An international team that just conducted the largest study of Tourette syndrome has identified genetic abnormalities that are the first definitive risk genes for the disorder.

Although Tourette has long been thought to have a genetic basis – because the syndrome tends to appear in families – before now no definitive risk genes had been found. The breakthrough came when researchers focused on a relatively new area of genomics research that takes a broader look at the entire genome, rather than searching for a particular gene, says Peristera Paschou, Purdue University associate biology professor.

"Most times we focus on a mutation of a single base pair, which are the building blocks of DNA, and look for a mutation. But in recent years we've realized that there is another type of variation of the human genome," Paschou says.

Scientists have been exploring how often short sections of genes are repeated through the entire genome, how these repetitions might vary among individuals, and whether these repetitions, which are called copy number variants, have an effect on health.

"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," she says. "In the case of this research on Tourette Syndrome, we scanned the entire genome, and through physical analysis, we were able to identify where this variation lies.

"We rarely find variants that are associated at such a high level. This is why this is such a big breakthrough." Dr. Jeremiah Scharf, of the Psychiatric & Neurodevelopmental Genetics Unit in the Massachusetts General Hospital Departments of Psychiatry and Neurology and the Massachusetts General Hospital Center for Genomic Medicine, co–senior author of the report, says this is a significant finding.

"The challenge of recognizing that Tourette Syndrome is not a single gene disorder, and that a stringent statistical certainty is required in order to declare a gene to be significantly associated with it, has been our long–term aim," he says. "We believe that what sets our study apart from prior studies is that the two genes we have identified both surpassed the stringent threshold of ‘genome–wide significance,’ and so, represent the first two definitive Tourette Syndrome susceptibility genes."

The research was published in the journal Neuron.