Protocadherin 15 is a 250-270kD "other" member of the nonclustered group of the protocadherin family of molecules. In the adult, it is expressed on the base of hair cell stereoclila in the Organ of Corti, on cerebellar granule cells, and on rod and cone photoreceptors. In the ear, it is expressed as a homodimer, and binds (in trans) to cadherin 23 homodimers on adjacent stereocilia. Mature human PCDH-15 is a type I transmembrane protein that is 1929aa in length. It contains a 1350aa extracellular domain aa27-1376 plus a 558aa cytoplasmic region. There are 11 cadherin domains in the ECD aa40-1259. Multiple splice forms are reported. One is a soluble 110kD form that shows a five aa substitution for aa957-1955. Another contains a seven aa substitution for aa1119-1125. Others show substitutions or deletions in either the extracellular or cytoplasmic domains. Over aa27-1376, human PCDH-15 shares 95% aa identity with mouse PCDH-15.