Large study finds first genes linked to Tourette's syndrome

The first genes linked to Tourette's syndrome have been identified in the biggest study of the disorder to date.

An international team of researchers scanned the genomes of nearly 6500 people and identified two genes which significantly raise the risk of developing the syndrome.

'We know that Tourette syndrome runs in families, but over the course of the last 25 years it’s been incredibly difficult to identify any genes definitively,' said Dr Jeremiah Scharf of Massachusetts General Hospital and co-leader of the research effort to the Boston Herald. 'This is really setting the stage for how this might be treated in the future.'

Tourette's syndrome is a neurological disorder characterised by involuntary movements and verbal outbursts, which affects around one in 100 people. Multiple genes contribute to the development of the disorder but these can differ between individuals, many of whom frequently exhibit other neurological disorders including attention deficit disorder and obsessive compulsive disorder. These factors have made it difficult to identify genes specifically associated with the development of Tourette's syndrome.

The study, published in Neuron, was conducted by 57 researchers from 11 countries, who analysed the genomes of 2434 people with Tourette's syndrome and of 4093 healthy controls. Instead of looking for a mutation in a specific gene, the scientists looked for copy number variations, which are repeats of sections of DNA.

'These variations may involve a large part of the DNA sequence and may even include whole genes. We have only very recently begun to understand how copy number variation may relate to disease,' said Dr Peristera Paschou of Purdue University, co-leader of the study.

They identified rare mutations in two genes, NRXN1 and CNTN6, as being associated with an increased risk of developing Tourette's syndrome. Approximately one percent of individuals with Tourette's syndrome were shown to carry one of these mutations.

'While [one percent] may sound like a small number, for a complex trait like Tourette, it’s significant,' said Dr Scharf.

These genes are involved in brain development and produce substances that enable brain cells to form connections. CNTN6, in particular, is associated with neuronal connections involved in the control of movement, and this is the first time copy number variants in this gene have been linked to a disease.

The scientists plan to pinpoint which brain cells are not functioning correctly in people with Tourette's syndrome using animal and cellular models to investigate these genes. They are also planning a larger study of 12,000 patients.