neuronal phosphoprotein which associates with the cytoplasmic surface of synaptic vesicles and binds to the cytoskeleton. May function in the regulation of neurotransmitter release and of axonogenesis and synaptogenesis. Mutations may be associated with X-linked disorders with primary neuronal degeneration such as Rett syndrome. Two differentially spiced isoforms have been reported. Note: This description may include information from UniProtKB.