Modern society puts powerful pressure on women to control body weight, penalizing obesity and rewarding thinness in myriad ways. For this reason, some observers say, women suffer from anorexia nervosa -- a disorder in which victims starve themselves, sometimes to death -- at rates 10 times higher than men. Recent studies show, too, that the younger a woman is, the more vulnerable she is to developing anorexia.
Compelling as cultural explanations for the current prevalence of anorexia may be, however, they do not present a complete picture of the disorder and its causes, according to Wade Berrettini, MD, PhD, director of Penn's Center for Neurobiology and Behavior. In a just-published review of studies of anorexic twins, Berrettini found that both members of a pair of identical twin sisters were substantially more likely to suffer from anorexia than were both members of a pair of fraternal twin sisters. Additionally, immediate family members of anorexic women were 10 times more likely to contract the disorder than were members of the general population. Berrettini's review appears in the winter issue of Directions in Psychiatry.
"There's an enormous emphasis on thinness in society's image of female beauty, and most people think a woman's risk of developing anorexia nervosa derives solely from that fact," Berrettini notes. "But studies of twins and families suggest that about half the risk of developing this eating disorder is inherited."
Berrettini is collaborating with Walter Kaye, MD, of the University of Pittsburgh, whose group has collected blood samples from about 200 families in which at least two siblings -- not necessarily twins -- have anorexia or bulimia, a related disorder in which eating binges are followed by self-induced vomiting. Berrettini's team at Penn is now analyzing the DNA extracted from those samples to identify the genetic factors underlying anorexia. The most likely finding, Berrettini says, is that several interacting susceptibility genes are involved.
Treatments available for anorexia are limited in their long-term effectiveness, and patients are prone to relapse. Berrettini suggests that improved therapies might be one eventual result of the discovery of genetic risk factors for anorexia.
"There is not a single government-approved medicine to treat anorexia," Berrettini says. "It's our hope that if we can find susceptibility genes, we will then be able to develop better treatments for the disorder."
An understanding that anorexia is partly inherited would also help lessen the stigma that sometimes attaches to the disease, he observes.
The method Berrettini's team is using to analyze the DNA samples collected is called the affected sibling pair method. It relies on the statistical fact that any two siblings will share, on average, half of their DNA sequences. If multiple pairs of siblings with an illness are found to share a particular region of DNA more often than half the time, it raises the possibility that a risk gene for that illness may lie along that stretch of the genome, prompting the scientists to perform a closer analysis of that segment of DNA.
According to Berrettini, anorexia nervosa is defined as an eating disorder characterized by a refusal to ingest sufficient quantities of food to maintain 85 percent or more of normal body weight, an irrational fear of obesity, and a distorted body image of being overweight when emaciated. Women suffer from anorexia at rates ten times higher than men, and the disorder also occurs most often among women of middle and upper socio-economic standing. Abuse of laxatives and excessive exercise to promote weight loss are common behavioral symptoms among anorexic women. Patients often experience amenorrhea, the suspension of normal menstruation, and mortality is approximately 20 percent over a 20-year period, demonstrating that anorexia nervosa can be a deadly disorder.
The University of Pennsylvania Medical Center's sponsored research ranks fifth in the United States, based on grant support from the National Institutes of Health, the primary funder of biomedical research in the nation -- $149 million in federal fiscal year 1996. In addition, for the second consecutive year, the institution posted the highest growth rate in its research activity -- 9.1 percent -- of the top ten U.S. academic medical centers during the same period. News releases from the University of Pennsylvania Medical Center are available to reporters by direct e-mail, fax, or U.S. mail, upon request. They are also posted electronically to the medical center's home page (http://www.med.upenn.edu) and to EurekAlert! (http://www.eurekalert.org), an Internet resource sponsored by the American Association for the Advancement of Science.