Aniridia

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Aniridia
Aniridia.jpg
A man with aniridia
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Aniridia is the absence of the iris, a muscular structure that opens and closes the pupil to allow light into the eye. It is also responsible for eye color. Without it, the central eye appears all black. It can be congenital, in which both eyes are usually involved, or caused by a penetrant injury. [1] Isolated aniridia is a congenital disorder that is not limited to a defect in iris development, but is a panocular condition with macular and optic nerve hypoplasia, cataract, and corneal changes. [2] Vision may be severely compromised and the disorder is frequently associated with some ocular complications: nystagmus, amblyopia, buphthalmos, and cataract. [1] 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).

Contents

PAX6

Phenotypic expression of aniridia with PAX6 gene mutation. The aniridic probands showed typical features of sclerocornea with nystagmus in proband 28-1 (A); Foveal hypoplasia in proband 27-1 (B); Ptosis, microcornea with dislocated cataractous lens in proband 10-1 (C); Ectopia lentis in proband 16-1 (D). Human eyeball with phenotypic expression of aniridia with PAX6 gene mutation.jpg
Phenotypic expression of aniridia with PAX6 gene mutation. The aniridic probands showed typical features of sclerocornea with nystagmus in proband 28–1 (A); Foveal hypoplasia in proband 27–1 (B); Ptosis, microcornea with dislocated cataractous lens in proband 10–1 (C); Ectopia lentis in proband 16–1 (D).

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). [3] 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.

Defects in the PAX6 gene cause aniridia-like ocular defects in mice (as well as Drosophila ). Aniridia is a heterozygous disorder, meaning that only one of the two chromosome 11 copies is affected. 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 sustain severe brain damage. [4]

Types

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. Sporadic aniridia mutations may affect the WT1 region adjacent to the AN2 aniridia region, causing a kidney cancer called nephroblastoma (Wilms tumor). These patients often also have genitourinary abnormalities and intellectual disability (WAGR syndrome).

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. Thus, some aniridic individuals are only missing a relatively small amount of iris, do not have foveal hypoplasia, and retain relatively normal vision. Presumably, the genetic defect in these individuals causes less "heterozygous insufficiency," meaning they retain enough gene function to yield a milder phenotype.

Mutational analysis

Molecular (DNA) testing for PAX6 gene mutations (by sequencing of the entire coding region and deletion/duplication analysis) is available for isolated aniridia and the 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. [5]

Symptoms

Aniridia can cause many symptoms, such as:

Treatment

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. [7]

See also

Related Research Articles

<span class="mw-page-title-main">Albinism in humans</span> Condition characterized by partial or complete absence of pigment in the skin, hair and eyes

Albinism is a congenital condition characterized in humans by the partial or complete absence of pigment in the skin, hair and eyes. Albinism is associated with a number of vision defects, such as photophobia, nystagmus, and amblyopia. Lack of skin pigmentation makes for more susceptibility to sunburn and skin cancers. In rare cases such as Chédiak–Higashi syndrome, albinism may be associated with deficiencies in the transportation of melanin granules. This also affects essential granules present in immune cells, leading to increased susceptibility to infection.

<span class="mw-page-title-main">Tietz syndrome</span> Congenital disorder

Tietz syndrome, also called Tietz albinism-deafness syndrome or albinism and deafness of Tietz, is an autosomal dominant congenital disorder characterized by deafness and leucism. It is caused by a mutation in the microphthalmia-associated transcription factor (MITF) gene. Tietz syndrome was first described in 1963 by Walter Tietz (1927–2003) a German Physician working in California.

<span class="mw-page-title-main">X-linked recessive inheritance</span> Mode of inheritance

X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males and in females who are homozygous for the gene mutation, see zygosity. Females with one copy of the mutated gene are carriers.

<span class="mw-page-title-main">Coloboma</span> Hole in one of the structures of the eye

A coloboma is a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc. The hole is present from birth and can be caused when a gap called the choroid fissure, which is present during early stages of prenatal development, fails to close up completely before a child is born. Ocular coloboma is relatively uncommon, affecting less than one in every 10,000 births.

Microphthalmia, also referred as microphthalmos, is a developmental disorder of the eye in which one or both eyes are abnormally small and have anatomic malformations. Microphthalmia is a distinct condition from anophthalmia and nanophthalmia. Although sometimes referred to as 'simple microphthalmia', nanophthalmia is a condition in which the size of the eye is small but no anatomical alterations are present.

<span class="mw-page-title-main">Mulibrey nanism</span> Medical condition

Mulibrey nanism is a rare autosomal recessive congenital disorder. It causes severe growth failure along with abnormalities of the heart, muscle, liver, brain and eye. TRIM37 is responsible for various cellular functions including developmental patterning.

WAGR syndrome is a rare genetic syndrome in which affected children are predisposed to develop Wilms' tumour, aniridia, genitourinary anomalies, and mental retardation. The "G" is sometimes instead given as "gonadoblastoma", since the genitourinary anomalies can include tumours of the gonads.

<span class="mw-page-title-main">PAX6</span> Protein-coding gene in humans

Paired box protein Pax-6, also known as aniridia type II protein (AN2) or oculorhombin, is a protein that in humans is encoded by the PAX6 gene.

Denys–Drash syndrome (DDS) or Drash syndrome is a rare disorder or syndrome characterized by gonadal dysgenesis, nephropathy, and Wilms' tumor.

<span class="mw-page-title-main">Kaufman oculocerebrofacial syndrome</span> Medical condition

Kaufman oculocerebrofacial syndrome, also known as blepharophimosis-ptosis-intellectual disability syndrome, is an extremely rare autosomal recessive congenital disorder characterized by severe mental retardation, brachycephaly, upslanting palpebral fissures, eye abnormalities, and highly arched palate. It was characterized in 1971; eight cases had been identified as of 1995. To date, the amount of cases is disputed, with sources claiming the number ranges from 14 to 31.

<span class="mw-page-title-main">Papillorenal syndrome</span> Medical condition

Papillorenal syndrome is an autosomal dominant genetic disorder marked by underdevelopment (hypoplasia) of the kidney and colobomas of the optic nerve.

<span class="mw-page-title-main">Macular hypoplasia</span> Medical condition

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Zonular cataract and nystagmus, also referred as nystagmus with congenital zonular cataract, is a rare congenital disease associated with Nystagmus and zonular cataract of the eye.

<span class="mw-page-title-main">Wilms tumor protein</span> Transcription factor gene involved in the urogenital system

Wilms tumor protein (WT33) is a protein that in humans is encoded by the WT1 gene on chromosome 11p.

Frasier syndrome is a urogenital anomaly associated with the WT1 gene.

<span class="mw-page-title-main">Gillespie syndrome</span> Medical condition

Gillespie syndrome, also called aniridia, cerebellar ataxia and mental deficiency, is a rare genetic disorder. The disorder is characterized by partial aniridia, ataxia, and, in most cases, intellectual disability. It is heterogeneous, inherited in either an autosomal dominant or autosomal recessive manner. Gillespie syndrome was first described by American ophthalmologist Fredrick Gillespie in 1965.

<span class="mw-page-title-main">FOXE3</span> Protein-coding gene in the species Homo sapiens

Forkhead box protein E3 (FOXE3) also known as forkhead-related transcription factor 8 (FREAC-8) is a protein that in humans is encoded by the FOXE3 gene located on the short arm of chromosome 1.

<span class="mw-page-title-main">Cataract-microcornea syndrome</span> Medical condition

Cataract-microcornea syndrome is a rare genetic syndrome characterized by congenital cataracts and microcornea in the absence of any other systemic anomaly or dysmorphism. Clinical findings include a reduction in corneal diameter in both meridians in an otherwise normal eye, as well as an inherited cataract, that is primarily bilateral posterior polar with opacification within the lens periphery which advances to form a total cataract after visual maturity is achieved. Other ocular manifestations, such as myopia, iris coloboma, sclerocornea, and Peters anomaly, may be observed.

Fryns-Aftimos syndrome is a rare chromosomal condition and is associated with pachygyria, severe mental retardation, epilepsy and characteristic facial features. This syndrome is a malformation syndrome, characterized by numerous facial dysmorphias not limited to hypertelorism, iris or retinal coloboma, cleft lip, and congenital heart defects. This syndrome has been seen in 30 unrelated people. Characterized by a de novo mutation located on chromosome 7p22, there is typically no family history prior to onset. The severity of the disorder can be determined by the size of the deletion on 7p22, enveloping the ACTB gene and surrounding genes, which is consistent with a contiguous gene deletion syndrome. Confirming a diagnosis of Fryns-Aftimos syndrome typically consists of serial single-gene testing or multigene panel of genes of interest or exome sequencing.

Meacham syndrome is a rare genetic disorder which is characterized by lung, diaphragmatic and genitourinary anomalies.

References

  1. 1 2 Lang, Gerhard K.; Gareis, O. (2007). Ophthalmology: a pocket textbook atlas (2nd ed.). Stuttgart ; New York: Thieme. p. 208. ISBN   978-1-58890-555-0.
  2. Singh, Daljit; Arun Verma (17 January 2008). "Aniridia". eMedicine. Retrieved 2 February 2010.
  3. Lee, Helena; Khan, Rizwana; O’Keefe, Michael (November 2008). "Aniridia: current pathology and management". Acta Ophthalmologica. 86 (7): 708–715. doi: 10.1111/j.1755-3768.2008.01427.x . PMID   18937825. S2CID   2476524.
  4. Gehring, W. J. (2001). "The genetic control of eye development and its implications for the evolution of various eye-types". Zoology. 104 (3–4): 171–181. doi:10.1078/0944-2006-00022. PMID   16351831.
  5. Neethirajan, Guruswamy; Solomon, Abraham; Krishnadas, Subbaiah Ramasamy; Vijayalakshmi, Perumalsamy; Sundaresan, Periasamy (May 2009). "Genotype/phenotype association in Indian congenital aniridia". The Indian Journal of Pediatrics. 76 (5): 513–517. doi:10.1007/s12098-009-0075-4. PMID   19390808. S2CID   29062682.
  6. "Articles". Cedars-Sinai. Archived from the original on 2020-05-30. Retrieved 2022-02-10.
  7. "FDA OKs First Artificial Iris for Aniridia, Other Iris Defects". Medscape.