page_title: Aniridia
section_title: PAX6
hierarchical_section_title: Aniridia / PAX6
caption_attribution_description: Phenotypic expression of aniridia with PAX6 gene mutation. The aniridic probands showed typical features of sclerocornea with nystagmus in proband 28–1 (A); Foveal hypoplasia in proband 27–1 (B); Ptosis, microcornea with dislocated cataractous lens in proband 10–1 (C); Ectopia lentis in proband 16–1 (D).
context_page_description: 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 occurs as part of a syndrome, such as WAGR syndrome, or Gillespie syndrome.
context_section_description: 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 non-ocular 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.
caption: Phenotypic expression of aniridia with PAX6 gene mutation. The aniridic  probands showed typical features of sclerocornea with nystagmus in proband 28–1 (A); Foveal hypoplasia in  proband 27–1 (B);  Ptosis, microcornea with dislocated cataractous lens in proband 10–1 (C); Ectopia lentis in  proband 16–1 (D).
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