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Babies born with no eyes: scientists identify gene responsible

UCD researchers have identified the underlying gene responsible for three major eye defects that cause malformed or missing eyes in children from birth. These new findings will inform optimal patient management and counselling of affected families as well as providing detail on the biological processes within eye development. The findings of this project funded by the National Children’s Research Centre and the Health Research Board are published in the current issue (December 2011) of the journal, Human Mutation.

Anophthalmia (absence of one or both eyes), microphthalmia (small eye) and coloboma (malformed eye) arise during embryonic development. Although individually rare, these three major structural eye defects account for 11% of visual impairments. They can also be associated with other birth defects such as malformations of the heart, lungs and diaphragm.

Led by Dr Sean Ennis, UCD School of Medicine & Medical Science and in conjunction with UCD Conway clinicial associate fellow, Professor Andrew Green from the National Centre for Medical Genetics, this study involved nine members of a large Irish family of nomadic descent who suffer with one or more of the three eye defects to varying degrees of severity.

Using advanced gene sequencing technologies, researchers firstly scanned for regions of DNA shared by all patients before analysing a single common region for the disease gene. They pinpointed STRA6, a gene responsible for transporting vitamin A into cells.

In collaboration with Dr Hui Sun and Dr Riki Kawaguchi in the University of California, the research team went on to show that the genetic mutation identified in these patients significantly impairs the ability of STRA6 to transport vitamin A into the cells. Consequently, the amount of vitamin A needed to support normal eye development in the embryo is lacking.    

Dr Breandan Kennedy in UCD Conway Institute and the School of Biomolecular & Biomedical Science developed a zebrafish model of the disease in an effort to confirm the importance of vitamin A in the process of eye development. He and postdoctoral researcher, Dr Maria Morrissey reproduced the patients’ clinical symptoms using a pharmacological drug to reduce vitamin A levels within the cell.
Not only has this project led to very significant advances in the understanding of individual genes that can cause microphthalmia, anophthalmia and coloboma, it also adds important diagnostic criteria to the field of eye malformations.

IRCSET-funded doctoral candidate, Jillian Casey who is first author on this publication explains, ‘Changes in the DNA sequence of STRA6 have previously been shown to give rise to Matthew-Wood syndrome, a severe developmental disorder that includes eye malformations. Currently, only patients with Matthew-Wood Syndrome are considered for STRA6 genetic testing. Our findings show that STRA6 mutations can also give rise to isolated eye malformations and suggest that patients with eye defects of unknown cause should also be considered for STRA6 testing’.

Commenting on the significance of the research, Dr Sean Ennis says, ‘Having identified the novel genetic basis of these eye defects in the Irish population, we now want to translate this research into clinical practice. This will involve developing and introducing a genetic test to the diagnostic laboratory at the National Centre for Medical Genetics (NCMG).

The molecular laboratory at NCMG offer carrier testing for genetic disorders common in the population and this condition can now be added to the testing panel. Accurate carrier testing and genetic counselling can be offered to those planning pregnancies. Ultimately, this work may be used to develop preventive measures or possible treatments in the future’.

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