Hairbulb tyrosinase activity in oculocutaneous albinism

Abstract

HUMAN oculocutaneous albinism (OCA), characterised by hypopigmentation of skin, hair and eyes, represents a heterogeneous group of at least four distinct autosomal recessive disorders^1,2. Tyrosinase-negative OCA and tyrosinase-positive OCA are the two most common forms and can be separated by genetic and clinical features¹. Tyrosinase-negative albinos have no obvious pigment in their skin, hair or eyes, and their plucked hairbulbs form no visible pigment after prolonged incubation in L-tyrosine or L-3,4-dihydroxyphenylalanine (L-dopa). In contrast, tyrosinase-positive albinos have variable, albeit minimal, amounts of pigment in their skin, hair and eyes, and their plucked hairbulbs form large amounts of visible pigment after prolonged incubation in L-tyrosine or L-dopa. The two less common forms of OCA are Hermansky-Pudlak syndrome and yellow mutant OCA. The specific defect in each form of OCA is unknown, and analysis of the biochemical steps in the formation of melanin have been hindered by a lack of methods suitable for human studies. In this report, we describe an assay for quantifying tyrosinase activity in single human hairbulbs and give the results of the application of this technique to human oculocutaneous albinos.