There is the risk that people with eating disorders will read about this and feel they are deficient and defective in some way

Nicky Bryant, chief executive, Eating Disorders Association

So having this gene might significantly increase the risk of developing an eating disorder.

Dr Collier said: "Anorexia doesn't seem to be a disease of dieting, it has a deeper biological cause, and perhaps many factors that trigger it are family factors from an early age."

Eating disorders are commonly thought to have a psychological root, with perhaps more than one trigger.

Media obsession

Some blame them on a perceived obsession in the media, and society generally, with images of thin women.

Dr Collier: 'biological cause'

Nicky Bryant, the chief executive of the Eating Disorders Association, said that the gene theory was still unproven.

She said: "There is the risk that people with eating disorders will read about this and feel they are deficient and defective in some way.

"There are a range of different factors which contribute to eating disorders. This is an interesting study but much more needs to be done."

Dr Paul Flower, from the Rhodes Farm Clinic in north London, who specialises in treating adolescents with eating disorders, said that finding genetic markers would be a valuable clue.

He said: "It will help us understand more about what processes cause this problem, and help us focus our psychological treatments."

The conference is hearing from other scientists conducting research into why people develop eating disorders.

Janet Treasure, also from the Institute of Psychiatry, believes that a physical mechanism may contribute to the "emotional" response of disgust when confronted with food.

And Barbara Rost from the University of Basle in Switzerland believes she has spotted differences in the structure of the brains of people with eating disorders.

She used a MRI scan to compare them to people who do not have eating disorders.

It is not clear, however, whether these structural differences are the cause of the condition or arise as a result of it.