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Canadian researchers have found a gene they believe is involved in burning calories, which could lead to new therapies for obesity.

Researchers from Toronto, Chicago and Spain say they have identified a gene that appears to be responsible for how humans expend energy and regulate body composition.

"This is a gene that is really the hidden fat gene," said Chi-Chung Hui, co-lead author of the study based at Toronto's Hospital for Sick Children.

In the study, researchers used mice to study the FTO gene, which has long been linked to obesity. They found that the FTO gene interacts with a gene called IRX3, which is far away on the genome. Humans and mice have these genes in common.

Dr. Hui said IRX3's apparent role in how energy is burned was previously unknown.

When the researchers inactivated the IRX3 gene in a group of mice, the animals gained less weight than others in which IRX3 was intact. Dr. Hui, who is head and senior scientist of the developmental and stem-cell biology program at SickKids, said mice without the IRX3 gene had more brown fat, which is believed to burn calories faster than white fat.

Dr. Hui said the gene likely has relevance to obesity in humans. But, he added, the relationship is not yet clear.

Further research is needed to get a better understanding of the mechanism by which IRX3 works, and what other genes or processes are involved.

Robert Screaton, Canada Research Chair in apoptotic signalling (the science of how cells respond to signals), and a senior scientist at the Children's Hospital of Eastern Ontario Research Institute, doubts scientists will ever find a single gene responsible for obesity.

"[It's] highly unlikely you can find one gene you can dub in that way," said Dr. Screaton, who was not involved in the study. The answer is probably very complex, involving the interaction of a large number of genes, he added.

Gregory Steinberg, Canada Research Chair in metabolism and obesity at McMaster University in Hamilton, said the study seems to indicate that IRX3 plays a role in how energy is regulated. It is possible that future therapies could target that gene to help people burn energy.

But he warned that developing drugs that promote energy expenditure could have negative consequences elsewhere in the body, such as the heart.

One-quarter of all Canadian adults are obese, and the health problems associated with that, including type 2 diabetes, heart disease and stroke, are a major threat to individuals as well as a costly burden for the health-care system.

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