Mediates homophilic cell-cell adhesion. Widely expressed (PubMed:9585423, PubMed:29982980). Expressed in the cochlea, in Deiters' cells, possibly at contact sites with the basilar membrane (PubMed:29961571, PubMed:29982980). Expressed in both outer and inner auditory hair cells (PubMed:29961571, PubMed:29982980). In the stria vascularis, detected in the basal cell layer (PubMed:29961571). Not detected in thymocytes, lymphocytes, macrophage or dendritic cells (PubMed:9585423). Mutant mice display early-onset progressive sensorineural hearing impairment that is more pronounced in the high frequencies. They show an altered organization of outer hair cells and supporting cells and degeneration of the organ of Corti, accompanied by mild degeneration of spiral ganglion neurons, that is most pronounced at the cochlear base. Belongs to the myelin P0 protein family.