Mirror Movement Disorder Forces Limbs to Work in Tandem

Apr. 29, 2010— -- Andree Marion's right hand not only knows what the left one is doing, it is forever mimicking its actions.

When Marion, 47, brushes her teeth with her left hand, her right hand will automatically do an "air brush" impression. When she turns a door knob with her right hand, the left one will twist in kind.

Because of a rare condition known as mirror dystonia, Marion's hands will perpetually act in tandem, but thanks to a University of Montreal study published Thursday in the journal Science, researchers now understand why.

Even if Marion balls the unintended hand into a fist in an attempt to stop the mimicry, "you can feel my nerves are still firing," says Marion, an accountant in Montreal. "It makes me clumsy, and I'm a very bad player at pool. I also have to be careful cutting vegetables so that I don't cut myself."

With the help of Marion and her family members, several of whom also suffer from mirror dystonia, researchers were able to isolate the genetic mutation causes this bizarre reaction -- a discovery they say reveals a lot about how the brain controls movement, in general.

The genetic mutation causes sufferers to create less of a protein that directs brain signals to either the left or right side of their bodies. Because of that, both sides of the body sometimes get the same signal -- though not always with the same intensity.

"In the human brain, the right side controls movement in the left side and vice versa," says Dr. Guy Rouleau, lead researcher on the study. "We don't know why the brain is made this way, but this study gives us a good idea of what makes this switch happen."

"It opens up an array of thinking about the brain," says Dr. Mark Stacy, a professor of neurology at Duke University.

This new knowledge could one day lead to better treatments for the motor problems experienced by Parkinson's patients or those with spinal cord injuries, he says.