Types and Phenotypes of Oculocutaneous Albinism (OCA)
Type (OMIM Number) | Defect or Mutation | Phenotypes | Comments |
|---|---|---|---|
Type I | Mutations in TYR gene result in absent (OCA1A) or reduced (OCA1B) tyrosinase activity. Tyrosinase catalyzes several steps in melanin synthesis. | In OCA1A, skin and hair are milky white, and eyes are blue-gray (decrease in visual acuity is the most severe in this form of OCA). In OCA1B, pigmentary dilution ranges from obvious to subtle. | OCA1A comprises 40% of all OCA. |
Type II (203200) | P (pink-eyed) gene The function of the P protein is not yet known but may involve regulation of organelle pH and accumulation of vacuolar glutathione. | OCA type II has phenotypes with pigmentary dilution that ranges from minimal to moderate. Pigmented nevi and lentigines may develop if skin is exposed to the sun; some lentigines become large and dark. Eye color varies greatly. | Tyrosinase activity is present. Type II comprises 50% of all OCA and is the most common form of OCA in Africa. |
Type III (203290) | Tyrosinase-related protein 1 (TYRP1) gene The product of this gene is important in the synthesis of eumelanin, the most common of the 3 types of melanin that give skin, hair, and eyes their color. | In OCA type III, skin is brown, hair is rufous (reddish), and eye color can be blue or brown. | Type III occurs only in people with otherwise dark skin (Fitzpatrick skin types III to V—see table Fitzpatrick Skin Type Classification). |
Type IV (606574) | SLC45A2 gene This gene codes a membrane transporter protein involved in tyrosinase processing and trafficking of proteins to melanosomes. | In OCA type IV, the phenotype is similar to that for type II. | Type IV is an extremely rare form. It is the most common form of OCA in Japan. |
Type V (615312) | Linked to chromosome 4q24 This chromosome is located in a region that may code for lysosomal proteins. | In OCA type V, skin is white, and hair is golden-colored. | — |
Type VI (113750) | Linked to mutations in gene SLC45A5 This gene encodes a membrane transporter protein. | In OCA type VI, skin can be white, and hair can be light at birth and may darken with age. | — |
Type VII (615179) | Mutations in gene C10ORF11 This gene encodes a leucine-rich protein that may play a role in melanocyte differentiation. | In OCA type VII, skin pigment is decreased, and hair can range from white to brown. | — |
Type VIII (619165) | Linked to a mutation in gene dopachrome tautomerase (DCT) on chromosome 13q32 This gene encodes an enzyme that plays a role in modification of skin pigment color. | In OCA type VIII, skin and hair are mildly hypopigmented. | — |