Aniridia

One type of genetic test is available to check for deletions and another for mutations. A PAX6 sequence analysis checks for mutations, and deletion testing checks for deletions; as either are possible causes of aniridia, labs tend to perform both simultaneously.

As isolated aniridia inherited from a parent can appear in an affected child's siblings, these siblings warrant a test as well. If a child affected with aniridia has no family history of the disorder, the risk of aniridia for her siblings and other family members is low. If the child is indeed the first in the family with aniridia, she has most likely experienced a random mutation to her PAX6 gene.

Aniridia can be diagnosed using a clinical exam by an ophthalmologist, after which the exact cause may be determined with genetic testing.

Four of the ways aniridia is clinically diagnosed are:

1. High-Frequency Ultrasound Biomicroscopy: used on infants to detect a scarred or swollen cornea which can be a sign of complete or partial absence of the iris
2. Optical Coherence Tomography: a procedure that may be difficult for younger children, but can reveal underdevelopment of certain parts of the eye in atypical cases
3. Slit Lamp Fundoscopy and/or Indirect Ophthalmoscope: a method that can also reveal underdeveloped parts of the eye and other abnormalities associated with the optic disc
4. Slit Lamp Examination: detects iris abnormalities, cataracts, glaucoma, and scarred or vascularized corneas

For a genetic diagnosis, a sample from the patient is sent to a lab for an analysis of the PAX6 gene. This sample is most often blood, but some labs will also accept a saliva sample or a buccal swab.

A prenatal diagnosis of aniridia is possible through one of two methods: a chorionic villi sampling in the first trimester or amniocentesis in the second trimester. Both procedures pose some risk to the pregnancy.

Most healthcare providers will only offer prenatal testing for aniridia if a mutation has already been identified in the family. To learn more about prenatal testing for aniridia see a genetic counselor. Genetic counselors can be found on the National Society of Genetic Counselors website.

Individuals may seek out genetic testing for several reasons. One reason is to confirm that a diagnosis of isolated aniridia really is isolated, rather than the result of a genetic syndrome as Wilms tumor-aniridia-genital anomalies-retardation (WAGR) that has aniridia as one of its features. If the aniridia is indeed part of a different syndrome, the affected individual may need additional screening and management. Another reason to seek testing is for future family planning. Knowing the genetic cause can allow for prenatal testing or even pre-implantation genetic diagnosis. A medical geneticist can be found by asking your doctor for a referral or looking on the American College of Medical Geneticists website. Genetic counselors can be found on the National Society of Genetic Counselors website.

Preimplantation genetic diagnosis is a procedure where an embryo is created in a lab using the biological parents' sperm and egg, and can then be screened for the already identified PAX6 mutation in the family. Once an embryo without a mutation is identified, it can be implanted into the mother and so the baby will not have aniridia. This can only be done if a mutation has already been identified.