RAB3GAP2 is the non-catalytic regulatory subunit of the RAB3GAP complex, which functions as a guanine nucleotide exchange factor (GEF) for RAB18 and a GTPase-activating protein (GAP) for various Rab proteins 1. The complex promotes GDP release from RAB18, converting inactive RAB18-GDP to active RAB18-GTP, and recruits RAB18 to the cis-Golgi membrane and endoplasmic reticulum where it maintains proper ER structure 1. RAB3GAP2 is essential for normal eye and brain development and modulates both basal and rapamycin-induced autophagy through effects on autophagosomal biogenesis 23. In skeletal muscle, RAB3GAP2 functions as a negative regulator of endothelial cell proliferation and angiogenesis, with lower expression associated with increased capillary-to-fiber ratio and elite endurance performance 4. RAB3GAP2 also participates in cholesterol biosynthesis through RAB18-dependent regulation of sterol mobilization 5. Biallelic RAB3GAP2 mutations cause Warburg Micro syndrome and Martsolf syndrome, autosomal recessive disorders characterized by congenital cataracts, intellectual disability, and hypogonadotropic hypogonadism 67. Disease severity correlates with mutation type, with complete loss-of-function mutations causing more severe Warburg Micro syndrome, while partially-preserved function variants cause milder Martsolf syndrome 78.