Contributor: Gordon K. Klintworth
Human oculocutaneous albinism is a group of inherited disorders caused by mutations in melanogenic genes (including  TYR, P gene, TYRP1, MATP). At least 10 distinct phenotypes of  oculocutaneous albinism with diminished pigmentation of the skin, hair, and eyes are recognized. They share an abnormal macula (macular hypoplasia [hypoplasia - macula] with abnormal vascular pattern), nystagmus, transparent irises, photophobia and a defective decussation of nerve fibers in the optic chiasm. Visual acuity is also decreased and factors that probably contribute to visual impairment include light scatter, light-induced damage to the retina, macular hypoplasia, and abnormal retinogeniculostriate projections. The types of oculocutaneous albinism are albinism - oculocutaneous type 1 (which has several subtypes [albinism - oculocutaneous type 1A, albinism - oculocutaneous type 1B, albinism - oculocutaneous type 1C, albinism - oculocutaneous type 1-TS], albinism - oculocutaneous type 2,  albinism - oculocutaneous type 3, albinism - oculocutaneous type 4, albinism - oculocutaneous type 5, albinism - oculocutaneous type 6A, albinism - oculocutaneous type 6B, and albinism - oculocutaneous type 7. The types of oculocutaneous albinism differ from each other with respect to certain clinical, biochemical, morphologic and genetic features. The prevalence of each type also varies in different populations. Except for autosomal dominant oculocutaneous albinism the other types of oculocutaneous albinism have an autosomal recessive mode of inheritance. Some types of oculocutaneous albinism result from genetic mutations that affect tyrosinase. The tyrosinase may be inactive, less active, or temperature-sensitive. Two types of oculocutaneous albinism have serious potentially lethal manifestations unrelated to melanin pigmentation. Individuals with oculocutaneous albinism type 6A  are susceptible bruising and bleeding and young children with oculocutaneous albinism type 6B are prone to infection. The aforementioned clearly does not reflect the entire story of oculocutaneous albinism as other incompletely characterized varieties of albinism have been documented. Other cases of oculocutaneous albinism have been observed in association with microcephaly, hypoplasia of the distal phalanx of several fingers of both hands and agenesis of the distal end of the big toe and infantile neuroaxonal dystrophy, but time will tell if these connections are more than fortuitous. The types of oculocutaneous albinism differ from each other with respect to certain clinical, biochemical, morphologic and genetic features. The prevalence of each type also varies in different populations. Except for  oculocutaneous type 7, which has an autosomal dominant mode of inheritance, the other types of oculocutaneous albinism have an autosomal recessive mode of inheritance. Based on the presence or absence of tyrosinase enzyme activity oculocutaneous albinism can be divided into tyrosinase negative [albinism - oculocutaneous tyrosinase negative] and tyrosinase positive oculocutaneous albinism [albinism - oculocutaneous tyrosinase positive]. Persons with tyrosinase-negative albinism lack pigment in the skin, hair, or eyes. In the other types of oculocutaneous albinism the quality of the melanin is abnormal. The aforementioned clearly does not reflect the entire story of oculocutaneous albinism as other incompletely characterized varieties of albinism have been documented. Other cases of oculocutaneous albinism have been observed in association with microcephaly, hypoplasia of the distal phalanx of several fingers of both hands and agenesis of the distal end of the big toe and infantile neuroaxonal dystrophy, but time will tell if these connections are more than fortuitous.