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Genetics Home Reference: your guide to understanding genetic conditions
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OCA2

Reviewed October 2011

What is the official name of the OCA2 gene?

The official name of this gene is “oculocutaneous albinism II.”

OCA2 is the gene's official symbol. The OCA2 gene is also known by other names, listed below.

What is the normal function of the OCA2 gene?

The OCA2 gene (formerly called the P gene) provides instructions for making a protein called the P protein. This protein is located in melanocytes, which are specialized cells that produce a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color. Melanin is also found in the light-sensitive tissue at the back of the eye (the retina), where it plays a role in normal vision.

Although the exact function of the P protein is unknown, it is essential for normal pigmentation and is likely involved in the production of melanin. Within melanocytes, the P protein may transport molecules into and out of structures called melanosomes (where melanin is produced). Researchers believe that this protein may also help regulate the relative acidity (pH) of melanosomes. Tight control of pH is necessary for most biological processes.

How are changes in the OCA2 gene related to health conditions?

oculocutaneous albinism - caused by mutations in the OCA2 gene

More than 80 mutations in the OCA2 gene have been identified in people with oculocutaneous albinism type 2. People with this form of albinism often have light yellow, blond, or light brown hair; creamy white skin; light-colored eyes; and problems with vision. The most common OCA2 mutation is a large deletion in the gene, which is found in many affected individuals of sub-Saharan African heritage. Other OCA2 gene mutations, including changes in single DNA building blocks (base pairs) and small deletions, are more common in other populations. Mutations in the OCA2 gene disrupt the normal production of melanin, which reduces coloring of the hair, skin, and eyes and affects vision.

Angelman syndrome - associated with the OCA2 gene

The OCA2 gene is located in a region of chromosome 15 that is often deleted in individuals with Angelman syndrome. A loss of this gene does not cause the characteristic neurologic features of Angelman syndrome; however, people with this condition who are missing one copy of the OCA2 gene tend to have unusually light-colored hair and fair skin. Cells with only one copy of the OCA2 gene make a reduced amount of P protein compared with cells with two functional copies of this gene, which affects the coloring of the hair and skin.

A small percentage of people with Angelman syndrome also have oculocutaneous albinism type 2. This condition occurs when people have two nonfunctional copies of the OCA2 gene in each cell. In addition to a deletion in chromosome 15 that removes one copy of the OCA2 gene, these individuals have a mutation in the OCA2 gene on the other copy of chromosome 15. As a result, cells make little or no functional P protein. A lack of P protein disrupts the production of melanin, leading to the characteristic features of albinism.

Prader-Willi syndrome - associated with the OCA2 gene

The region of chromosome 15 containing the OCA2 gene is often deleted in individuals with Prader-Willi syndrome. A loss of this gene does not cause intellectual disability and the other characteristic features of Prader-Willi syndrome; however, people with this condition who are missing one copy of the OCA2 gene tend to have unusually light-colored hair and fair skin. Cells missing a copy of the OCA2 gene make less P protein than cells with two functional copies of the gene, which affects the coloring of the hair and skin.

Oculocutaneous albinism type 2 also occurs in a small number of people with Prader-Willi syndrome. This condition occurs when people have two nonfunctional copies of the OCA2 gene in each cell. In addition to a deletion in chromosome 15 that removes one copy of the OCA2 gene, these individuals have a mutation in the OCA2 gene on the other copy of chromosome 15. As a result, cells make little or no functional P protein. A lack of P protein disrupts the production of melanin, leading to the characteristic features of albinism.

Where is the OCA2 gene located?

Cytogenetic Location: 15q

Molecular Location on chromosome 15: base pairs 27,754,872 to 28,099,339

The OCA2 gene is located on the long (q) arm of chromosome 15.

The OCA2 gene is located on the long (q) arm of chromosome 15.

More precisely, the OCA2 gene is located from base pair 27,754,872 to base pair 28,099,339 on chromosome 15.

See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.

Where can I find additional information about OCA2?

You and your healthcare professional may find the following resources about OCA2 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the OCA2 gene or gene products?

  • BOCA
  • Melanocyte-specific transporter protein
  • oculocutaneous albinism II (pink-eye dilution homolog, mouse)
  • PED
  • P gene
  • P_HUMAN
  • Pink-eyed dilution protein homolog

See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What glossary definitions help with understanding OCA2?

acidity ; albinism ; cell ; chromosome ; deletion ; disability ; DNA ; gene ; melanin ; melanocytes ; mutation ; neurologic ; pH ; pigment ; pigmentation ; protein ; retina ; syndrome ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

References

  • Bittel DC, Kibiryeva N, Talebizadeh Z, Butler MG. Microarray analysis of gene/transcript expression in Prader-Willi syndrome: deletion versus UPD. J Med Genet. 2003 Aug;40(8):568-74. (http://www.ncbi.nlm.nih.gov/pubmed/12920063?dopt=Abstract)
  • Bittel DC, Kibiryeva N, Talebizadeh Z, Driscoll DJ, Butler MG. Microarray analysis of gene/transcript expression in Angelman syndrome: deletion versus UPD. Genomics. 2005 Jan;85(1):85-91. (http://www.ncbi.nlm.nih.gov/pubmed/15607424?dopt=Abstract)
  • Brilliant MH. The mouse p (pink-eyed dilution) and human P genes, oculocutaneous albinism type 2 (OCA2), and melanosomal pH. Pigment Cell Res. 2001 Apr;14(2):86-93. Review. (http://www.ncbi.nlm.nih.gov/pubmed/11310796?dopt=Abstract)
  • Duffy DL, Montgomery GW, Chen W, Zhao ZZ, Le L, James MR, Hayward NK, Martin NG, Sturm RA. A three-single-nucleotide polymorphism haplotype in intron 1 of OCA2 explains most human eye-color variation. Am J Hum Genet. 2007 Feb;80(2):241-52. Epub 2006 Dec 20. (http://www.ncbi.nlm.nih.gov/pubmed/17236130?dopt=Abstract)
  • Fridman C, Hosomi N, Varela MC, Souza AH, Fukai K, Koiffmann CP. Angelman syndrome associated with oculocutaneous albinism due to an intragenic deletion of the P gene. Am J Med Genet A. 2003 Jun 1;119A(2):180-3. (http://www.ncbi.nlm.nih.gov/pubmed/12749060?dopt=Abstract)
  • Gene Review: Oculocutaneous Albinism Type 2 (http://www.ncbi.nlm.nih.gov/books/NBK1232)
  • Kerr R, Stevens G, Manga P, Salm S, John P, Haw T, Ramsay M. Identification of P gene mutations in individuals with oculocutaneous albinism in sub-Saharan Africa. Hum Mutat. 2000;15(2):166-72. Erratum in: Hum Mutat 2000;16(1):following 86. (http://www.ncbi.nlm.nih.gov/pubmed/10649493?dopt=Abstract)
  • NCBI Gene (http://www.ncbi.nlm.nih.gov/gene/4948)
  • Oetting WS, Garrett SS, Brott M, King RA. P gene mutations associated with oculocutaneous albinism type II (OCA2). Hum Mutat. 2005 Mar;25(3):323. (http://www.ncbi.nlm.nih.gov/pubmed/15712365?dopt=Abstract)
  • Saitoh S, Oiso N, Wada T, Narazaki O, Fukai K. Oculocutaneous albinism type 2 with a P gene missense mutation in a patient with Angelman syndrome. J Med Genet. 2000 May;37(5):392-4. (http://www.ncbi.nlm.nih.gov/pubmed/10905897?dopt=Abstract)
  • Spritz RA, Bailin T, Nicholls RD, Lee ST, Park SK, Mascari MJ, Butler MG. Hypopigmentation in the Prader-Willi syndrome correlates with P gene deletion but not with haplotype of the hemizygous P allele. Am J Med Genet. 1997 Jul 11;71(1):57-62. (http://www.ncbi.nlm.nih.gov/pubmed/9215770?dopt=Abstract)
  • Suzuki T, Miyamura Y, Matsunaga J, Shimizu H, Kawachi Y, Ohyama N, Ishikawa O, Ishikawa T, Terao H, Tomita Y. Six novel P gene mutations and oculocutaneous albinism type 2 frequency in Japanese albino patients. J Invest Dermatol. 2003 May;120(5):781-3. (http://www.ncbi.nlm.nih.gov/pubmed/12713581?dopt=Abstract)
  • Toyofuku K, Valencia JC, Kushimoto T, Costin GE, Virador VM, Vieira WD, Ferrans VJ, Hearing VJ. The etiology of oculocutaneous albinism (OCA) type II: the pink protein modulates the processing and transport of tyrosinase. Pigment Cell Res. 2002 Jun;15(3):217-24. Erratum in: Pigment Cell Res. 2002 Oct;15(5):400.. (http://www.ncbi.nlm.nih.gov/pubmed/12028586?dopt=Abstract)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: October 2011
Published: July 27, 2015