Albinism

Abstract

Albinism comprises a heterogeneous group of inherited disorders characterized by the reduction or total absence of pigment from the eye, hair, and skin. All the currently known types of albinism are inherited in an autosomal recessive fashion with the exception of Nettleship-Falls ocular albinism, which is X-linked recessive. Albinism has been classified by the degree and the distribution of hypopigmentation as total versus partial,1 and ocular versus oculocutaneous types. As the molecular genetic understanding of disorders of pigmentation has improved,2,3 we can now classify oculocutaneous albinism (OCA) more accurately with regard to the specific genetic defect in each clinical subtype (Table 45.1).The ophthalmologic findings in all forms of albinism are consistent, though variable in severity. Signs include nystagmus, hypopigmentation of the uveal tract and retinal pigment epithelium (RPE), iris transillumination, foveal hypoplasia, and abnormal decussation of optic nerve fibers at the chiasm. Strabismus and high refractive errors are common. Symptoms include decreased visual acuity, reduced or absent stereoacuity, and photophobia.Albinoidism refers to the reduction of ocular and cutaneous pigmentation without visual system abnormalities.Albinism results from the defective production of melanin from tyrosine through a complex pathway of metabolic reactions that were worked out partially by Raper4 early in the 20th century. Melanogenesis is a complicated pathway involving enzymes and proteins coded for by genes on a number of chromosomes.