Definition: a disorder characterized by deficiency of pigment in skin, hair, and eyes, photophobia, nystagmus, and decreased visual acuity; there are two types: tyrosinase negative [MIM*203100] in which there is absence of tyrosinase, and tyrosinase positive [MIM*203200] in which normal tyrosinase cannot enter pigment cells; the compound heterozygote is normal so the two forms are not allelic. There are several forms of autosomal recessive inheritance: type IA is characterized by absence of tyrosinase with life-long complete absence of melanin, marked photophobia, and nystagmus, caused by mutation in the tyrosinase gene (TYR) on chromosome 11q. Type II has normal tyrosinase activity and is the most common; hair color darkens and nevi and freckles develop; caused by mutation in the oculocutaneous abinism gene (OCA2) on 15q. Type III is characterized by absent tyrosinase but pigmentation of the iris in the first decade; caused by mutation in the tyrosine-related protein-1gene (TYRP1) on 9p. Type IV is found in Africans with normal tyrosinase and type V is associated with red hair. Type VI is synonymous to Hermansky-Pudlak syndrome [MIM*203300], with low to absent tyrosinase and hemorrhage due to platelet deficiency, caused by mutation in the Hermansky-Pudlak gene (HPS) on 10q.
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