Electron microscopic DOPA reaction test for oculocutaneous albinism

Oculocutaneous albinism (OCA) is an autosomal recessive disorder in which t he biosynthesis of melanin is reduced or absent in skin, hair and eyes, Tyr osinase-related OCA (OCA1) is caused by mutations in the tyrosinase gene, T yrosinase-negative OCA (OCA1A) is the most severe phenotype in which tyrosi nase catalytic activity is completely lost, resulting in no mature melanin pigment, Yellow OCA (OCA1B) varies from very little pigment associated with whitish-blond hair to nearly normal pigment with dark-blond hair and skin, We determined the tyrosinase activity in melanocytes by the electron micro scopic dihydroxyphenylalanine (EM-DOPA) reaction test using skin samples an d analyzed tyrosinase gene mutations in nine Japanese patients with OCA, In 18 alleles of nine patients, the OCA1A-associated mutations, P310insC, R77 Q and R278X, were found in seven, three and one alleles, respectively. Five patients who had these mutations in both alleles showed white hair, blue e yes and white skin and demonstrated no tyrosinase activity by the EM-DOPA r eaction test, Three patients who had no tyrosinase gene mutation showed tyr osinase activity and heterogeneous clinical features, One patient in whom o nly an R77Q OCA1A mutation was found in one allele demonstrated a reduced t yrosinase activity, indicating OCA1B, This patient had white hair at birth, but it had turned blond by the age of 1 year, These results indicate that the EM-DOPA reaction test provides clear information on the status of tyros inase activity which is essential for the identification of the disease sub type which in turn is important for the prognosis of patients with OCA.