PCSH15 encodes a variety of isoforms with 3 to 11 ectodomains, a transmembrane domain, and a C-terminal cytoplasmic domain (CD). The amino acid sequences of CD1, CD2, and CD3 are entirely different. PCDH15-CD1 showed a limited pattern of expression and was detected in human testis, retina, and cochlea. PCDH15-CD2 expression was present in the human heart, kidney, thymus, spleen, testis, retina and cochlea. PCDH15-CD3 was widely transcribed and detected in almost all of 18 tissues tested. PCDH15 expression in the inner and outer synaptic layers and the nerve fiber layer in human adult and fetal retinas. Additional reactivity in the region of the outer limiting membrane/photoreceptor cell inner segments was observed in adult but not fetal retina.