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Heterozygous mutations of OTX2 cause severe ocular malformations
Nicola K Ragge1, Alison G Brown, Charlotte M Poloschek
1Department of Adnexal Surgery, Moorfields Eye Hospital, London, United Kingdom.
American Journal of Human Genetics
|April 23, 2005
Summary
Mutations in the OTX2 gene cause major human eye malformations like anophthalmia. These OTX2 gene mutations can be inherited or arise anew, impacting genetic counseling due to mosaicism and reduced penetrance.
Area of Science:
- Genetics
- Developmental Biology
- Ophthalmology
Background:
- Major human eye malformations (microphthalmia, anophthalmia) often lack clear Mendelian inheritance.
- Genetic mapping is frequently infeasible for these complex phenotypes.
Purpose of the Study:
- To identify genetic causes of familial ocular malformations.
- To investigate the role of the OTX2 gene in eye development and malformations.
Main Methods:
- Candidate-gene approach focusing on the OTX2 homeobox gene.
- Analysis of coding-region changes in affected families.
- Correlation of OTX2 expression patterns with observed phenotypes.
- Magnetic resonance imaging (MRI) for detecting structural brain and optic nerve defects.
Main Results:
- Heterozygous coding-region mutations in OTX2 were identified in eight families with ocular malformations.
- OTX2 expression patterns in human embryos correlate with observed eye phenotypes, ranging from anophthalmia to retinal defects.
- MRI revealed associated defects in the optic nerve, optic chiasm, and brain.
- Four families showed simple inheritance of OTX2 loss-of-function mutations, with evidence of de novo events and gonosomal mosaicism.
- Four families exhibited complex inheritance patterns, suggesting OTX2 mutations alone do not always determine phenotype.
Conclusions:
- Heterozygous loss-of-function mutations in OTX2 are a significant cause of major human eye malformations.
- High incidence of mosaicism and reduced penetrance associated with OTX2 mutations complicate inheritance patterns and have implications for genetic counseling.