Sorting nexin-21 is a protein that in humans is encoded by the SNX21 gene. This gene encodes a member of the sorting nexin family. Members of this family contain a phox (PX) domain, which is a phosphoinositide binding domain, and are involved in intracellular trafficking. This protein does not contain a coiled coil region, like some family members. The specific function of this protein has not been determined. Multiple transcript variants encoding distinct isoforms have been identified for this gene.