Evidence from twin studies suggests there is a strong genetic component to anorexia nervosa, an eating disorder characterized by a persistent refusal to ingest enough food to maintain a near-normal body weight.
Anorexia nervosa is 10 times more common in women than in men and has become more frequent in recent decades, leading many experts to speculate that the current cultural emphasis on thinness contributes to the disease's prevalence. But a new review of twin studies of anorexia by Wade Berrettini, a professor of psychiatry and pharmacology at the University of Pennsylvania, concludes that about 50% of the risk of developing the disease can be attributed to genetic factors. The review appears in the winter issue of the journal Directions in Psychiatry.
When one twin has a disease, the chance that the other twin will also have it is called the concordance rate. Three studies compared the concordance rate for anorexia nervosa in identical twins (who share 100% of their genes) with that in fraternal twins (who share 50% of their genes, as do any two siblings born to the same parents).
All three studies found that the concordance rate for anorexia was much higher in identical twins than in fraternal twins. The mean rate in identical twins was 59%, compared with 11% in fraternal twins.
Reviewing family studies, Berrettini found that first-degree relatives of individuals with anorexia nervosa had a five-to-sixfold greater risk of developing anorexia or bulimia, an eating disorder characterized by deliberate vomiting or purging, compared with people who had no relatives with eating disorders.
Berrettini suspects that several susceptibility genes may contribute to an individual's risk of anorexia and bulimia. He and his team are collaborating with University of Pittsburgh researchers on a study of blood samples from about 200 families, each containing at least two siblings who have these disorders, in an attempt to identify the genetic factors at work.