OCIAD1 (OCIA domain containing 1), also known as OCIA (ovarian carcinoma immunoreactive antigen), TPA018 or ASRIJ, is a 245 amino acid endosomal protein that contains one OCIA domain and belongs to the OCIAD1 family. OCIAD1 exists as two alternatively spliced isoforms (termed OCIAD1 isoform A and B) that localize to different tissues; isoform A localizes to prostate, brain, mammary gland, testis, placenta and ovary, whereas isoform B is restricted to the central nervous system. The gene enocoding OCIAD1 maps to human chromosome 4, which represents approximately 6% of the human genome, contains nearly 900 genes and is associated with Huntington's disease, Ellis-van Creveld syndrome, methylmalonic acidemia and polycystic kidney disease.