Hairbulb tyrosinase activity in oculocutaneous albinism: suggestions for pathway control and block location.

Hairbulb tyrosinase activity was determined in 72 individuals with five types of oculocutaneous albinism (OCA) and 64 obligate heterozygotes. Type IA (tyrosinase-negative) and type IB (yellow mutant) individuals had low or no measurable tyrosinase activity, and heterozygotes for these two types could be detected with this assay. Type II (tyrosinase-positive) individuals had moderate to high activity, and the heterozygotes for this type could not be detected. Type III (minimal pigment) individuals had low activity, and heterozygote levels were useful in detecting this type of OCA. Type VI (Hermansky-Pudlak syndrome) individuals had moderate to no measurable activity, and heterozygotes for this type could not be detected. The implication of the tyrosinase assay results in light of the phenotype and the possible location of the pigment block in these forms of OCA are discussed.