Researchers in Australia believe they have discovered a genetic link to the dieting disease anorexia nervosa.

The researchers, who work at the Department of Psychological Medicine at Westmead Children's Hospital, investigated a chemical in the brain which causes anxiety, known as norepinephrine. They discovered a new chunk of DNA, which was present in a number of families with anorexic children and parents.

Lead clinician Kenneth Nunn told United Press International that anorexics might be super-metabolisers of norepinephrine.

"When they go on a diet, these super-metabolizers with the longer form of DNA could use up their supplies too quickly and go into a negative spiral of norepinephrine depletion from which they cannot escape. Once they begin to shut down and eat less, they become even more depleted of norepinephrine," Nunn said.

The study is published in the journal Molecular Psychiatry.