Albinism oculocutaneous tyrosinase-positive E70.3

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 21.06.2022

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

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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).

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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.

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Underlying mutations in the P gene (OCA2 gene). > 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 protein maintains the acidic pH in melanosomes.

Clinical features
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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.

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

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

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S.u. Albinism.

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Last updated on: 21.06.2022