Molecular basis of albinism: Mutations and polymorphisms of pigmentation genes associated with albinism

Albinism, caused by a deficiency of melanin pigment in the skin, hair, and eye (oculocutaneous albinism [OCA]), or primarily in the eye (ocular albinism [OA]), results from mutations in genes involved in the biosynthesis of melanin pigment. The lack of melanin pigment in the developing eye leads to fovea hypoplasia and abnormal routing of the optic nerves. These changes are responsible for the nystagmus, strabismus, and reduced visual acuity common to all types of albinism. Mutations in six genes have been reported to be responsible for different types of oculocutaneous and ocular albinism, including the tyrosinase gene (TYR) and OCA1 (MIM 203100), the OCA2 gene and OCA2 (MIM 203200), the tyrosinase-related protein-1 gene (TYRP1) and OCA3 (MIM 203290), the HPS gene and Hermansky-Pudlak syndrome (MIM 203300), the CHS gene (CHS1), and Chediak-Higashi syndrome (MIM 214500), and the X-linked ocular albinism gene and OA1 (MIM 300500). The function of only two of the gene products is known tyrosinase and tyrosinase-related protein-1 both of which are enzymes in the melanin biosynthetic pathway. Continued mutational analysis coupled with function/structure studies should aid our understanding of the function of the remaining genes and their role in albinism. Mutation and polymorphism data on these genes are available from the International Albinism Center Albinism Database web Site (http://www.cbc.umn.edu/tad).