Tourette Syndrome, or simply Tourette’s, has historically captured the public eye, and ear, by being simply too bizarre to ignore. It causes sufferers to perform ‘tics’ – brief involuntary actions such as arm movements and fragments of speech. Notoriously, the vocal tics can sometimes be socially inappropriate, e.g. swear words, horrific obscenities or comments on the attractiveness (or otherwise) of strangers.
Seeing these conspicuous examples of how the subconscious brain can affect behaviour helps create the intrigue around this rare brain disorder. However, the mystery is now one step closer to being unravelled.
It’s been known for a while that Tourette’s is largely caused by genetic factors, since children of Tourette’s sufferers are 60-times more likely to have the syndrome. Now, scientists have been able to successfully link specific genes and sections of the genome to Tourette’s.
To identify sections of the genome that influence a trait, scientists simply compare the DNA of people with and without the trait to see what’s different. Simple in theory, but with 6.5 billion base pairs per person and thousands of people to compare with each other, this quickly becomes challenging. Using this approach, scientists at UCLA, London, recently compared 2500 Tourette’s sufferers with 4000 unaffected individuals and identified two genes strongly associated with Tourette’s.
The first, called NRXN1, is associated when it is deleted, suggesting it helps prevent Tourette’s when present. The other, called CNTN6, was associated when duplicated. This suggests that stronger expression of this gene, from the multiple copies, contributes to developing Tourette’s. Both of these genes are involved in creating the complex patterns of neurons that makes our brains work. However, the poverty of our knowledge about these processes means we’re still far from understanding how they contribute to Tourette’s, and psychological disease in general. With NRXN1, for example, the deletion was found in just 12 of the 2,500 Tourette’s cases examined, so in the vast majority of cases the disease develops by a different route. Diseases such as Tourette’s are often caused by many different genes each with a very small effect, all adding together and interacting to produce the observed effect. Astonishingly, this means there are thousands of different ways of producing the very specific behaviour of involuntarily shouting random phrases.
Nevertheless, as we learn more about the disease, we are unravelling its complexity. Identifying genes with strong effects, like NRXN1 and CNTN6, will hopefully lead us to understand the mechanism by which the disease develops, that can then be applied more broadly to all Tourette’s cases. Therefore, with this first discovery of Tourette’s-causing genes, the clock is now truly ticking on this oppressive, yet fascinating, psychological disorder.
This article was written by Isaac Shaw and edited by Sam Stanfield.