|Specialty||Medical genetics Q548719?uselang=en#P1995|
Aniridia is the absence of the iris, usually involving both eyes.
It can be congenital or caused by a penetrant injury.
Aniridia in some individuals occurs as part of a syndrome, such as WAGR syndrome (kidney nephroblastoma (Wilms tumour), genitourinary anomalies and intellectual disability), or Gillespie syndrome (cerebellar ataxia).
The AN2 region of the short arm of chromosome 11 (11p13) includes the PAX6 gene (named for its PAired boX status), whose gene product helps regulate a cascade of other genetic processes involved in the development of the eye (as well as other non-ocular structures).
This PAX6 gene is around 95% similar to the pax gene found in zebrafish, a creature whose ancestors diverged from human evolutionary development around 400 million years ago.
Thus the PAX6 gene is highly conserved across evolutionary lineages.
When both copies are altered (homozygous condition), the result is a uniformly fatal condition with near complete failure of entire eye formation.
In 2001, two cases of homozygous aniridia patients were reported; the fetuses died prior to birth and had severe brain damage.
In mice, homozygous small eye defect (mouse Pax-6) leads to loss of the eyes and nose and the murine fetuses suffer severe brain damage.
Aniridia may be broadly divided into hereditary and sporadic forms.
Hereditary aniridia is usually transmitted in an autosomal dominant manner (each offspring has a 50% chance of being affected), although rare autosomal recessive forms (such as Gillespie syndrome) have also been reported.
Several different mutations may affect the PAX6 gene.
Some mutations appear to inhibit gene function more than others, with subsequent variability in the severity of the disease.
Presumably, the genetic defect in these individuals causes less "heterozygous insufficiency," meaning they retain enough gene function to yield a milder phenotype.
- Online Mendelian Inheritance in Man (OMIM): AN
- Online Mendelian Inheritance in Man (OMIM): Aniridia and absent patella
- Online Mendelian Inheritance in Man (OMIM): Aniridia, microcornea, and spontaneously reabsorbed cataract
- Online Mendelian Inheritance in Man (OMIM): Aniridia, cerebellar ataxia, and mental deficiency (Gillespie syndrome)
For the WAGR syndrome, high-resolution cytogenetic analysis and fluorescence in situ hybridization (FISH) can be utilized to identify deletions within chromosome band 11p13, where both the PAX6 and WT1 genes are located.
In May 2018, the U.S. Food and Drug Administration approved the CustomFlex Artificial Iris, the first synthetic iris for use in adults and children with congenital aniridia or iris defects related to other conditions, such as albinism, traumatic injury, or surgical removal due to ocular melanoma.
The artificial iris is a surgically implanted device made of thin, foldable, medical-grade silicone and is custom-sized and colored for each individual patient.
The prosthetic iris is held in place by the anatomical structures of the eye or, if needed, by sutures.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Aniridia.