Andr�e Marion demonstrates her mirror movement syndrome. Her hands mirror the movement of each other in all actions, such as brushing her hair.Christinne Muschi
When Andrée Marion brushes her teeth or combs her hair with one hand, her other one makes the same motion at the same time. When she fishes for change in her pocket with her left hand, the fingers on her right hand look like they are crawling.
Many members of her large Quebec family, including her 19-year-old son, make the same kind of involuntary mirror movements, and now Ms. Marion knows why. They have a rare genetic mutation that affects the development of the nervous system.
Normally, the right side of the brain directs the muscles on the left side of the body and vice versa. But in the case of family members with the mutation, the signals go to both sides, says the University of Montreal's Guy Rouleau, a senior member of the team of scientists that studied Ms. Marion's family.
The work on the genetically unusual Marions is an important step toward understanding how the human brain and body are wired in the womb and early infancy, says Dr. Rouleau, and may help shape future therapies that could involve using stem cells to replace or repair damaged brain cells and nerves.
Like most of the 11 affected members of her family, Ms. Marion has mirror movements in her fingers and hands. Three of her relatives, however, also get them in their toes and feet.
When Ms. Marion is brushing her teeth with her left hand, her right hand makes the same motion but doesn't come up to her mouth, moving at her side or wherever it happens to be.
Usually, the movements involve small muscles. She has no problem driving a car or skiing, but can find it tricky to carry a steaming cup of coffee - when the other hand does another chore, the coffee-carrying hand moves in unison.
"If I am running around with a cup of coffee, I'll spill it," says the 47-year-old accountant, who lives in Saint-Sauveur, north of Montreal.
Sometimes she can override the movements - when she is typing with both hands, for example.
Like the others in her family, she first saw it as quirk, nothing to ask a doctor about. Then one of her cousins, suffering from an unrelated problem, consulted a Montreal neurologist, who noticed the mirror movements and was intrigued to hear other family members also experienced them.
A research team approached family members, who agreed to be examined and give blood samples. This allowed the scientists to zero in on a genetic mutation called DCC. It results in the production of an aberrant version of a protein that helps guide the ends of developing nerves across the body's midline. It works like a traffic cop, telling the nerves which way to go.
Laboratory mice with a similar mutation are called "Kanga" mice because they hop rather than walk. This is the first study to show a role for the DCC gene in the human nervous system, say the researchers, who reported their findings in the journal Science.
They have traced the mutation back four generations.
It is a dominant gene - one copy is enough to cause the movements. But some in the family carry the gene and don't have mirror movements, a genetic phenomenon called "incomplete penetrance."
These carriers, like Ms. Marion's mother, may have another protective gene, the researchers say. Hormones may play a role, since men in the family seem to be more affected than women.
Half of them are able to partly suppress the movements, like Ms. Marion, and one family member became an electrician. A number reported being clumsy during childhood, says Myriam Srour, a graduate student who works with Dr. Rouleau on the project. Others said they are embarrassed by the involuntary movements.
But Ms. Marion says she isn't embarrassed. Many of her friends have never noticed the motions. Her biggest regret, she says, is that she can't play pool.