Microphthalmia

Microphthalmia
Unilateral Microphthalmia
Classification and external resources
Specialty	medical genetics
ICD-10	Q11.2
ICD-9-CM	743.1
DiseasesDB	29618
eMedicine	oph/572
GeneReviews	Anophthalmia / Microphthalmia Overview

Microphthalmia (Greek: μικρός micros = small; ὀφθαλμός ophthalmos = eye), also referred as microphthalmos, is a developmental disorder of the eye in which one (unilateral microphthalmia) or both (bilateral microphthalmia) eyes are abnormally small and have anatomic malformations. Different from nanophthalmos in which the eye is small in size but has no anatomical alterations. ^[1]

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

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 may be autosomal dominant, autosomal recessive or X linked. The following genes have been implicated in microphthamia, many of which are transcription and regulatory factors:

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 eyeball) 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.

See also

• Abdominal Musculature Absent With Microphthalmia And Joint Laxity

References

External links

• GeneReviews/NCBI/NIH/UW entry on Anophthalmia / Microphthalmia Overview
• Parent Support group for parents with Anophthalmic and Microphthalmic children MAPS
• Anophthalmia and Microphthalmia Resource Guide from the National Eye Institute (NEI).
• GeneReviews/NCBI/NIH/UW entry on Microphthalmia with Linear Skin Defects Syndrome
• MACS The Micro and Anophthalmic Children's Society - Offers support and Information to families in the UK and around the world
• Ensembl
• HUGO Gene Nomenclature Committee
• OMIM-Online Mendelian Inheritance in Man