Human oculocutaneous albinism caused by single base insertion in the tyrosinase gene.

Tyrosinase-negative oculocutaneous albinism (OCA) is an inborn error of metabolism, characterized by a complete lack of melanin pigments in the eyes and skin. We have isolated and characterized the tyrosinase gene of one affected child (S.S.) with tyrosinase-negative OCA. Sequence analysis reveals a single-base insertion in the exon 2 that shifts the reading frame and introduces a premature termination signal (TGA codon) after the amino acid residue 298. Functional analysis of the mutated gene indicates that such a truncated tyrosinase lacking one potential copper-binding region is catalytically inactive. We therefore conclude that the albino phenotype of the patient S.S. is a consequence of the inactive tyrosinase caused by the nonsense mutation in the tyrosinase gene.