Seeking a genetic link to anorexia nervosa

Evidence is convincing enough for the U.S. government to have begun a search for genes

Anorexia nervosa is a difficult disease to understand, causing people to starve themselves or see themselves as fat when they're actually underweight.

Many theories on the cause of anorexia have been floated, from parenting practices to cultural forces that pressure girls to be thin. But researchers now believe that the baffling, dangerous disorder has its roots in biology, that genes make some people vulnerable.

The evidence is convincing enough that the U.S. government has begun a search for these genes. The five-year, $10-million study includes families in which two or more members, mainly siblings, have anorexia.

Researchers are conducting extensive interviews with the participants and taking blood samples that will then be analysed to look for genes that might increase susceptibility. The study, in which 400 families eventually will be enrolled, is funded by the National Institute of Mental Health.

Although scientists don't believe a single gene causes the disease, they do suspect that a number of genes cause personality traits common to people who develop anorexia. These obsessional traits include perfectionism, anxiety and social phobia.

"People with anorexia have pretty much the same behaviours," said Dr. Walter H. Kaye, a psychiatry professor at the University of Pittsburgh and one of the principal investigators of the study. "They probably resemble each other more than people do in any other behavioural disorder."

Some of the traits, said Kaye, are observed in childhood, well before the emergence of the eating disorder, which often occurs in adolescence. Researchers have also long observed that eating disorders seem to run in families, and several studies of twins show what appears to be a strong genetic basis for the illness.

A study by University of California, Los Angeles, researcher David Strober, published in 2000, found that although the rate of anorexia nervosa among American women and older girls is 0.1 per cent to 0.5 per cent, the rate of the disorder in female relatives of people with the disorder is three per cent - 10 times higher.

All this points to genes, said Kaye, although genes alone don't explain why some people develop anorexia and others don't.

"Behaviour is always some mixture of biology and environment," said Kaye. "And, clearly, not everyone with these traits ends up with anorexia nervosa."

Researchers believe that one or more genes on chromosome 1 may be responsible for the obsessional traits.

Linking particular genes to these traits might some day yield better treatments for the disease, which is extraordinarily difficult to treat and eventually kills up to 20 per cent of sufferers.

"It's conceivable there are genes involved in weight regulation, and genes likely play a role in compulsive behaviour," said Strober, a professor of psychiatry at the UCLA David Geffen School of Medicine and director of the eating disorders programme.

"If you identify those genes and put the pieces of the puzzle together, then you may be able to develop novel drug therapies that correct this type of behavioural abnormality, or at least blunt its impact. So the implications for therapy are limitless," he said.

What Is anorexia nervosa?

Anorexia nervosa is a type of eating disorder that causes self-starvation. Facts about the disorder:

- It has five primary symptoms: refusal to maintain normal body weight; intense fear of being "fat"; feeling "fat" despite weight loss; absence of menstrual periods in post-puberty girls and women; extreme concern with body weight and shape.

- Between five per cent and 20 per cent of sufferers die of the disease. The risk increases depending on the length of the condition.

- It typically appears in mid-adolescence and is much more common among women.

- It can damage the heart muscle, reduce bone density and cause dehydration, overall weakness and dry hair and skin.