Microphthalmia

Microphthalmia
Classification and external resources

Unilateral Microphthalmia
ICD-10 Q11.2
ICD-9 743.1
DiseasesDB 29618
eMedicine oph/572
GeneReviews Anophthalmia / Microphthalmia Overview

Microphthalmia also referred to as microphthalmos, nanophthalmia or nanophthalmos, is a developmental disorder of the eye that literally means small eye (micros = small; ophthalmos = eye). One (Unilateral Microphthalmia) or both (Bilateral Microphthalmia) eyes may be involved [1]

Contents

Presentation

The presence of a small eye within the orbit can be a normal incidental finding but in most cases it is abnormal and results in blindness. The incidence is 14 per 100,000 and the condition affects 3-11% of blind children.

Causes

The major causes for this disorder are genetic but environmental factors have also been implicated such as exposure to radiation, chemicals, or viruses. Microphthalmia in newborns is sometimes associated with fetal alcohol syndrome[1] or infections during pregnancy, particularly herpes simplex virus, rubella and cytomegalovirus (CMV), but the evidence is inconclusive. Genetic causes of microphthalmia include chromosomal abnormalities (trisomy 13 (Patau syndrome), Triploid Syndrome, and Wolf-Hirschhorn Syndrome) or monogenetic Mendelian disorders. The latter maybe autosomal dominant, autosomal recessive or X linked. Genes that have been implicated in microphthamia include many transcription and regulatory factors. Those identified from family studies include the following:

HGNC symbol Description OMIM Type
BCOR BCL6 corepressor 300166 MCOPS2
CRYBA4 crystallin, beta A4
FOXE3 forkhead box E3
GDF6 growth differentiation factor 6
MITF microphthalmia-associated transcription factor
OTX2 orthodenticle homeobox 2
PAX6 paired box 6
PITX3 Paired-like homeodomain transcription factor 3
RAX retina and anterior neural fold homeobox
SHH sonic hedgehog homolog
SIX6 SIX homeobox 6
SOX2 SRY (sex determining region Y)-box 2 206900 MCOPS3
VSX1 visual system homeobox 1
VSX2 (CHX10) visual system homeobox 2

How these genes result in the eye disorder is unknown but it has been postulated that interference with the process of eye growth after birth may be involved in contrast to anophthalmia (absence of eye ball) which originates much earlier during foetal development. SOX2 has been implicated in a substantial number (10-15%) of cases and in many other cases failure to develop the ocular lens often results in microphthamia. Microphthalmia-associated transcription factor (MITF) located on chromosome 14q32 is associated with one form of isolated microphthalmia (MCOP1. In mammals the failure of expression of the transcription factor, MITF (microphthalmia-associated transcription factor), in the pigmented retina prevents this structure from fully differentiating. This in turn causes a malformation of the choroid fissure of the eye, resulting in the drainage of vitreous humor fluid. Without this fluid, the eye fails to enlarge, thus the name microphthalmia.The gene encoding the microphthalmia-associated transcription factor (MITF) is a member of the basic helix-loop-helix-leucine zipper (bHLH-ZIP) family. Waardenburg syndrome type 2 (WS type 2) in humans is also a type of microphthalmia syndrome. Mutations in MITF gene are thought to be responsible for this syndrome. The human MITF gene is homologous to the mouse MITF gene (aka mouse mi or microphthalmia gene); mouse with mutations in this gene are hypopigmented in their fur. The identification of the genetics of WS type 2 owes a lot to observations of phenotypes of MITF mutant mice.

References

See also

  • Abdominal Musculature Absent With Microphthalmia And Joint Laxity

External links



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Look at other dictionaries:

  • Microphthalmia — Mi croph*thal mi*a, Microphthalmy Mi croph*thal my, n. [Micro + Gr. ofqalmo s eye.] An unnatural smallness of the eyes, occurring as the result of disease or of imperfect development. [1913 Webster] …   The Collaborative International Dictionary of English

  • Microphthalmia — An abnormally small eye, a congenital malformation (birth defect) of the globe. The related term anophthalmia means no eye and refers to absence of the globe and ocular tissue from the orbit. Microphthalmia may involve one or both eyes. It may… …   Medical dictionary

  • Microphthalmia — mažaakystė statusas T sritis gyvūnų raida, augimas, ontogenezė, embriologija atitikmenys: lot. Microphthalmia ryšiai: platesnis terminas – akies trūkumas …   Veterinarinės anatomijos, histologijos ir embriologijos terminai

  • Microphthalmia — mažaakystė statusas T sritis embriologija atitikmenys: lot. Microphthalmia ryšiai: platesnis terminas – akies trūkumai …   Medicininės histologijos ir embriologijos vardynas

  • microphthalmia — mi·croph·thal·mia …   English syllables

  • microphthalmia — ˌmīˌkräfˈthalmēə, ÷ kräp|th noun ( s) Etymology: New Latin, from micr + ophthalmia : abnormal smallness of the eye usually occurring as a congenital anomaly …   Useful english dictionary

  • Microphthalmia-associated transcription factor — Identifiers Symbols MITF; MI; WS2; WS2A; bHLHe32 External IDs …   Wikipedia

  • Microphthalmia–dermal aplasia–sclerocornea syndrome — Classification and external resources OMIM 309801 Microphthalmia–dermal aplasia–sclerocornea syndrome (also known as MIDAS syndrome [1]) is a condition characterized by linear skin lesions …   Wikipedia

  • Microphthalmia-associated transcription factor — Le facteur de transcription associé à la microphtalmie (en anglais, Microphtalmia associated Transcription Factor abrégé en MITF) est un facteur de transcription en hélice boucle hélice impliqué dans le développement mélanocytaire et la survie de …   Wikipédia en Français

  • MITF — Microphthalmia associated transcription factor Le facteur de transcription associé à la microphtalmie (en anglais, Microphtalmia associated Transcription Factor abrégé en MITF) est un facteur de transcription en hélice boucle hélice impliqué dans …   Wikipédia en Français


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