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Oculocutaneous albinism (OCA) is a heterogenous group of autosomal recessive disorders affecting melanin synthesis, characterised by congenital hypopigmentation of the skin, hair, and eyes. Reduced visual acuity, photophobia, iris transillumination, foveal hypoplasia, nystagmus, and an abnormal decussation of nerve fibres at the optic chiasm are common features.1 Ocular albinism (OA) shares the ocular features of OCA including the increased nerve fibre decussation at the optic chiasm. Patients affected by OA are often fairer in complexion than their unaffected siblings and have macromelanosomes present in the skin. In general, the skin hypopigmentation seen in OA is not as marked as that seen in OCA.
Key messages
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Oculocutaneous albinism comprises a heterogenous group of disorders of melanin metabolism resulting in a variable cutaneous phenotype that ranges from mild to severe depigmentation. Similarly, the ocular features generally vary in severity with degree of depigmentation. Visual evoked potential crossed asymmetry signifies an abnormal decussation of nerve fibres at the optic chiasm that is the hallmark of the disorder
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Molecular analysis of gene sequences may be an accurate tool for diagnosis and reveals that compound heterozygosity is common in all forms of oculocutaneous albinism
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Developmental events in the albino retina might be affected by abnormal melanin metabolism and could underlie the increased decussation at the optic chiasm, as well as the underdevelopment of the central retina
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Abnormal melanin metabolism might be responsible for other neurodevelopmental defects that underlie delayed visual maturation and nystagmus commonly seen in albinism
Melanogenesis
The tyrosinase gene regulates ocular and cutaneous melanin synthesis. Tyrosinase catalyses the first two steps in melanin synthesis. These are the oxidation of 1-tyrosine to 3,4-dihydroxyphenylalanine (DOPA) and its subsequent conversion to dopaquinone. Later steps in the melanin pathway, resulting in the formation of insoluble eumelanin, also involve tyrosinase. Phaeomelanin, a red-yellow pigment, is produced via an …