SNAPIN encodes a multifunctional adaptor protein that plays critical roles in vesicle trafficking, autophagy-lysosomal function, and neurodevelopment. As a component of the BLOC-1 and BORC complexes, SNAPIN regulates lysosome-related organelle biogenesis and lysosomal positioning at the cell periphery 1. The protein is essential for maintaining lysosomal acidification and autophagosome maturation in macrophages by preventing proton leak from lysosomes 2. In neurons, SNAPIN undergoes phosphorylation by p38α-MAPK at serine 112, which modulates retrograde axonal transport of BACE1 and influences amyloid pathology in Alzheimer's disease 3. The protein also promotes pancreatic β-cell proliferation by regulating cell cycle progression through modulation of CDK2, CDK4, and CCND1 expression 4. SNAPIN interacts with various cellular partners including PUMILIO2 and NANOS1 in male germ cells, suggesting roles in translational regulation 5, and with G-protein coupled receptor PKR2, affecting receptor trafficking 6. Pathogenic bi-allelic variants in SNAPIN cause severe prenatal-onset neurodevelopmental disorders characterized by brain anomalies, craniofacial defects, and skeletal abnormalities, with zebrafish models demonstrating defective retrograde vesicle transport and autophagy activation 1.