OCA2 Gene

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This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/gene/oca2

OCA2 melanosomal transmembrane protein

genes

1. Introduction

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.

2. Health Conditions Related to Genetic Changes

2.1. Oculocutaneous albinism

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.

2.2. Angelman syndrome

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.

2.3. Prader-Willi syndrome

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.

More About This Health Condition

3. Other Names for This Gene

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

References

Bittel DC, Kibiryeva N, Talebizadeh Z, Butler MG. Microarray analysis ofgene/transcript expression in Prader-Willi syndrome: deletion versus UPD. J MedGenet. 2003 Aug;40(8):568-74.
Bittel DC, Kibiryeva N, Talebizadeh Z, Driscoll DJ, Butler MG. Microarrayanalysis of gene/transcript expression in Angelman syndrome: deletion versus UPD.Genomics. 2005 Jan;85(1):85-91.
Brilliant MH. The mouse p (pink-eyed dilution) and human P genes,oculocutaneous albinism type 2 (OCA2), and melanosomal pH. Pigment Cell Res. 2001Apr;14(2):86-93. Review.
Duffy DL, Montgomery GW, Chen W, Zhao ZZ, Le L, James MR, Hayward NK, MartinNG, Sturm RA. A three-single-nucleotide polymorphism haplotype in intron 1 ofOCA2 explains most human eye-color variation. Am J Hum Genet. 2007Feb;80(2):241-52.
Fridman C, Hosomi N, Varela MC, Souza AH, Fukai K, Koiffmann CP. Angelmansyndrome associated with oculocutaneous albinism due to an intragenic deletion ofthe P gene. Am J Med Genet A. 2003 Jun 1;119A(2):180-3.
Kerr R, Stevens G, Manga P, Salm S, John P, Haw T, Ramsay M. Identification ofP gene mutations in individuals with oculocutaneous albinism in sub-SaharanAfrica. Hum Mutat. 2000;15(2):166-72. Erratum in: Hum Mutat 2000;16(1):following 86.
Lewis RA. Oculocutaneous Albinism Type 2. 2003 Jul 17 [updated 2012 Aug 16].In: Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington,Seattle; 1993-2020. Available from http://www.ncbi.nlm.nih.gov/books/NBK1232/
Oetting WS, Garrett SS, Brott M, King RA. P gene mutations associated withoculocutaneous albinism type II (OCA2). Hum Mutat. 2005 Mar;25(3):323.
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.
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 butnot with haplotype of the hemizygous P allele. Am J Med Genet. 1997 Jul11;71(1):57-62.
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 oculocutaneousalbinism type 2 frequency in Japanese albino patients. J Invest Dermatol. 2003May;120(5):781-3.
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. PigmentCell Res. 2002 Jun;15(3):217-24. Erratum in: Pigment Cell Res. 2002Oct;15(5):400..

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Lily Guo

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Update Date: 24 Dec 2020

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