Albinism



Albinism is a rare, hereditary (AR) metabolic disorder due to a defect in the enzyme tyrosinase. The disorder results in a partial or complete absence of melanin. It can occur in humans, animals and plants.

Albinism is phenotypically divided into tyrosinase-positive and tyrosinase-negative, genotypically into OCA 1 to OCA 3.



Biochemical essence


Melanin is a pigment synthesized in the melanosomes (derived from the Golgi apparatus) of melanocytes (epidermal cells) from the amino acid tyrosine (see figure). This enzyme has dual activity: tyrosine hydroxylase and dopaoxidase. Under normal circumstances, tyrosine is first hydroxylated by tyrosinase to DOPA – i.e. 3,4-dihydroxyphenylalanine, and then oxidized to dopaquinone. The next enzyme in the sequence catalyzes the tautomerization of the intermediate. The final product subsequently polymerizes into eumelanin.

If there is a defect in the region of the gene encoding tyrosinase (facial protein), the metabolic pathway cannot proceed and the pigment is not synthesized.

OCA 1
Mutation of the structural gene for tyrosinase.


 * OCA 1A (tyrosinase negative) – complete absence of tyrosinase


 * OCA 1B (yellow albinism - xanthoalbinism) - weak enzyme activity in the hair

OCA 2
Mutation of the structural gene for P protein (melanosomal transmembrane protein with a transport function – tyrosine transport), the most common type of albinism.

OCA 3
The so-called brown albinism – mutation of the gene for TRP-1, is known only in blacks Albinism is also often accompanied by phenylketonuria (AR disease, caused by a defect in the enzyme phenylalanine hydroxylase ).

Total albinism
Albinism is manifested by white skin and hair, red or light blue eyes. The skin is very sensitive to UV radiation and at the same time there is a higher risk of developing skin tumors. It also causes faster aging of the skin.

Partial albinism
This is partial albinism manifested only locally, for example on areas of the skin and areas of hair. The eyes are not affected in this type.

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