These strains are affectionately known as Kanga mice. If mice have mutated and shortened copies of DCC, they too show mirror movements and they move with a distinctive hopping gait. It’s not just humans who are affected in this way. In this case, the mutation was different but the result was the same – a shortened and ineffectual protein. She sequenced their DCC genes and again, she found that those who make mirror movements had broken copies. To confirm DCC’s role, she turned to an Iranian family, many of who also demonstrated the quirk from birth. Srour found this mutation in every case of mirror movements, and never in 760 unrelated people whose left and right sides are typically independent. That chunk happens to include many of the most important segments of the DCC protein, which, in its abridged form, is completely useless. This tiny fault means that the protein encoded by DCC is manufactured with a missing chunk. In the Canadia family, those who make mirror movements have a version of DCC with a single altered DNA ‘letter’. One of these genes is called DCC and it turned out to be the true culprit behind the disorder. 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. Not everyone was affected, and the pattern of the disorder strongly suggested that a single dominant genetic fault was responsible. She studied a large French Canadian family with four generations of members who had been making mirror movements from birth. Now, Myriam Srour from the University of Montreal has found that a single faulty gene can cause the condition. The only exceptions tend to be people with rare genetic disorders of the nervous system, like Klippel-Feil and Kallmann syndromes. Young children sometimes make mirror movements but they almost always grow out of it by the age of 10. In 2002, a Chinese man with the disorder failed to get into the military because he couldn’t use the monkey bars. Doing things like playing the piano or typing are very difficult. Clench the left fist, and the right one closes too. Some people make “ mirror movements ”, where moving one side of the body, particularly the hands, causes the other to move unintentionally. But, surprisingly, not everyone can do this. If you’re like most people, the answer is nothing. What happened to your right hand when you did it?
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