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Tourette Syndrome Risk Tied to Rare CNVs in Two Genes

NEW YORK (GenomeWeb) – Members of an international research team have identified rare copy number changes in two genes that seem to increase a person's risk for Tourette syndrome.

In an effort to understand the neurodevelopmental condition, which is marked by symptoms such as vocal tics and involuntary movements, the researchers compared array-based copy number variant patterns in more than 2,400 individuals with Tourette syndrome and nearly 4,100 without. As they wrote today in Neuron, they saw an over-representation of rare deletions affecting the NRXN1 gene as well as CNTN6 gene duplications, along with an overall uptick in CNVs in the Tourette syndrome-affected group.

Overall, roughly 1 percent of individuals with Tourette syndrome carried a rare CNV in NRXN1 or CNTN6, the team reported, suggesting that one or both of the genes may eventually serve as a feasible treatment target.

"Identifying genes associated with Tourette syndrome is a first, key step in understanding their role in the disease process and ultimately in pointing the field toward possible therapeutic strategies," co-senior author Giovanni Coppola, a psychiatry and neurology researcher at the University of California, Los Angeles, said in a statement.

For their study, Coppola and his colleagues used the Illumina OmniExpress SNP array to genotype 2,434 individuals of European ancestry who were diagnosed with Tourette syndrome and recruited through the Tourette Syndrome Association International Consortium for Genetics or the Gilles de la Tourette Syndrome GWAS Replication Initiative.

The team then considered CNV patterns detected in these cases with those found in 4,093 unaffected control individuals of European ancestry who were profiled with the same array platform. Using information at nearly 9,400 rare CNVs detected in the cases and controls, the group was able to look for Tourette syndrome-associated CNVs and rare CNV burden in general.

Similar to results described in other neurodevelopmental conditions in the past, the researchers saw a significant uptick in CNVs falling in genes in the Tourette syndrome group, particularly when it came to rare CNVs spanning more than a million bases.

Meanwhile, when they focused in on specific CNVs that were more common than usual in the individuals with Tourette syndrome, the investigators uncovered two main loci: chromosome 2 deletions impacting NRXN1 exons that appeared to be specific to individuals with Tourette syndrome and duplications at the CNTN6 locus on chromosome 3 that turned up in a dozen Tourette syndrome cases, but just two control individuals.

"These first two definitive genes for TS give us strong footholds in our efforts to understand the biology of this disease, and future studies of how these genes work both in health and disease may lead to discoveries that are more broadly relevant to neuropsychiatric disorders in general," co-senior author Jeremiah Scharf, a psychiatric and neurodevelopmental genetic researcher affiliated with the Massachusetts General Hospital, the Broad Institute, and Brigham and Women's Hospital, noted in the statement.