Oculocutaneous albinism (OCA) is a form of albinism involving the eyes (oculo-), the skin (-cutaneous), and according to some definitions, the hair.
Overall, an estimated 1 in 20,000 people worldwide are born with oculocutaneous albinism. OCA is caused by mutations in several genes that control the synthesis of melanin within the melanocytes.
Four types of oculocutaneous albinism have been described, all caused by a disruption of melanin synthesis and all autosomal recessive disorders.:864
| Name || OMIM || Gene || Description|
| OCA1 || 203100 || TYR || OCA1 is caused by an alteration of the tyrosinase gene, and can occur in two variations. The first is OCA1a, and means that the organism cannot develop pigment at all. The hair is usually white (often translucent) and the skin very pale. Vision usually ranges from 20/200 to 20/400. The second is OCA1b, which has several subtypes itself. Some individuals with OCA1b can tan and also develop pigment in the hair. One subtype of OCA1b is called OCA1b TS (temperature sensitive), where the tyrosinase can only function below a certain temperature, which causes the body hair in cooler body regions to develop pigment (i.e. get darker). (An equivalent mutation produces the coat pattern in Siamese cats.) Another variant of OCA1b, called Albinism, yellow mutant type (OMIM: 606952) is more common among the Amish than in other populations, and results in blonde hair and the eventual development of skin pigmentation during infancy, though at birth is difficult to distinguish from other types. About 1 in 40,000 people have some form of OCA1.|
| OCA2 || 203200 || OCA2 || The most common type of albinism, is caused by mutation of the P gene. People with OCA2 generally have more pigment and better vision than those with OCA1, but cannot tan like some with OCA1b. A little pigment can develop in freckles or moles. People with OCA2 usually have fair skin but often not as pale as OCA1, and pale blonde to golden, strawberry blonde, or even brown hair, and most commonly blue eyes. Affected people of African descent usually have a different phenotype (appearance): yellow hair, pale skin, and blue, gray or hazel eyes. About 1 in 15,000 people have OCA2. The gene MC1R doesn't cause OCA2, but does affect its presentation.|
| OCA3 || 203290 || TYRP1 || Has only been partially researched and documented. It is caused by mutation of the tyrosinase-related protein-1 (Tyrp1) gene. Cases have been reported in Africa and New Guinea. Affected individuals typically have red hair, reddish-brown skin and blue or gray eyes. Variants may include rufous oculocutaneous albinism (ROCA or xanthism) (OMIM: 278400). The incidence rate of OCA3 is unknown.|
| OCA4 || 606574 || SLC45A2 || Is very rare outside Japan, where OCA4 accounts for 24% of albinism cases. OCA4 can only be distinguished from OCA2 through genetic testing, and is caused by mutation of the membrane-associated transporter protein (MATP) gene. Several German patients were identified in 2004.|
Oculocutaneous Albinism information
- 1 2 "Oculocutaneous albinism - Genetics Home Reference".
- ↑ http://ghr.nlm.nih.gov/condition/oculocutaneous-albinism
- ↑ http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=EN&Expert=55
- ↑ Grønskov K, Ek J, Brondum-Nielsen K (2007). "Oculocutaneous albinism". Orphanet Journal of Rare Diseases. 2: 43. doi:10.1186/1750-1172-2-43. PMC 2211462. PMID 17980020.
- ↑ James, William; Berger, Timothy; Elston, Dirk (2005). Andrews' Diseases of the Skin: Clinical Dermatology. (10th ed.). Saunders. ISBN 0-7216-2921-0.
- 1 2 "Facts about Albinism", by Dr. Richard King et al.
- ↑ Giebel LB, Tripathi RK, King RA, Spritz RA (March 1991). "A tyrosinase gene missense mutation in temperature-sensitive type I oculocutaneous albinism. A human homologue to the Siamese cat and the Himalayan mouse". The Journal of Clinical Investigation. 87 (3): 1119–22. doi:10.1172/JCI115075. PMC 329910. PMID 1900309.
- 1 2 3 4 5 Online Mendelian Inheritance in Man Database, at Johns Hopkins University (see also Mendelian Inheritance in Man for more information about this source).
- ↑ "Ocular Manifestations of Albinism", by Dr. Mohammed O. Peracha, at eMedicine, 13 September 2005; retrieved 31 March 2007
- 1 2 3 4 "Albinism", by Dr. Raymond E. Boissy, Dr. James J. Nordlund, et al., at eMedicine, 22 August 2005; retrieved 31 March 2007
- ↑ Rundshagen U, Zühlke C, Opitz S, Schwinger E, Käsmann-Kellner B (February 2004). "Mutations in the MATP gene in five German patients affected by oculocutaneous albinism type 4". Human Mutation. 23 (2): 106–10. doi:10.1002/humu.10311. PMID 14722913.