ABCB6

Coloboma, Isolated

Clinical Characteristics
Ocular Features: 

Colobomas of the uveal tract are often found in association with other ocular anomalies including those with systemic disease. They are usually located in the inferonasal quadrant as a result of defective closure of the embryonic fissure in the optic cup.  Most involve the nearly complete iris and resemble a keyhole but they may also be partial resulting in an oval pupil.  They are sometimes unilateral in which case the involved iris may be more heavily pigmented than the contralateral one.  They may involve only the iris (simple coloboma) but often are more extensive with involvement of the ciliary body, retina, lens, choroid, and even the optic nerve.  They are frequently associated with microphthalmia (or microphthalmia with cyst [5.6%]) and microcornea (79%). 

Systemic Features: 

None by definition.

Genetics

Isolated colobomas are clinically and genetically heterogeneous resulting from mutations in SHH (7q36.3), PAX6 (11p13), and ABCB6 (2q35) among others.  Large pedigrees with typical autosomal dominant transmission patterns have been reported.

Homozygous mutations in SALL2 (14q11.1-q12.1) have also been reported in patients with isolated colobomas.  Studies of sall2-deficient mice show defects in closure of the anterior optic fissure while posterior closure proceeds normally.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Simple iris colobomas usually do not require treatment.  The visual prognosis depends upon the structures involved.  Those with microcornea usually have a lower acuity and, of course, eyes with the most extensive involvement of the uveal tract and/or the optic nerve may have the least vision. Low vision aids can be helpful in selected individuals.

References
Article Title: 

Mutation of SALL2 causes recessive ocular coloboma in humans and mice

Kelberman D, Islam L, Lakowski J, Bacchelli C, Chanudet E, Lescai F, Patel A, Stupka E, Buck A, Wolf S, Beales PL, Jacques TS, Bitner-Glindzicz M, Liasis A, Lehmann OJ, Kohlhase J, Nischal KK, Sowden JC. Mutation of SALL2 causes recessive ocular coloboma in humans and mice. Hum Mol Genet. 2014 Jan 12. [Epub ahead of print].

PubMed ID: 
24412933

ABCB6 Mutations Cause Ocular Coloboma

Wang L, He F, Bu J, Liu X, Du W, Dong J, Cooney JD, Dubey SK, Shi Y, Gong B, Li J, McBride PF, Jia Y, Lu F, Soltis KA, Lin Y, Namburi P, Liang C, Sundaresan P, Paw BH, Li DY, Phillips JD, Yang Z. ABCB6 Mutations Cause Ocular Coloboma. Am J Hum Genet. 2012 Jan 13;90(1):40-8.

PubMed ID: 
22226084
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