Clench your left hand into a fist. What happened to your right hand when you did it?
If you’re like most people, the answer is nothing. But, surprisingly, not everyone can do this. Some people make “mirror movements”, where moving one side of the body, particularly the hands, causes the other to move unintentionally. Clench the left fist, and the right one closes too. Doing things like playing the piano or typing are very difficult. In 2002, a Chinese man with the disorder failed to get into the military because he couldn’t use the monkey bars.
Young children sometimes make mirror movements but they almost always grow out of it by the age of 10. The only exceptions tend to be people with rare genetic disorders of the nervous system, like Klippel-Feil and Kallmann syndromes. Now, Myriam Srour from the University of Montreal has found that a single faulty gene can cause the condition.
She studied a large French Canadian family with four generations of members who had been making mirror movements from birth. Not everyone was affected, and the pattern of the disorder strongly suggested that a single dominant genetic fault was responsible. Srour tracked it down by comparing the genomes of affected and normal family members, and her search led her to a short area on the 18th chromosome, which contained three genes.
One of these genes is called DCC and it turned out to be the true culprit behind the disorder. In the Canadia family, those who make mirror movements have a version of DCC with a single altered DNA ‘letter’. This tiny fault means that the protein encoded by DCC is manufactured with a missing chunk. That chunk happens to include many of the most important segments of the DCC protein, which, in its abridged form, is completely useless.
Srour found this mutation in every case of mirror movements, and never in 760 unrelated people whose left and right sides are typically independent. To confirm DCC’s role, she turned to an Iranian family, many of who also demonstrated the quirk from birth. She sequenced their DCC genes and again, she found that those who make mirror movements had broken copies. In this case, the mutation was different but the result was the same – a shortened and ineffectual protein.
It’s not just humans who are affected in this way. If mice have mutated and shortened copies of DCC, they too show mirror movements and they move with a distinctive hopping gait. These strains are affectionately known as Kanga mice. If they lack any copies of the gene entirely, their problems are more severe. The gap between the brain’s hemispheres doesn’t develop properly and the fibres that connect the two halves– the corpus callosum – are fewer in number and misrouted.
These mutant mice hint at DCC’s role. The DCC protein is a docking bay (a receptor) for another protein called netrin-1, whose role is to guide the neurons of the developing nervous system across the midline of the body. Its name even comes from the Sanskrit word “netr”, meaning “one who guides”. But this neural shepherd can’t stick to broken DCC proteins and without its good work, the neuronal connections between the body’s two halves don’t form properly.
Reference: Science http://dx.doi.org/10.1126/science.1186463
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April 29th, 2010 at 9:00 pm
This is totally weird. I always have to test everything, so I clenched my left fist. The right did nothing. Good.
But I played around a bit; mostly, each hand is independent, but when I separate the two middle fingers of the left hand, the right hand fingers follow suit.
I tried relaxing both hands, then repeating the movement. The right hand always copies the left. When I concentrate on not moving the right hand, I can see tiny movements of the muscles in the right. The same happens when I close the gap on the left.
The left hand does not copy the right, when I reverse the order.
No other hand movement gets copied.
Weird.
April 30th, 2010 at 3:55 am
Susannah: that happens to me too! (same thing: right copies left, but not the other way around).
Also an interesting story.
April 30th, 2010 at 10:27 am
How do they masturbate?
May 14th, 2010 at 9:44 am
Susannah, Joel:
Similar observation for me, but in both directions. The un-repressed mirroring is significantly weaker than the identend movement, but covers 1-2cm (at the finger tips). If I concentrate, a slight twitch remains.
July 17th, 2010 at 12:08 am
My family has this genetic condition. I am the only girl to get it, and it is very upsetting.
July 20th, 2010 at 9:02 am
I have a daughter who is 9 1/2 and for most of her life we have noticed this with her but we have never really thought any more of it, until last few days! we always laughed with her to and said to her that she could colour pictures twice as fast and daft things like that but now i’m feeling guilty after reading Amy’s input. So really just wondering should i go to doctors or anything? or is there anything i can do?
Any advice will be great
Thankyou
August 3rd, 2010 at 10:26 pm
me and my brother where both born with this, one hand copies the other and i am now 16 and he is 19, apperently we will never grow out of it, there is no sign of it in our family history and doctors would not believe my mother during the first few years of our lives. when we where young two americans came to our home in northern ireland to film us and make a documentery about it, ive never seen this recording and would like to. if anybody comes across is please let me know. my name is cameron ward and my brothers is conor. thank you
November 28th, 2010 at 1:10 pm
when i clench my hand the other clenches too. i have this problem from my childhood. Now i’m a surgeon and this is my most kept secret… If you interested write me voverukas@hotmail.com
April 5th, 2011 at 5:11 pm
My brother and i have this condition. So do many cousins and my daughter, niece and nephew. The best suggestion i can offer is to do things like learn to play piano and type and play basketball (dribbling can be interesting!) Some things are harder for me but this condition has never stopped me from being able to do whatever i want to do. I have learned ways to hide it. But mostly nobody ever notices unless i point it out.
April 13th, 2011 at 9:47 pm
I have this condition as well, and it’s never affected anything I wanted to do. it’s never really bothered me. I play guitar, keyboards, video games and type no problem. the only problem I have is being ridiculed by my wife on a daily basis lol.
May 11th, 2011 at 2:49 pm
OMG! I have been dealing with this since I was a child and finally know what it is. I got picked on as a child when others noticed, but have learned how to adapt for it. It affects some things I do, but for the most part, I can control it.
June 1st, 2011 at 4:12 pm
I have this problem too. Over the years I have had trouble, and fun with it. I must set a cup down when pouring milk, or coffee. I can’t hold a board still while cutting it, and etc.
I can have someone squeeze my left, or right hand, and while moving the other hand they can feel and see it moving without my uncontrol.
August 29th, 2011 at 9:00 pm
I also have this – in school my left hand would follow my right hand across the paper as I wrote. The teacher made me sit on the left hand, didn’t stop the movement though. Got a lot of teasing.
I have found that the tenser or tireder I am that this becomes worse.
I have worked hard at concealing it from others.
Now at 61, I am back in school and taking a keyboarding class that I need for a certification. I have to really concentrate and can only do my best.
Muscle memory is what I hear in my classes for floral design and the keyboarding – not as easy at it sounds.
But having this will not stop me – just trying harder.
October 5th, 2011 at 11:07 am
I too was born with this, as was my father and his mother, my younger brother has it very slightly, but I am by far the worst affected member of my family. It is really annoying however I can hide it when I need to. My party trick is being able to write forward with my right hand whilst writing backwards with my left at the same time. Part of my job involves using a keyboard and whilst I dont type in the usual manner I am just as quick as anybody else. I do look a bit silly when I am brushing my teeth tho.
October 16th, 2011 at 3:54 pm
My boyfriend has this problem. He is 18 and has had this problem as long as he can remember. He can’t move his hand with out the other coping it. I mean its not dramatic copying. I didn’t even notice till he points it out but when he’s writing, the other other hand will move, when he scratches, the other hand will clench up. I mean he works well with it and people rarely notice but I have a question… Is there a long term affect to this???
November 3rd, 2011 at 10:09 am
My husbnd suffers from this and also has terrible back and knee pain and restless leg syndrome. Was wondering if there is a connection?
December 9th, 2011 at 3:14 am
I defiently have this!! So does my brother and my dad! When I pick up heavy things my other hand clenches and I can’t control it no matter how hard I try! When I write the other hand moves and when I brush my teeth I look hilarious!! I Always wondered why I did this ! Trying to get something out my jeans pocket also send my other hand a bit crazy! Is there Anyway I can stop it!?
January 2nd, 2012 at 10:39 am
Hey Lucy and others,
I know your feelings. I’ve had mirror movement (hereditary from my father’s side) since birth and the family knows to watch for it in the kids each generation. It affects me most in the hands, but “shows” itself in most left-right side body movements when I’m not thinking about it. (Yeah, the occassional odd twitches are noticable to others.) I was taken to neurologists when I was 4 at University of Michigan who were fascinated by it. It was a pain (sometimes literally like when you drop things on your foot) as a kid myself and I did have some early ed teachers who were very cruel when it took me longer to figure out how to do the same things other kids did. I took piano for 7 years, practiced like crazy typing (got up to 75 wpm), and just stubbornly kept at a task (took months to tie shoes) to develop the concentration needed to be pretty dextrous– just in my own way. (So kudos to the surgeon up commenting earlier, great job!)
Take heart folks, it’s all in how you work with it. Besides, it does make an astonishing party-classroom trick when you can write you name forward and backward at the same time.
Now that I’m older,and a teacher myself, I kind of find it an odd blessing. I’m VERY adaptable, a creative, independent learner, and I have loads of empathy and patience when helping kids find their own way to get a job done. I don’t think I’d be half as good a teacher without it. (So take that early-ed mean teacher
January 15th, 2012 at 6:31 pm
I was born this way and I always tried to find answers. It’s good that I found this website. I too could not do the monkey bars during basis training. People make fun when they see my hand move when I get change from my pocket or when I throw darts at the bar. I’m 37 and it doesn’t seem like it will ever go away.