Microphthalmia, isolated with coloboma 3 is a rare inherited disorder characterized by small eyes (one or both) and eye colobomas. The clinical findings are confined to the eye in this condition. The globe is abnormally small (defined by some as less than 20 mm in length in at least one eye). Incomplete penetrance and variable expression are typical but often the cornea is small and may be cloudy with anterior synechia suggesting that anterior chamber dysgenesis may also be a feature in some cases. Visual acuity depends on the structures involved. It is not uncommon for other ocular abnormalities to occur in association with the malformed globes, such as cataracts, microcornea, sclerocornea and optic nerve dysplasia.
MCOPCB3 is caused by mutations in the CHX10 gene on chromosome 14q24.3. CHX10 plays a significant role in the specification and morphogenesis of the sensory retina. It may also participate in the development of the cells of the inner nuclear layer, particularly bipolar cells.
In affected members of a consanguineous Jewish Syrian family from Aleppo with microphthalmia/clinical anophthalmia and colobomas of the iris, Bar-Yosef et al. (2004) identified homozygosity for a splice site mutation (IVS1-1G>A) in the CHX10 gene.
Percin et al. (2000) examined a 2-month-old male infant, born of clinically normal consanguineous parents from the United Arab Emirates, he had bilateral microphthalmia with no pupillary aperture, a funnel-shaped retinal detachment inserted into the optic disc on the right, and a lesion compatible with a dislocated lens with surrounding membrane formation or localized retinal detachment on the left. In addition to the ocular anomalies, the child had undescended testes. At molecular level, this patient was found to be homozygous for missense mutation (599G>C; R200P) in the CHX10 gene.