Researchers have conducted the first genome-wide search to look for any genes responsible for Tourette syndrome and obsessive-compulsive disorder (OCD). Findings show that neither OCD nor Tourette syndrome are simple enough to be traced to a single problem gene, but the researchers have been able to pinpoint several areas on the human chromosome that may contribute to the conditions.
“Both disorders clearly have a complex underlying genetic architecture, and these two studies lay the foundation for understanding the underlying genetic etiology of Tourette syndrome and OCD,” said Dr. Jeremiah Scharf, a neurologist at Massachusetts General Hospital in Boston, who worked on both projects.
In the Tourette syndrome study, researchers compared the genomes of more than 1,200 people with the disorder to the genomes of nearly 5,000 healthy individuals.
They carried out a “genome-wide association study,” which includes scanning hundreds of thousands of genetic variants across the genomes to see whether any were more common in people with the disorder.
No single genetic signal was found to be significantly different between the two genomes, meaning that the researchers could not rule out random chance as the reason for any given difference.
However, among the top genetic variations, there was an unusually high number of variations in the frontal lobe of the brain— a region implicated in both Tourette syndrome and OCD, said Scharf.
One gene in particular that had a strong variation between Tourette- and non-Tourette genomes was called COL27A1, which encodes a collagen protein found in cartilage. The same gene is also active in the cerebellum, a brain region important for motor control during development. More research is needed to find what link, if any, this gene has to Tourette syndrome, Scharf said.
In the OCD study, researchers conducted the same analysis on healthy genomes as well as about 1,500 people with OCD. Again, no one gene stood out as a definitive OCD gene, but the findings show a good candidate near a gene called BTBD3, which is involved in multiple cellular functions.
This first genome-wide results are bound to turn up some false positives, noted Scharf, so researchers will now need to study these intriguing genes in larger samples of people.
Scientists are also comparing the two studies to identify any genetic linkages that might explain why Tourette syndrome and OCD so frequently appear together.
“The important thing this study does is that it really brings Tourette syndrome and OCD into the company of a number of other psychiatric diseases, which people have studied using genome-wide association,” Scharf said, citing autism, schizophrenia and bipolar disorder as examples.
“Now that we have these data for Tourette syndrome and OCD, we can work with investigators who are studying those other diseases to try to see what we can learn about what variants are shared between different neurodevelopment disorders.”
Source: Molecular Psychiatry