RAB18 is a conserved small GTPase that functions as a key regulator of intracellular membrane trafficking by cycling between inactive GDP-bound and active GTP-bound states to recruit downstream effectors 1. RAB18 localizes to multiple organelles, particularly the endoplasmic reticulum (ER) and lipid droplets 2. Primary functions include: (1) mediating ER-lipid droplet contact sites through ZFYVE1 localization, essential for lipid droplet biogenesis and maturation 13; (2) maintaining ER structure 4; and (3) regulating cholesterol biosynthesis through interactions with sterol-modifying proteins EBP and ORP2 5. RAB18 plays critical roles in eye and brain development 6. Loss-of-function RAB18 mutations cause Warburg Micro syndrome, an autosomal recessive disorder characterized by developmental abnormalities 25. Conversely, RAB18 overexpression promotes gastric cancer proliferation and chemoresistance through mitochondrial regulation 7, and exacerbates non-alcoholic fatty liver disease by regulating lipid droplet proteins PLIN2 and PPARγ 8. RAB18 also functions in lipophagy inhibition and copper-induced cell death pathways 9. These opposing roles in development versus disease highlight RAB18's context-dependent importance in metabolic homeostasis and cellular stress responses.