Video: Mirror movements
A handful of rare individuals have 鈥渕irror movement鈥� disorders: they are unable to clench their left fist without the right following suit.
Now a gene that causes such disorders has been found, and it may help unravel a deeper mystery: how it is that the left side of our brains controls the right side of the body, and vice versa.
Mirror movement (MM) disorders fascinate neuroscientists because they appear to arise from the sides of the brain failing to connect to just one side of the body. Studying them might therefore tell us how the left-right links normally form.
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鈥淚t鈥檚 a problem where the brain, instead of being selectively connected to the opposite side of the body, seems to connect to both sides of the body,鈥� says , a neurologist at the University of Montr茅al in Canada.
Misdirected nerves
To understand the genetic basis of MM disorders, Rouleau and his colleagues scanned the genes of members of several generations of a Canadian family in which mirror movement is common.
Those with MM disorders had a specific mutation in one of their copies of a gene called DCC, thought to control the routes that the developing nerve cells carve through the body.
His team found a different mutation in the DCC gene in an Iranian family in which the disorder is common, but in none of 538 unrelated people without mirror movements.
The team concludes that DCC protein is required during development to coax nerve cells across the body鈥檚 midline, so that left brain areas control the right side of the body and vice versa. In people with just one working copy of DCC, only some nerve cells get the message to cross the midline.
Kanga mice
, a biologist at Jackson Laboratory in Bar Harbor, Maine, says further studies in a mutant strain of mice might reveal more about why this is. The mice, which her team discovered, have a kangaroo-like hop because they can鈥檛 move their left and right legs independently. They produce a shortened form of DCC.
Studying them could offer clues to the changes that underlie mirror movements in people. 鈥淭his paper is quite exciting,鈥� she says. 鈥淲e hadn鈥檛 thought of this as a mirror movement disorder.鈥�
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