Microtubule-binding protein which directly binds tubulin and is involved in both polymerization and stabilization of microtubules (By similarity). Through its action on microtubules, may participate in the refinement of axons by negatively regulating axonal and leading processes branching (By similarity). Plays a crucial role in neuron polarization and migration in the cerebral cortex and the hippocampus (By similarity). Regulates voltage-gated sodium channels transport and function (PubMed:15282281, PubMed:33245860). May also play a role in MAPK signaling (By similarity). Required for the development of axonal initial segment-targeting inhibitory GABAergic synapses made by chandelier neurons (By similarity). Interacts with SCN8A; regulates SCN8A activity (PubMed:15282281, PubMed:21566136, PubMed:33245860). Interacts with SCN1A; may regulate SCN1A activity (PubMed:19406745, PubMed:21566136). Interacts with SCN5A; the interaction is direct and may regulate SNC5A density at membranes and function (PubMed:21817159). May also interact with SCN2A and SCN11A (PubMed:19406745, PubMed:21566136). Interacts with MAPK8IP2; may regulate the MAPK8IP2 scaffolding activity (PubMed:11378392). Not secreted. Localizes to the lateral membrane and intercalated disks of myocytes. Ubiquitously expressed. Predominantly expressed in the nervous system. May be phosphorylated. The disease is caused by variants affecting the gene represented in this entry. Belongs to the heparin-binding growth factors family.