Syntaxin-binding protein 2, also known as UNC18B, is a protein that in humans is encoded by the STXBP2 gene. The STXBP2 gene is mapped to human chromosome 19p13.3-p13.2 and to the proximal arm of mouse chromosome 8. And this gene encodes a member of the STXBP/unc-18/SEC1 family. The encoded protein is involved in intracellular trafficking, control of SNARE (soluble NSF attachment protein receptor) complex assembly, and the release of cytotoxic granules by natural killer cells. Additionally, UNC18B is expressed predominantly as a 2.4-kb message in placenta, lung, liver, kidney, and pancreas, as well as in peripheral blood lymphocytes. Mutations in this gene are associated with familial hemophagocytic lymphohistiocytosis. Alternatively spliced transcript variants encoding different isoforms have been noted for this gene.