[Human oculocutaneous albinism. From clinical observation to molecular biology].

Human oculocutaneous albinism (OCA) is a heritable metabolic defect transmitted as an autosomal recessive trait and characterized by a hypopigmentation of skin, hair and eyes. This defect is mainly due to an altered or absence of tyrosinase activity, the key enzyme of eu-and pheo-melanin synthesis. It is a seldom condition in white peoples but more frequent in Africans and in Afro-Americans. Albinos, especially in tropical settings, have high prevalence of solar keratosis and squamous cell carcinoma. Ocular defects characteristics of OCA are photobia, nystagmus and decreased visual acuity. Two forms of OCA have been distinguished in 1970 on the basis of their genetic, clinical, biochemical and ultrastructural characteristics: type I i. e. tyrosinase negative and type II i. e. tyrosinase positive. Actually 10 forms are described. Human tyrosinase gene has been mapped to chromosome 11 (q14-21) and cloned. It is formed by 5 exons. Several different human tyrosinase gene mutations have been identified in patients with type I-A OCA. Non sense, misense and frameshift mutations result in altered or absence of tyrosinase activity.