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 the chief culprit, a 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 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."
The analysis revealed a "truncating" mutation in a gene recently shown to encode for the "ciliary" protein CEP19.
Cilia are finger-like extensions on cell surfaces that have important functions. Moving cilia allow sperm to swim and carry inhaled debris out of the airways. But defects in sensory cilia can lead to diseases affecting the kidney, liver, pancreas and bones, as well as obesity.
When scientists deleted a version of the CEP19 gene in mice, the animals became obese.
The research is published in the American Journal of Human Genetics.