The melanocyte-specific transporter protein (OCA2, aka P protein, pink-eyed dilution protein homolog) is postulated to play a role in the processing and intracellular trafficking of tyrosinase (TYR) in the melanosome (Potterf et al. 1998, Toyofuku et al. 2002). It is a 110-kDa integral melanosomal protein with 12 predicted transmembrane domains, suggesting a transport function but its exact physiological role is still unknown. In humans, mutations in the OCA2 gene result in oculocutaneous albinism type 2, a disorder of pigmentation characterised by reduced biosynthesis of melanin in the skin, hair and eyes. This disorder is analogous to the pink-eyed dilution phenotype seen in mice with defective Oca2 (Toyofuku et al. 2002). A single SNP in the OCA2 gene is the major determinant of brown and/or blue eye colour (Sturm 2009).