Cell surface proteoglycan that bears heparan sulfate. Regulates dendritic arbor morphogenesis (By similarity). Interacts (via cytoplasmic domain) with SARM1 (By similarity). Forms a complex with SDCBP and PDCD6IP (PubMed:22660413). O-glycosylated with core 1 or possibly core 8 glycans. Contains heparan sulfate. Belongs to the syndecan proteoglycan family. Extended N-terminus.