Anorexia 'caused by immune defect'

Eating disorders include anorexia and bulimia

A defect of the immune system may be to blame for some cases of the eating disorders anorexia and bulimia.

Scientists have found evidence that the conditions may be the result of autoimmune disorders similar to those that are thought to cause multiple sclerosis and rheumatoid arthritis.

The cause of eating disorders is unlikely to be anything obvious, but lots of different subtle little things

Dr Frances Conan

The researchers, from the Karolinska Institute in Stockholm, analysed blood samples from women diagnosed with anorexia, bulimia or both conditions for the presence of immune system chemicals called antibodies.

In normal circumstances antibodies attack infections and other foreign bodies that pose a threat to the body.

But when things go wrong they can turn against the tissues of the body itself.

Brain structures

The researchers found that most of the patients produced antibodies that attach themselves to cells from two structures found in the brain - the hypothalamus and the pituitary gland.

Both secrete chemicals that regulate the body's metabolism.

It is unclear if or how the antibodies affect the brains of women with eating disorders.

But the researchers suggest that the antibodies could directly destroy, or indirectly interfere with, brain signals that regulate food intake and body weight.

However, they stress that the presence of the antibodies does not guarantee that somebody will develop an eating disorder.

The same antibodies were found in a small number of healthy people.

Complex conditions

Dr Frances Conan, an expert on eating disorders at the Vincent Square Clinic in London, told BBC News Online it was likely that the conditions were caused by a complex interaction between biological, psychological and social factors.

"The cause of eating disorders is unlikely to be anything obvious, but lots of different subtle little things.

"Most people agree that it is probably a combination of genetic inheritance and early experiences of life, both psychological and social, that combine to create a biological and psychological vulnerability to the illness.

"But there are lots of reasons why the hypothalamus and pituitary gland might be involved as they regulate appetite and body image."

The research is published in the Proceedings of the National Academy of Sciences.