RAB12 is a small GTPase that regulates intracellular membrane trafficking by cycling between inactive GDP-bound and active GTP-bound states, recruiting downstream effectors to mediate vesicle formation, movement, tethering, and fusion. It plays roles in protein transport from recycling endosomes to lysosomes and in autophagy regulation. RAB12 is a direct substrate of the Parkinson's disease-associated kinase LRRK2; phosphorylation at Ser106 by LRRK2 occurs at endolysosomal membranes and enhances recruitment of the RILP effector family to suppress primary ciliogenesis and regulate centrosome homeostasis in astrocytes 1. In mast cells, Rab12 negatively regulates exocytosis through RILP binding 2, and LRRK1-mediated phosphorylation of Rab12 shifts its effector selectivity among RILP family members 3. RAB12 also mediates trans-Golgi network export of wild-type epidermal growth factor receptor (EGFR) in coordination with the AP-1 adaptor complex 4. Pathologically, elevated phospho-Ser106 RAB12 serves as a blood biomarker of LRRK2 G2019S mutation status in Parkinson's disease patients and correlates with motor disease severity 5. In choroideremia, loss of RAB12 prenylation due to CHM mutations impairs autophagy through increased mTORC1 signaling 6. Recent evidence suggests RAB12 negatively regulates osteogenic differentiation in osteoporosis by controlling glucose metabolism through the PCBP1-GLUT1 axis 7. LRRK2 inhibitors such as MLi-2 reduce RAB12 phosphorylation levels, supporting kinase inhibition as a therapeutic approach in LRRK2-associated Parkinson's disease.