The function of IGSF9B (immunoglobulin superfamily member 9B, Ensembl gene identifier ENSG00000080854) is as follows. Transmembrane protein which is abundantly expressed in interneurons, where it may regulate inhibitory synapse development (By similarity). May mediate homophilic cell adhesion (By similarity). Is involved in the organization and maintenance of axon initial segment (AIS) architecture, likely cooperating with PRICKLE2 to regulate ANK3/ANKG localization to AIS (By similarity). .