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.

Mirror, Mirror, in the Brain

Marion says her condition doesn't affect her life greatly, that she can do her "daily work" just fine.

But others with this condition are not so lucky.

In order to isolate the gene responsible for this condition, researchers studied families where the phenomenon was common, but where there were no other symptoms -- patients like Marion.

For many of those who suffer from mirror dystonia, however, the condition is just one of a collection neurological dysfunctions that impair day-to-day functioning.

Stacy has only had one patient with this disorder in his 20 years of practice, but for that patient the condition was debilitating and an endless source of frustration.

"She couldn't write," he says. "Every time she would try to grab a pencil, the other hand would grab it also. She could walk but struggled with every step."

It didn't help his patient that many doctors are not familiar with the rare condition and hence do not take it seriously, he adds.

"Her teachers thought she was being obstinate and acting out. She eventually dropped out of school," he says. "Now that the gene that causes this is identified ... it will be easier to say, 'This woman has a medical syndrome, she needs to be taken seriously.'"

Mirroring movements can be seen more commonly in the hands, feet and forearms of children, but it is rare for the issue to persist past age 10. When it does, it is often an accompanying symptom to other disorders, such as autism or rare disorders such as Kallmann's and Klippel-Feil syndromes.

Because the condition is so rare and most often is not debilitating, the main aim of this research was not to work towards a cure, Rouleau says. Instead, researchers used the condition to understand how genes control the way the brain controls movement.

By looking at an Iranian family and a Canadian family, both of whom had the condition in several family members, Rouleau and colleagues were able to identify that the gene mutation DCC (Deleted in Colorectal Carcinoma) is responsible for familial cases of mirror dystonia.

Gene Reveals Brain Know-How

Everyone has two copies of this gene, Rouleau says, but those with mirror dystonia have one faulty one.

The gene is responsible for making a protein that tells the brain to "switch" signals so that the right brain controls left side movements and vice versa. Because those with a faulty gene can only produce half as much of the protein, signals to move don't all switch sides in the brain and both sides of the body end up being told to do a task that was meant for one side.

"This tells us what controls the switch in the communication between the brain and the limbs," Rouleau says, which furthers neurologists understanding of the brain.

"Why we are cross-wired this way in the first place," he says, remains a mystery.

Though the new knowledge will not help those with mirror dystonia, Marion is not too concerned.

"It doesn't affect my life," she says, but if her and her family's contribution "makes the science evolve, that's pretty cool."