Research identifies mechanism responsible for eye movement disorder

Discovery could lead to therapies for this condition, and a better understanding of how genetic mutations in the nervous system cause movement disorders in other parts of the body with a long term view to encouraging the re-growth of damaged cells

A research team from King's College London and the University of Exeter Medical School has identified how a genetic mutation acts during the development of nerves responsible for controlling eye muscles, resulting in movement disorders such as Duane Syndrome, a form of squint.

The findings could provide the key to reversing the condition and unlocking the causes of movement disorders in other parts of the body.

The research is published in Proceedings of the National Academy of Sciences.

As nerves develop in the womb they respond to signals that tell them in which direction to grow. Some signals encourage them to grow to a particular part of the body, while other signals tell them to avoid certain areas.

When the system works as it should, the right type of nerve grows to the appropriate part of the body.

The surface of growing nerves includes identification receptors that respond to signals from secreted proteins. The protein mutated in Duane Syndrome acts as a switch that weighs up incoming signals from the receptors – in this way the nerve knows whether it must grow towards a part of the body or be repulsed away.

Eye Movement Disorders When you look at an object, you're using several muscles to move both eyes to focus on it. If you have a problem with the muscles, the eyes don't work properly.

There are many kinds of eye movement disorders. Two common ones are:

Strabismus - a disorder in which the two eyes don't line up in the same direction. This results in "crossed eyes" or "walleye."
Nystagmus - fast, uncontrollable movements of the eyes, sometimes called "dancing eyes"

Some eye movement disorders are present at birth. Others develop over time and may be associated with other problems, such as injuries. Treatments include glasses, eye muscle exercises, and surgery. There is no treatment for some kinds of eye movement disorders, such as most kinds of nystagmus.

In conditions such as Duane Syndrome, the signalling breaks down and the nerve cells are unable to distinguish between a signal of attraction or repulsion. As a result, the nerves that control eye movements grow to the wrong muscles causing limited or complete loss of eye movement. If not corrected surgically, this can lead to partial blindness in later life.

This recent research has provided new insights into how this 'switch signal' system works and how it has failed in cases of Duane Syndrome, causing the 'wiring up' of the wrong muscle or 'overshooting' of nerve development past the correct muscle.