Bogacki et al. (5) characterize GPNMB in macrophages and highlight its role as a lysosomal protein that is delivered to the cell surface under conditions of lysosome stress; their work connects GPNMB with another important, PD-linked gene product, leucine-rich repeat kinase 2 (LRRK2) (6).