Oculocutaneous albinism (OCA) describes a group of inherited disorders of melanin biosynthesis characterized by a generalized reduction in pigmentation of hair, skin and eyes and variable ocular findings including nystagmus, reduced visual acuity and photophobia. Variants include OCA1A (the most severe form), OCA1B, OCA1-minimal pigment (OCA1-MP), OCA1-temperature sensitive (OCA1-TS), OCA2, OCA3, OCA4, OCA5, OCA6 and OCA7 (see these terms).
OCA has an estimated prevalence of 1/17,000 worldwide.
The manifestations of OCA are highly variable depending on the specific subtype. Pigmentation present in the skin, hair and eyes can range from little or none to normal levels and findings of nystagmus, photophobia and reduced visual acuity can be present or absent.
OCA is caused by mutations in several genes that control the synthesis of melanin within the melanocytes. OCA1A, OCA1B, OCA-MP and OCA-TS are caused by mutations in the TYR gene (11q14.3), leading to a total or partial loss of the catalytic activity of tyrosinase. In OCA2, mutations are seen in the OCA2 gene which encodes the OCA2 protein, thought to possibly regulate melanosomal pH and play a role in the trafficking process of melanosomal proteins. OCA3 is due to mutations in the tyrosinase-related protein 1 TYRP1 gene. Studies of mouse melanocytes have shown that Tyrp1 functions to stabilize tyrosinase protein, and that mutations in the TYRP1 gene may cause a delayed maturation and an early degradation of tyrosinase. OCA4 is caused by mutations in the SLC45A2 gene, encoding the membrane-associated transporter protein (MATP) that is responsible for melanosome function and protein transport. OCA 5 is caused by a mutation on chromosome 4q24, whose gene has not yet been discovered. OCA6 is due to mutations in the SLC24A5 gene (15q21.1). Recently discovered OCA7 is due to a mutation in C10orf11 gene (10q22.3).
All forms of OCA are inherited autosomal recessively so genetic counseling is possible.
Last update: April 2013
- Dr Masahiro HAYASHI
- Dr Tamio SUZUKI