Oculocutaneous albinism is a genetically heterogeneous congenital disorder characterized by decreased or absent pigmentation in the hair, skin, and eyes. The term 'albinism' includes specific ocular changes that are the results of reduced amounts of melanin in the developing eye; these abnormalities in the eye and optic system are specific and necessary for the diagnosis. Aside from decreased pigment in the iris and retina, optic changes include decreased visual acuity, misrouting of the optic nerves at the chiasm, and nystagmus (King et al., 2001).
Although OCA caused by mutations in the TYR gene was classically known as 'tyrosinase-negative' OCA, Tripathi et al. (1992) noted that some patients with 'tyrosinase-positive' OCA may indeed have TYR mutations resulting in residual enzyme activity. These patients can be classified as having OCA1B.
Genetic Heterogeneity of Oculocutaneous Albinism
OCA1, caused by mutations in the TYR gene, is divided clinically into 2 types: type IA, OCA1A, characterized by complete lack of tyrosinase activity due to production of an inactive enzyme, and type IB (OCA1B; 606952), characterized by reduced activity of tyrosinase. OCA2 (203200), OCA3 (203290), and OCA4 (606574) are somewhat milder forms of the disorder, caused by mutations in the OCA2 (611409), TYRP1 (115501), and MATP (SLC45A2; 606202) genes, respectively. OCA5 (615312) has been mapped to chromosome 4q24. OCA6 (see 113750) is caused by mutation in the SLC24A5 gene (609802). OCA7 (615179) is caused by mutation in the LRMDA gene (614537). OCA8 (619165) is caused by mutation in the DCT gene (191275).
See also ocular albinism (OA1; 300500), which is restricted phenotypically to ocular involvement only. [from
OMIM]