Albinism oculocutaneous (overview) E70.3

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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Synonym(s)

OCA; OCA3; OCA4; OCA5; OCA6; OCA7; Oculocutaneous albinism

Definition
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Group of genetically different, almost exclusively autosomal-recessive inherited metabolic diseases characterized by diffuse hypopigmentation in skin, hair and eyes; caused by partial or complete absence of melanin in the melanocytes The number of epidermal and follicular melanocytes is normal.

Classification
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7 types are differentiated based on molecular differences:

  • OCA 1 (Tyrosinase-negative OCA): Based on reduced or no tyrosinase activity; about 80 mutations in the tyrosinase gene (TYR) have been described. OCA 1 is also known as yellow albinism.
  • OCA 2 (tyrosinase-positive OCA): Based on mutations in the P gene; the role of the P protein is still unclear; regulation of the pH in the melanosomes? OCA 2 is also known as brown albinism or brown African albinism.
  • OCA 3 (OMIM 203290)- Red albinism: Caused by mutations in the tyrosinase-related protein gene (TYRP1 gene; Tyrp1 protein is a melanocyte-specific gene product involved in eumelanin synthesis).
  • OCA 4 (OMIM 606574): Caused by mutations of a membrane-associated transporter protein (MATP) gene encoding a transport protein for melanin precursors. Common in Korea and Japan.
  • OCA 5: OCA 5 has been described in a Pakistani family (white skin, golden hair and eye symptoms). The gene is still unknown; it has been assigned to chromosome 4q24, a gene locus that probably codes for lysosomal proteins.
  • OCA 6-7: Like OCA 4, OCA 6 is a mutation of a transporter protein (chromosome 15q21.1). In OCA 7 a mutation was found in the gene " C10orf11" located on chromosome 10q 22.2-22.3 which codes for a protein that is important for melanocyte differentiation. Further entities are expected in the future.

Occurrence/Epidemiology
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Most common inherited disease with diffuse hypomelanosis of the skin. The prevalence is estimated at 1:17,000 - 1:20,000 inhabitants; for some African strains it is 1:1,500 inhabitants.

For the tyrosine negative subtype OCA1 (affects 40% of all forms of albnism) the estimated prevalence in the European population is 1:40,000.

The tyrosine-positive subtype OCA2 (affects 50% of all forms of albnism worldwide) occurs predominantly in the African population. In South Africa and Tanzania, the prevalence is 1:1,400 to 1:10,000 inhabitants (cited in Kubash A 2017)

Etiopathogenesis
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All types of oculocutaneous albinism (OCA) are based on an autosomal recessive inheritance mechanism, except for a few families with autosomal dominant OCA. The disease is caused by mutations that directly affect the tyrosine singing TYR, or genes of proteins that regulate the processing of the copper-containing enzyme tyrosinase and the biosynthesis of melanin in melanosomes and the secretion of mature melanosomes into the epidermis (cited in Kubasch A et al. 2017).

Therapy
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Despite various preclinical approaches (e.g. tyrosinase gene transfer, etc.), the only therapeutic options remaining are strict physical and chemical sun protection. Regular dermatological check-ups are necessary (incidences of basal cell carcinoma and squamous cell carcinoma are significantly increased, but not of malignant melanoma).

Note(s)
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Oculocutaneous albinism can be associated with some rare syndromes:

Literature
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  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. Kamaraj B et al(2014) Mutational analysis of oculocutaneous albinism: a compact review. Biomed Res Int doi: 10.1155/2014/905472.
  3. King RA et al (2003) Tyrosinase gene mutations in oculocutaneous albinism 1 (OCA1): definition of the phenotype. Hum Genet 113: 502-513
  4. Kubasch A et al (2017) Oculocutaneous and ocular albinism. Dermatologist 68: 867-875
  5. King RA et al (2003) MC1R mutations modify the classic phenotype of oculocutaneous albinism type 2 (OCA2). At J Hum Genet 73: 638-645
  6. Nakamura E et al (2002) A novel mutation of the tyrosinase gene causing oculocutaneous albinism type 1 (OCA1). J Dermatol Sci 28: 102-105
  7. Oetting WS et al (2003) Oculocutaneous albinism type 1: the last 100 years. Pigment Cell Res 16: 307-311
  8. Okulicz JF et al (2003) Oculocutaneous albinism. J Eur Acad Dermatol Venereol 17: 251-256
  9. Rundshagen U et al (2003) Mutations in the MATP gene in five German patients affected by oculocutaneous albinism type 4 Hum mutation 23: 106-110
  10. Terenziani M et al (2003) Amelanotic melanoma in a child with oculocutaneous albinism. Med Pediatr Oncol 41: 179-180

Disclaimer

Please ask your physician for a reliable diagnosis. This website is only meant as a reference.

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Last updated on: 29.10.2020