by Katerina Maher

Created on: March 05, 2009   Last Updated: March 10, 2009

What is Aniridia? It is a rare condition of the eye where there is the absence of the iris. It is what one would define as a congenital defect, one is born with this condition. You cannot develop it later in life. In the US, 1/90,000 people will be born with it. As relieving as this news is, one cannot simply lose one's iris, it still does not answer the question as to how one can get Aniridia.

There are two categories of how one can get Aniridia: 1) genetic causes; 2) sporadic cases. Nothing can be done to explain the sporadic cases. Essentially, no one in the family has ever had it and there is no obvious reason why they might have been born without an iris. Theory would suggest that there was a sporadic mutation in the foetuses genes, of the parents' sperm or ovum, (egg), which led to Aniridia. Sometimes sporadic Aniridia affects a specific area on a chromosome 11, known as the AN2 aniridia region, called the WT1 region. The affected chromosome unfortunately can also lead to other problems in the body, causing a kidney cancer known as a "Wilm's tumour" or a nephroblastoma. Luckily, this tumour is quite manageable. Affected individuals of sporadic Aniridia can also have other problems with their urination and the anatomy in that area as well as mental retardation.

Genetic causes are familial, as they are caused by genes that were passed on by one's parents. There are two genetic causes. The first is autosomal recessive, meaning that both parents are carriers of a certain gene. Both parents have one of this mutated gene, but since everyone has two copies of each gene, the parents were unaffected. Unfortunately, if an affected child is born, they will have two of the mutated genes and no spare normal one. Thus, they will develop Aniridia, however this form is very rare.

The other genetic variation is autosomal dominant, which means one only needs a single mutated gene to develop this condition. Usually, the parents will be affected as well. The autosomal dominant variant also is affected in the AN2 region, however it is the PAX6 region that is affected. The good news is that if Anirida runs in the family, one need not worry about the risk of a Wilm's tumour.

Therefore, if you have been lucky enough to be born with a perfectly functioning iris, don't worry, you will not lose it. One has to be born with Aniridia. As for the reasons why one is born with it, it can either be genetic or sporadic. Despite the different causes, Aniridia is still a very rare condition.

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