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Duane syndrome is an inherited complex eye movement disorder affecting one in 1,000 people, rendering them unable to move one or both eyes outward. Contradicting the accepted belief that this is due to muscle defects, researchers at Children's, led by
neurologist Elizabeth Engle, MD, senior associate in Neurology, have identified a gene mutation in Duane syndrome that results in improper development of the nerves controlling eyeball movement.
According to Dr. Engle, a popular but unproven hypothesis says that human disorders could arise from growing nerve fibers incapable of migrating to the right location, due to errors in axon guidance. She and her team identified a unique mutation in the gene CHN1, which results in an overactive signaling molecule, a2-chimaerin. This, in turn, disconnects the response of lower motor neurons to growth signals, so they aren't appropriately targeted to the relevant eye muscles.
Dr. Engle describes her findings, published in the August 8 issue of Science, as "a nice example of an error in the development of a very simple motor circuit." And since vision requires precise, coordinated eye movements, congenital disorders like Duane syndrome are a sensitive indicator of such errors, she adds. By first understanding the wiring of such simple circuits, she hopes to eventually gain insight into neural circuits of a more complex order.
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