Neurological disorder of mirror movements: Looking deeper into the mirror

The discovery was made by Kaiyue Zhang, a doctoral student at the Montreal Clinical Research Institute (IRCM), affiliated with Université de Montréal, and by Karina Chaudhari, a doctoral student at the University of Pennsylvania.

As co-first authors, they published their study in the journal Science Signaling.

They were led by Frédéric Charron, an UdeM research professor and director of the IRCM's molecular biology of neuronal development research unit, in collaboration with Greg Bashaw's team at the University of Pennsylvania.

Mirror movement disorder is a poorly understood hereditary neurological disorder that manifests itself in involuntary movements from an early age, mainly in the arms and hands.

In those affected, the right hand involuntarily reproduces the movements of the left and vice versa. The disorder can cause pain in the arms during prolonged activities, and difficulties in performing tasks requiring left-right coordination.

"Mirror movement disorder disrupts the daily lives of affected individuals," said Charron, who's also an adjunct professor at McGill University. "Simple actions such as opening a bottle of water can become difficult, as can playing a musical instrument."

A defect in a phenomenon

The cellular mechanism behind mirror movements is a defect in a phenomenon known as axon guidance.

During embryonic development, neurons extend their axons, a long cellular cable that enables them to link specific areas of the body together, thus establishing nerve connections.

The set of processes that control axon elongation and guide its navigation is called axon guidance. Among other things, axon guidance connects each neuron to its specific target. It is therefore crucial to the proper development of the nervous system.

Various guidance molecules direct axons to their targets, acting like signposts to guide axons to their destination. To do this, these guidance molecules must induce axon movement when they are detected by axons.

This movement requires a complex molecular machinery that is still poorly understood.

In the new study, the researchers showed that the machinery required for guidance is in fact the cytoskeleton, a microscopic skeleton which gives a cell a certain rigidity, rather like the bones of the body which, through their rigidity, enable movement.

Understanding the mechanisms causing mirror movement is key to finding ways to treat it. The work of the Charron laboratory promises new targets in that regard, as well as for other diseases resulting from defects in the development of the nervous system.