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.
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."