Mirror Movement Disorder

If you sit down at a piano, hitting different notes with each hand would be the first step to master the instrument. But what if both hands are intent on doing the same thing? That’s the experience of people with a rare condition known as mirror movement, and doctors have now documented a unique case.

Several years ago, researchers in India identified a case of this extremely rare condition in a 13-year-old girl who also has a diagnosis of the chromosomal disorder Turner syndrome.

Finding the two conditions together is a first for the medical community, raising questions of how – or even whether – the two might potentially be connected.

Most tiny humans take a while to become dextrous, but by age 10 the communication between the two halves of our brain allows us to pinch, poke, wave and wiggle the fingers on each hand independently of one another.

For about one in every million children, this development is incomplete, meaning one hand’s actions are echoed simultaneously by the other. Make a victory sign with your left hand, and your right will be forced to approximate a similar shape.

The fundamental cause of such copy-cat movement is still largely a matter of speculation, though there’s reason to suspect key nerves in the brain are ‘cross-talking’ as a result of the formation of false synapses between neurons.

In about a third of all cases, mutations in a couple of genes appear to be responsible, impairing development of the nervous system in such a way that instructions from either side of the brain are accidentally transmitted to both sides of the body.

As for the rest of recorded cases, clearly there’s still much to learn about the brain and its development.

One place we can look for more clues is in other symptoms and behaviours exhibited by those with the condition and ask if there is a deeper relationship.

For example, individuals who also have cerebral palsy will display degrees of mirror movements. Parkinson’s disease is another condition that can come with this form of so-called synkinesia, especially if it affects more one side of the brain than the other.

Having breaks or an absence of connection between the hemispheres – a bridge of neurons called the corpus callosum – can also coincide with the behaviour. It’s in many of these cases that a genetic link has been uncovered.

Kallmann syndrome is a condition caused by lack of certain hormones, giving rise to characteristics such as a lack of smell and delayed puberty. And, sometimes, mirror movements.

Turner syndrome is also a condition that impacts on a body’s ability to coordinate hormonal responses.