TULSA, OKLAHOMA: A researcher at a US clinic says that a decade-long study into anorexia nervosa is beginning to reveal that those who suffer from the disease might have a genetic predisposition toward it.

The study, known as the Genetics of Anorexia Nervosa collaboration, is conducted in eight cities in North America and two European cities. It is funded by the National Institutes of Health.

Researcher Craig Johnson said that if a person has a family member who has had anorexia nervosa, he or she is 12 times more at risk of developing the illness.

"Genetics loads the gun. Environment pulls the trigger," said Johnson, the director of the eating disorders unit at Laureate Psychiatric Hospital in Tulsa and one of the study's principal researchers.

Johnson said researchers have devoted much attention during the past 40 years into looking into how a culture that promotes dieting provokes eating disorders.

"We now know that the illnesses occur when there is a perfect storm of events that include genetic vulnerability and a culture that is promoting thinness through dieting and exercise," he said.

People with anorexia nervosa - most of them young females - develop a strong aversion to food and have a distorted body image.

Johnson said the research has helped to identify groups most at risk of developing the disease, such as girls ages 11 to 14.

"Girls are expected to gain a third of their adult weight during that time," or about 40 pounds, he said.

"If a young woman is uneasy with the weight gain, and a parent, coach, girlfriend or boyfriend says something about their weight, it can provoke an episode of dieting."

Johnson called dieting and exercise "the royal road to eating disorders."