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Aniridia
Aniridia is the absence of the iris, usually involving both eyes. It can be congenital or caused by a penetrant injury. Isolated aniridia is a congenital disorder which is not limited to a defect in iris development, but is a panocular condition with macular and optic nerve hypoplasia, cataract, and corneal changes. Vision may be severely compromised and the disorder is frequently associated with a number of ocular complications: nystagmus, amblyopia, buphthalmos, and cataract.〔 Aniridia in some individuals is associated with kidney nephroblastoma (Wilms tumor), genitourinary anomalies, or intellectual disability and cerebellar ataxia (Gillespie syndrome), resulting in the WAGR syndrome.
==PAX6==
The AN2 region of the short arm of chromosome 11 (11p13) includes the PAX6 gene (named for its PAired boX status), whose gene product helps regulate a cascade of other genetic processes involved in the development of the eye (as well as other nonocular structures). This PAX6 gene is around 95% similar to the pax gene found in zebrafish, a creature whose ancestors diverged from human evolutionary development around 400 million years ago. Thus the PAX6 gene is highly conserved across evolutionary lineages.
Defects in the PAX6 gene cause aniridia-like ocular defects in mice (as well as ''Drosophila''). Aniridia is a heterozygous disorder, meaning that only one of the two chromosome 11 copies is affected. When both copies are altered (homozygous condition), the result is a uniformly fatal condition with near complete failure of entire eye formation. In 2001, two cases of homozygous aniridia patients were reported; the fetuses died prior to birth and had severe brain damage. In mice, homozygous ''small eye'' defect (mouse Pax-6) leads to loss of the eyes and nose and the murine fetuses suffer severe brain damage.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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