Aniridia, meaning “without iris”, is a rare genetic disorder affecting vision, characterised by incomplete formation of the eye iris (the coloured part of the eye that surrounds the black pupil).
It may also cause other parts of the eye to be under-developed such as the optic nerve and the macula (the central part of the retina).
People with aniridia may also develop other eye conditions. Aniridia and these associated conditions affect everyone differently. So while some people with aniridia are partially sighted or blind, others may have near normal sight.
Aniridia is congenital (present at birth) and is caused by a disfunction of the PAX6 gene, situated on the 11^th chromosome, that causes the eye to stop developing too early.
The disease is most often inherited as an autosomal dominant trait (familial aniridia). One in three cases may instead result from a de novo mutation, that is a genetic mutation that occurs in a child whose parents are not affected by the disease (sporadic aniridia).
Aniridia affects 1 : 40,000 to 1 : 100,000 people , and affects males and females equally.
People with aniridia may also experience secondary conditions; most people with aniridia will not develop all of these and some may not develop any at all.
- Photophobia: sensitivity to light that can dazzle and make it difficult to see. It can also cause discomfort, pain or headaches;
- Nystagmus: constant involuntary movement of the eyeball;
- Glaucoma: elevated pressure in the eyeball that may permanently damage the optic nerve;
- Cataracts: clouding of the lens;
- Keratopathy: a variety of conditions that affect the cornea, the transparent front part of the eye that covers the iris and pupil, due to a deficiency of limbal stem cells.
Aniridia may occur as part of another genetic condition known as WAGR syndrome. It affects more than one gene on the 11^th chromosome and the exact mutation can vary between patients. The acronym WAGR describes the four most common symptoms: Wilms’ tumor (kidney cancer affecting children), genitourinary abnormalities, aniridia and mental retardation.
Things to do
When a newborn child is diagnosed with aniridia, there are some actions that need to be taken.
It is impossible to define very specific indications, since in each area of Europe access to healthcare and social assistance are regulated by different national health systems and policies.
Nevertheless, every child with aniridia should at least:
- be offered genetic investigation, to establish if aniridia is isolated or part of the WAGR syndrome and to identify the mutation on PAX6 when possible;
- perform regular ophtalmological checks, at a frequency established according to eye conditions;
- perform regular ultrasound tests of the kidneys, for an early detection of Wilms’ tumor;
- be followed, especially during the first years of life, by therapists specialised in visually impaired children, to help the best possible development of vision and to prevent problems associated with low vision that might affect other developmental areas (movement, speech, learning…).
Source: Aniridia Europe website