Proteomic screens of mouse embryonic fibroblasts from a knock-in mouse expressing the hyperactive mutant of LRRK2, LRRK2-G2019S, the most common cause of familial PD (28), or LRRK2-G2019S knock-in cell lines, such as HEK293, have identified Rab12 as a substrate of LRRK2, suggesting its involvement in PD (25, 27). The gene discussed is LRRK2; the disease is Parkinson disease.