Albinism

Genetic abnormalities of the melanin pigment system in which the synthesis of melanin is reduced or absent are called albinism. The reduction in melanin synthesis can involve the skin, hair follicle, and eye, resulting in oculocutaneous albinism (OCA), or can be localized primarily to the eye, resulting in ocular albinism (OA). At least nine types of albinisms have been described. Most types are autosomal recessive in inheritance, but one type of OA is X-linked recessive in inheritance. As can be seen from the table, some skin, hair, and eye melanin is found in most types of albinism; total absence of cutaneous and ocular melanin is found only in type IA (tyrosine-negative) OCA. Albinism is a common genetic condition. Approximately 1 in 17,000 individuals in the United States had OCA, with type IA (tyrosinase-negative) and type II (tyrosine-positive) being the most prevalent. The other types of OCA are infrequent or rare. The prevalence of OA is not well established but is thought to be considerably less than that of OCA. More than 1 per cent of the population are heterozygous for a gene producing albinism.