A single genetic fault makes one hand mirror the other's movements

By Ed Yong | April 29, 2010 2:00 pm

FistsClench 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

More on genetic disorders:

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Comments (27)

  1. 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.


  2. Susannah: that happens to me too! (same thing: right copies left, but not the other way around).

    Also an interesting story.

  3. Waltz

    How do they masturbate?

  4. Arno

    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.

  5. Amy

    My family has this genetic condition. I am the only girl to get it, and it is very upsetting.

  6. leanne

    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

  7. Cameron Ward

    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

  8. Ed.

    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

  9. heather

    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.

  10. Jeremy

    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.

  11. Gerri

    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.

  12. Stanley Parsons

    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.

  13. Jan Swanson

    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.

  14. Clare

    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.

  15. Holly

    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???

  16. C.Lyons

    My husbnd suffers from this and also has terrible back and knee pain and restless leg syndrome. Was wondering if there is a connection?

  17. Lucy

    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!?

  18. 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!)
    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 😉 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.

  19. mario

    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.

  20. Matt

    3.   Waltz Says:
    April 30th, 2010 at 10:27 am
    How do they masturbate?

    I have this disorder so i guess I’m in a position to answer your question 😛 I have to clench the other hand. By doing so I gain a measure of control over it, it’s quite interesting

  21. KK

    Susannah and Joel,

    I kind of get the same thing except in reverse. Left hand copies right, not the other way around. (I’m left-handed.)

  22. lidia

    I totally have this. Whatever I do with the left it affects the right and vice versa. I had asked a doctor about this and she said its not something to look down on..it can be a privilege, because it means we can be more motor advanced than others. She explained its like your brain is working double sending signals to both of the hands instead of just one. Surprisingly she guessed that I was an artist. She mentioned people that have this are usually artistically skilled or skilled with other motor type activities. So I see it as a blessing heck maybe I can train the other hand to draw at the same time :).

  23. sara

    My son is 11 months old and we have just started noticing the mirror movements he dosent do it all the time thou. He also has a rare genetic disorder called klippell-feil syndrome x

  24. Krista

    My daughter has this, I had her tested for a learning disability and the doctor said that it was linked to her learning disability. I never investigated any further because he said there was nothing we could do about it. As she has gotten older it has begun really bothering her, she is now 16 and seems to get embarrassed about it. She will sit on her left hand to keep it from moving and others from noticing. I don’t think she has ever been teased over it. She wanted a keyboard for Christmas and tried to play it unsuccessfully because of this, I think this is when she really became frustrated over it.

  25. eren

    I turned this mutation into the artistic talent.It’s cool when u draw a picture.So love your talent and use it.It works!

  26. linda

    For a long time I couldn’t work out why our son, now nine and the older of twins, had both hands moving when he coloured in and brushed his teeth. If I ever said anything to him he just sat on his hand, but I could still see it moving under his leg. He has also had trouble tying his laces. The simple fact that we have always had a twin to compare him to has show us how much further behind his manual developement has been. Dont worry, it has never been a big problem for him but it has been great to find a website and a name for it.

  27. Nancy

    I have had this all my life, but no one in my family has it. No one seems to know why. You can go to facebook and search Bimanual Synkinesis to connect with more people with this condition.


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