Minimal pigment: a new type of oculocutaneous albinism.

Minimal pigment, a new type of oculocutaneous albinism (OCA), is described. At birth, affected individuals had no skin or eye pigment, and white hair and blue irides, but minimal amounts of pigment developed in the iris during the first decade of life. They had no measurable hairbulb tyrosinase activity. A characteristic and unusual pattern of parental activity was found in each of three families studied, with one parent having normal and the other parent having abnormally low tyrosinase activity. The melanocyte ultrastructure was normal and variations in premelanosomal pigmentation correlated with tyrosinase activity. This clinical and biochemical pattern has not been seen in any of the previously described types of OCA. The biochemical defect in minimal pigment OCA is unknown.