RAB3A encodes a small GTPase that plays a central role in regulated exocytosis and synaptic vesicle trafficking. As a key regulator of intracellular membrane trafficking, RAB3A cycles between inactive GDP-bound and active GTP-bound forms to control vesicle formation, movement, and fusion 1. The protein regulates calcium-dependent lysosome exocytosis and plasma membrane repair through interactions with effectors SYTL4 and myosin-9 2. In neuronal function, RAB3A is essential for anterograde axonal transport of synaptic vesicle precursors, forming complexes with motor adaptor MADD and kinesin motors KIF1A/1Bβ 3. During sperm exocytosis, GTP-bound RAB3A promotes secretion through its C-terminal domain, while GTP hydrolysis is mandatory for fusion pore opening 4. Disease relevance includes cerebellar ataxia caused by heterozygous RAB3A variants, particularly the recurrent p.Arg83Trp variant, which impairs GTPase activity and effector binding 1. Additionally, hyperphosphorylation of RAB3A by pathogenic LRRK2 in Parkinson's disease disrupts synaptic vesicle transport and synaptic protein distribution 3. RAB3A variants are also associated with amyotrophic lateral sclerosis, affecting motor-mediated transport 5.