An international team of researchers have identified a gene that, when mutated, causes Duane syndrome, a common disorder that restricts the movement of the eyes.

The research team, including scientists from the United Kingdom and the United States, published its article on Thursday in Science Express.

Duane syndrome is a congenital eye movement disorder that causes eye muscles to contract and relax when they should not. It develops in the womb where it affects nerve growth in the eye. Sufferers of the syndrome have limited eye movement sideways towards the ear or nose.

To isolate the Duane syndrome gene, the research team studies DNA extracted from blood or saliva samples provided by multiple members of different families. Finally, they identified a unique mutation in the gene CHN1 in each of the seven families. This gene encodes a signaling molecule, which previous studies in mice had shown to be essential for normal upper motor neuron axon guidance.

Then, they introduced the mutation into chick embryos (which have a visual system very similar to that of humans) and produced similar defects in nerve growth.

Their new results confirms and expands the long-standing hypothesis that many congenital complex eye movement disorders arise from improper development of the nerves that control movement of the eyeball. Researchers once thought the disorders resulted from muscle defects.

Duane syndrome usually causes vision problems. Most sufferers of the condition are diagnosed by the age of 10. It is more prevalent in women and in the left eye. It is believed to affect around half a million people worldwide.

"By understanding how this gene causes Duane syndrome, we can begin to achieve a wider understanding of how the visual system develops in the womb. This raises the possibility of better diagnosis and even genetic treatments for visual conditions such as Duane syndrome," said John Chilton, a British researcher from Peninsula Medical School.

(Xinhua News Agency July 25,2008)