Tyrosinase Activity in Melanocytes of Human Albinos

Abstract

Albinism is a condition that has attracted medical interest and description for many centuries. Until the past decade, however, efforts were largely confined to the publication of extensive pedigrees demonstrating the autosomal recessive inheritance of the trait and other reports illustrating the frequency of co-existing congenital anomalies-presumably also recessive. Histologic and histochemical studies were few and generally inadequate; these were based largely upon the work of Bruno Bloch who in 1917 demonstrated the formation of a pigment resembling melanin in normal epidermal melanocytes following incubation of skin sections in a solution of 1-dihydroxy-phenylalanine (1). The “dopa reaction” was an important discovery, not only in the study of the biosynthesis of melanin, but also as a useful histochemical method for the identification of melanocytes in tissues with a normal capacity for pigment formation. Albino tissues were shown, soon thereafter, not to possess dopa activity (2), and the erroneous assumption was subsequently made that melanocytes, as well as the melanogenic enzyme “dopa oxidase” which they contained, must be absent in this condition (3). In 1952, however, Becker, Jr. et al. (4) first announced that they had demonstrated “amelanotic” melanocytes in human albino skin using gold impregnation, and they concluded that the population density of such cells was the same as that found in normally pigmented skin. Their results have generally been accepted, although there is a considerable body of recent evidence indicating that the gold impregnated cells in question may not be melanocytes at all (5, 6). Other investigations have, however, now established the presence of melanocytes in albino tissues beyond any reasonable doubt. These cells have been identified in electron micrographs of hair follicles (7) and also of neoplasms, i.e., nevi and melanomas (8, 9).