A single "fat gene" may be to blame for severe obesity that runs in families, new research suggests.
Inherited factors are known to be important in 40pc to 90pc of cases of obesity. Now scientists believe they have tracked down what may be the chief culprit, an ancient gene that has been around for hundreds of millions of years.
The gene, known as CEP19, appears to play a critical role in regulating energy balance and appetite, and is also linked to male fertility.
When it functions properly, it helps keep the body lean. But mutant versions of the gene may lead to a propensity to obesity that passes from one generation to the next.
Researchers uncovered CEP19 after investigating a large Arab family afflicted by health-threatening obesity.
Dr John Martignetti, a member of the team from the Icahn School of Medicine at Mount Sinai in New York City, said: "Starting with gene discovery in a single family with morbid obesity, these studies led to the identification of a gene that seems to be fundamental to regulating nutritional status.
"This gene is shown to be present not only in humans and mice but also in the simplest known single-cell animal.
"Nature considers this gene so important that it has preserved its structure for more than 700 million years."