Aniridia

Aniridia is an eye disorder characterized by a complete or partial absence of the colored part of the eye (the iris). These iris abnormalities may cause the pupils to be abnormal or misshapen. Aniridia can cause reduction in the sharpness of vision (visual acuity) and increased sensitivity to light (photophobia).

People with aniridia can also have other eye problems. Increased pressure in the eye (glaucoma) typically appears in late childhood or early adolescence. Clouding of the lens of the eye (cataracts), occur in 50 percent to 85 percent of people with aniridia. In about 10 percent of affected people, the structures that carry information from the eyes to the brain (optic nerves) are underdeveloped. Individuals with aniridia may also have involuntary eye movements (nystagmus) or underdevelopment of the region at the back of the eye responsible for sharp central vision (foveal hypoplasia). Many of these eye problems contribute to progressive vision loss in affected individuals. The severity of symptoms is typically the same in both eyes.

Rarely, people with aniridia have behavioral problems, developmental delay, and problems detecting odors.

How common is aniridia?

Aniridia occurs in 1 in 50,000 to 100,000 newborns worldwide.

What genes are related to aniridia?

Aniridia is caused by mutations in the PAX6 gene. The PAX6 gene provides instructions for making a protein that is involved in the early development of the eyes, brain and spinal cord (central nervous system), and the pancreas. Within the brain, PAX6 is involved in the development of a specialized group of brain cells that process smell (the olfactory bulb). The PAX6 protein attaches (binds) to specific regions of DNA and regulates the activity of other genes. On the basis of this role, the PAX6 protein is called a transcription factor. Following birth, the PAX6 protein regulates several genes that likely contribute to the maintenance of different eye structures.

Mutations in the PAX6 gene result in the production of a nonfunctional PAX6 protein that is unable to bind to DNA and regulate the activity of other genes. A lack of functional PAX6 protein disrupts the formation of the eyes during embryonic development.

Read more about the PAX6 gene.

How do people inherit aniridia?

Aniridia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

In approximately two-thirds of cases, an affected person inherits the mutation from one affected parent. The remaining one-third of cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

Where can I find information about treatment for aniridia?

These resources address the management of aniridia and may include treatment providers.

• Gene Review: Aniridia

You might also find information on treatment of aniridia in Educational resources and Patient support.

Where can I find additional information about aniridia?

You may find the following resources about aniridia helpful. These materials are written for the general public.

• MedlinePlus - Health information
• Health Topic: Eye Diseases
• Additional NIH Resources - National Institutes of Health
• National Eye Institute: Diagram of the Eye
• Educational resources - Information pages (8 links)
• Patient support - For patients and families (3 links)

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

• Gene Reviews - Clinical summary
• Gene Tests - DNA tests ordered by healthcare professionals
• ClinicalTrials.gov - Linking patients to medical research
• PubMed - Recent literature
• Online Books - Medical and science texts
• Scriver's Online Metabolic and Molecular Bases of Inherited Disease (OMMBID): Transcription Factors in Eye Disease and Ocular Development
• OMIM - Genetic disorder catalog

What if I still have specific questions about aniridia?

• See How can I find a genetics professional in my area? in the Handbook.
• Ask the Genetic and Rare Diseases Information Center.
• Submit your question to Ask the Geneticist.

Where can I find general information about genetic conditions?

The Handbook provides basic information about genetics in clear language.

• What does it mean if a disorder seems to run in my family?
• What are the different ways in which a genetic condition can be inherited?
• If a genetic disorder runs in my family, what are the chances that my children will have the condition?
• Why are some genetic conditions more common in particular ethnic groups?

These links provide additional genetics resources that may be useful.

• Genetics and health
• Resources for Patients and Families
• Resources for Health Professionals

What glossary definitions help with understanding aniridia?

autosomal ; autosomal dominant ; cataract ; cell ; central nervous system ; developmental delay ; DNA ; embryonic ; gene ; glaucoma ; hypoplasia ; involuntary ; mutation ; nervous system ; new mutation ; nystagmus ; olfactory bulb ; optic nerve ; pancreas ; photophobia ; protein ; pupil ; sensitivity ; symptom ; transcription ; transcription factor ; visual acuity

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

References

These sources were used to develop the Genetics Home Reference condition summary on aniridia.

• Chao LY, Huff V, Strong LC, Saunders GF. Mutation in the PAX6 gene in twenty patients with aniridia. Hum Mutat. 2000;15(4):332-9. PubMed citation
• Lee H, Khan R, O'Keefe M. Aniridia: current pathology and management. Acta Ophthalmol. 2008 Nov;86(7):708-15. Epub 2008 Oct 6. Review. PubMed citation
• Robinson DO, Howarth RJ, Williamson KA, van Heyningen V, Beal SJ, Crolla JA. Genetic analysis of chromosome 11p13 and the PAX6 gene in a series of 125 cases referred with aniridia. Am J Med Genet A. 2008 Mar 1;146A(5):558-69. PubMed citation