Albinism oculocutaneous tyrosinase-positiveE70.3

Author:Prof. Dr. med. Peter Altmeyer

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Last updated on: 23.07.2024

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Synonym(s)

OCA2; Oculocutaneous albinism Tyrosinase-positive; OMIM 203200; Tyrosinase-positive oculocutaneous albinism

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DefinitionThis section has been translated automatically.

Oculocutaneous albinism with autosomal recessive inherited defects of melanin synthesis (tyrosinase activity normal) with greatly reduced but not completely absent pigmentation. Another phenotype of OCA2 occurs predominantly in the black African population or their descendants and is called brown albinism ( brown African albinism).

Occurrence/EpidemiologyThis section has been translated automatically.

OCA2 occurs predominantly in coloured people of African descent. A recognized association exists between OCA2, the hypopigmentations of Prader-Willi syndrome and Angelman syndrome. In both diseases, as in OCA2, the genetic defect on chromosome 15 is located in the q region.

EtiopathogenesisThis section has been translated automatically.

It is caused by mutations in the P gene(OCA2 gene). > More than 150 mutations are now known. The gene codes for the protein that plays a key role in melanin biosynthesis as a transporter protein for melanosomal proteins such as TYR and TYRP1.

The encoded "Melanosomal Transmembrane Protein" contributes to a melanosome-specific anion (chloride) current that modulates melanosomal pH for optimal tyrosinase activity required for melanogenesis and melanosome maturation.

Remark: Intracellular ion channels are essential regulators of organellar and cellular functions. A chloride-selective anion conductance mediated by OCA2, which is required for melanin production, has been identified in skin and eye melanosomes. Expression of OCA2 increases the pH of the organelle, suggesting that the chloride channel regulates melanin synthesis by modulating melanosome pH. This finding suggests that a melanosomal anion channel exists that requires OCA2 and is essential for skin and eye pigmentation (Bellono NW et al. 2014).

Clinical featuresThis section has been translated automatically.

At birth white hair, white skin; with increasing age slight pigmentation (hair becomes blond or reddish) Often numerous ephelids, possibly melanocytic naevi. In advanced age increased rate of UV-induced malignant epithelial tumours(basal cell carcinoma, spinocellular carcinoma). Grey-blue to light brown translucent iris, ocular fundus depigmented. Moderate nystagmus and photophobia, slight visual impairment. In patients of African descent, large melanocytic nevi and lentigines are frequently found in UV-exposed skin.

DiagnosisThis section has been translated automatically.

Positive tyrosinase detection in the skin. Pigmentation of hair roots when incubated in tyrosine. Electron microscopic: maturation of melanosomes up to stage III.

Complication(s)This section has been translated automatically.

Risk of carcinoma development at the base of actinic damage (see below albinism, tyrosinase-negative oculocutaneous).

TherapyThis section has been translated automatically.

S.u. Albinism.

LiteratureThis section has been translated automatically.

  1. Baxter LL, Pavan WJ (2002) The oculocutaneous albinism type IV gene Matp is a new marker of pigment cell precursors during mouse embryonic development. Mech Dev 116: 209-212

  2. Bellono NW et al. (2014) An intracellular anion channel critical for pigmentation. Elife: e04543).

  3. Brilliant MH (2001) The mouse p (pink-eyed dilution) and human P genes, oculocutaneous albinism type 2 (OCA2), and melanosomal pH. Pigment Cell Res 14:86-93.

  4. Kamaraj B et al.(2014) Mutational analysis of oculocutaneous albinism: a compact review. Biomed Res Int doi: 10.1155/2014/905472.
  5. King RA et al. (2003) Tyrosinase gene mutations in oculocutaneous albinism 1 (OCA1): definition of the phenotype. Hum Genet 113: 502-513
  6. Kubasch A et al. (2017) Oculocutaneous and ocular albinism. Dermatology 68: 867-875
  7. Nakamura E et al. (2002) A novel mutation of the tyrosinase gene causing oculocutaneous albinism type 1 (OCA1). J Dermatol Sci 28: 102-105
  8. Oetting WS et al. (2003) Oculocutaneous albinism type 1: the last 100 years. Pigment Cell Res 16: 307-311
  9. Okulicz JF et al (2003) Oculocutaneous albinism. J Eur Acad Dermatol Venereol 17: 251-256
  10. Rundshagen U et al. (2003) Mutations in the MATP gene in five German patients affected by oculocutaneous albinism type 4. Hum Mutat 23: 106-110
  11. Terenziani M et al. (2003) Amelanotic melanoma in a child with oculocutaneous albinism. Med Pediatr Oncol 41: 179-180

Authors

Last updated on: 23.07.2024

Author: Prof. Dr. med. Peter Altmeyer