Aniridia syndrome is a genetic congenital eye and medical syndrome usually detected at birth. The most noticeable feature is that the baby has dark eyes with no real iris color. Although, "aniridia" means lack of iris, this is the LEAST important issue of "aniridia syndrome". When named many years ago, all physicians noted was the child had no iris, low vision and possible light sensitivity. The important issues are not "what color your child's eyes are", it is maintaining what vision they do have. For this reason, it is important to know about the conditions which make up "aniridia syndrome."
A syndrome is a set of medical issues, all or mostly found in one child or adult that make up a condition. Today, we know much more about the multiple issues, and it is now referred to as "aniridia syndrome". In most cases, these eye and medical issues that make up "aniridia syndrome" can develop anytime from birth into young adulthood. Many of the issues that define "aniridia syndrome" are common in the general population like glaucoma, cataracts, corneal disease, diabetes, autism spectrum disorders and metabolic issues. However, unlike a person in the general population, the child or adult with "aniridia syndrome" lives with many of these issues throughout their life, and they usually occur earlier than those in the general population such as in the case of cataracts and corneal scarring.
Genetics and Statistics
There are 3 types of inheritance - Sporadic, Familial, and Recessive.
Aniridia Syndrome occurs through a genetic mutation. Recessive inheritance is not often found in the USA. More information on this will be in the bullet point below. In general, sporadic cases, it means that neither parent has aniridia syndrome. Once a sporadic case is identified, a familial inheritance pattern (autosomal dominant) will occur from then on. Familial inheritance cases mean that one of the child's parents has aniridia syndrome. In genetics it is known as an autosomal dominant inheritance pattern. This condition is passed down into each successive generation with a 50 percent chance with each pregnancy the man or woman is involved in. Every person with aniridia syndrome will have a 50 percent chance of producing a child with aniridia syndrome with each pregnancy. For this reason, there is a need to help people who are affected visually, help research in this area, and stop the progression in family lines.
Think of a pie...1/3 of that pie is children born with sporadic aniridia syndrome. Neither of their parents have this genetic condition. Then 2/3 of the pie are those who have familial inheritance of aniridia syndrome because one of their parents actually has this genetic syndrome.
Since aniridia syndrome is a genetic disorder, there are other conditions that are sometimes associated with it such as WAGR Syndrome. WAGR is an acrostic for Wilms’ tumor (cancerous tumor of the kidney usually occurring before age 8 years old), Aniridia, Genitourinary abnormalities or Gonadblastoma, and Retardation or learning disabilities. This larger genetic deletion includes the PAX6 gene and the nearby WT1 gene. About one-third of those born with sporadic cases of aniridia will have WAGR Syndrome. Most pediatricians suggest genetic testing if a diagnosis of sporadic aniridia syndrome is found at or shortly after birth. This is because of the possibility of WAGR Syndrome.
Since those with WAGR syndrome do have aniridia syndrome, we welcome them to be a part of Aniridia Foundation International. In addition, the International WAGR Syndrome Association at www.wagr.org is also a very informative and supportive group for those dealing with the extra issues of WAGR syndrome.
According to recent studies, approximate occurrence rate is 1/40,000 births; although, rates differ in various areas of the world. We think it may be more prevalent due to more familial inheritance births as medical care and knowledge of aniridia syndrome become better.
For example: in countries where marriage between first cousins is allowed or encouraged, the recessive inheritance may show aniridia syndrome as more common in these populations such as India, Pakistan, Saudi Arabia.
What causes aniridia syndrome?
There are various genes that may be affected; however, by far the most common is a genetic error on the short arm of the chromosome 11p13 involving the PAX 6 gene. PAX 6 has been known for quite some time as being responsible for the development of the eye; however, now we also know that it plays a part in many parts of the body including development and maintenance of the eyes, pancreas, central nervous system, olfactory system and parts of the brain.
Aniridia syndrome is produced by a failure in development of the ocular globe during pregnancy and because of the underdevelopment of eye structures such as the optic nerve and retina, the infant is born with vision in the ranges of low vision to legal blindness. Actually the underdeveloped iris area is just a thick collar of tissue around the outer edge that never developed. The muscles which open and close the pupil are missing entirely.
The underdevelopment of eye structures involves malformation of the retina, amblyopia, foveal hypoplasia, nystagmus, lens sublaxation (dislocation), and macula and optic nerve disease. Since genetic errors vary, so do the visual acuities of those with aniridia syndrome. On average, most have vision of legal blindness (20/200) or worse; however, some do have "low vision" (20/40 to under 20/200).
Yes, lack of an iris may cause light sensitivity; however, the real problems are the conditions which "make up" this syndrome and that can cause loss of the remaining vision.
The issues that make up aniridia syndrome that can cause further vision loss anytime from birth during their life are: glaucoma, retinal detachments, corneal degeneration (scarring), cataracts, Aniridia Fibrosis Syndrome (AFS), macula and optic nerve disease.
Medical conditions such as glucose intolerance to insulin resistance, diabetes, auditory processing issues, autism spectrum disorders, and weight issues have been associated. The Aniridia Foundation International research program is looking into these issues, as well as, other areas which need further studies.
Important Notes to Keep in Mind
While aniridia syndrome has its challenges with each of the multiple eye and medical conditions, here are a couple important notes about the ones that can cause more loss of vision or life. To read more about these and the other issues in aniridia syndrome, please go to our Booster area for more detailed information on latest research, treatments or experiences.
Glaucoma: Glaucoma is called the "thief of sight" because there may not be any signs before much damage is done. Since glaucoma in people with aniridia can develop at any age including birth, it is important to have the child’s pressure checked at birth and every 6 months thereafter.
Wilms' Tumor: Due to some rare unusual findings of normal genetic karotype patients later producing a Wilms’ tumor, we suggest that all children up to eight years old with sporadic aniridia have ultrasounds every 3 months to monitor their kidneys. While the risk is lower with a genetic test in which the WT1 gene is intact, this ultrasound monitoring is simple, non-invasive, and is a good preventive measure. Most Wilms’ tumors, if caught early, can be cured.
Corneal Scarring (Degeneration): People with aniridia syndrome usually develop corneal scarring at some point in their life. Most are seen in their teens and 20’s. However, it can develop earlier, especially if there is a trauma to the corneal surface such as a scratch or an abrasion from a contact lens. This is why our expert ophthalmologists do not suggest contact lenses, especially for infants and young children as it may bring on the corneal scarring sooner.
It has been estimated that about 90 percent of those with aniridia syndrome develop the corneal scarring. The cornea is the outer layer of the eye in front of the iris and pupil. The reason for this scarring is now being investigated further. Over a decade ago, the hypothesis was due to the eye’s limbal stem cells either being underdeveloped or not working properly to generate new corneal tissue. This sounded logical as these limbal stem cells are located in the area where the underdeveloped "non working" iris is located. However, new research is now also adding that perhaps the cornea cells themselves are different in aniridia syndrome patients and not working properly either. This is an important aspect to research as it may mean that correcting the limbal stem cell deficiency will not be the only issue needed.
This also brings into favor other treatments for the corneal scarring such as the artificial cornea (Boston Keratoprothesis) which does not require the toxic immunosuppressive medications needed to keep a limbal stem cell transplant from rejecting. We are learning now from the limbal stem cell transplants done a decade or more ago. Limbal stem cell transplants for some by genetically matched family members have been done to address some of the things the medical community has learned over the past decade, yet we do not have long term results for this new approach.
Limbal stem cells are responsible for making new cornea cells to keep the corneal surface healthy and clear. However, the limbal stem cells and cornea cells in a person with aniridia do not work properly. When their cornea cells are sloughed off, the cells from the white part of the eye (sclera) grow in to cover the area. This Condition is called Limbal Stem Cell Deficiency (LSCD). The cells from the scleral area are not transparent like the cornea cells. This is what reduces the vision of the person with aniridia.
Limbal stem cell deficiency can be found early by a corneal specialist experienced in aniridia syndrome. As it occurs, reading becomes difficult, then larger objects or people are difficult to see. As the condition worsens, the person will only see light and dark contrasts. The good news is that LSCD can be treated depending on which treatment path you choose. For more detailed information and personal experiences go to our private forum. We suggest to all our families to have their children, usually around age 11, monitored so that LSCD can be treated when it is necessary by an experienced corneal surgeon who is knowledgeable about aniridia syndrome. It is also important to note that corneal transplants are not successful for those with aniridia syndrome and should not be done.