It's not uncommon for individuals to consult their family trees to evaluate their predisposition to various illnesses, including heart disease, cancer and obesity. But a disease that tends to be absent from the checklist of dangerous and highly-inheritable illnesses to look for in family medical histories is eating disorders.
The link between genetics and eating disorders
Most people don't understand the connection between genetics and eating disorders when, in fact, there is a very strong genetic component to these illnesses.* Research has found that 40 to 50 percent of the risk of developing an eating disorder is based on genetics. Anorexia nervosa, an eating disorder characterized by extreme low body weight and a refusal to consume sufficient calories to support bodily functioning, has been found to be as inheritable as bipolar disorder and schizophrenia.
Family studies have also supported the genetic link of eating disorders. Compared with the general population, a woman with a mother or sister who has anorexia is 12 times more likely to develop the disease and four times more likely to develop bulimia nervosa. Twin studies have perhaps shed the most meaningful light on the heredity of eating disorders. Among identical twins, whose genetic makeup is 100 percent the same, there is a 59 percent chance that if one twin has anorexia, the other twin will also develop an eating disorder. Among fraternal twins sharing only 50 percent of their sibling's genes, the incidence of the illness in both twins was lower but still significant. When one twin has anorexia, there is an 11 percent chance that the other twin will also have the illness.
What exactly do you inherit when it comes to eating disorders?
While research to date has helped bring to light the connection between eating disorders and genetics, there is still much to understand, specifically what is inherited. Studies from both the Maudsley Hospital in London and the University of Pittsburgh suggest that variations in the gene for serotonin receptors may play a role in the development of eating disorders. Abnormal serotonin levels are associated with overall more negative moods and obsessions with perfectionism and exactness.**
Another hypothesis, from my colleague Emmett R. Bishop, Jr., M.D., FAED, CEDS, medical director of adult services at Eating Recovery Center, proposes that the link between genetics and eating disorders may lie in personality traits passed down from one generation to another. This theory is rooted in the understanding that tendencies toward personality traits commonly seen in eating disordered individuals, including perfectionism, negative emotions, obsessive thinking, anxiety and impulsivity, have been found to be at least partially the result of genetic expression.***
While a genetic predisposition can play a meaningful role in the development of eating disorders, it's important to clarify that not all individuals with family histories of anorexia and bulimia will develop a form of the illness. When asked what causes eating disorders, I like to tell patients and families that "genes load the gun, and life pulls the trigger," meaning that a perfect storm of biological, psychological and sociological factors must align to cause an eating disorder. In some cases, non-biological triggers can spark the onset of these illnesses in someone with no genetic link to eating disorders, including trauma, a diet gone awry or societal pressures. However, there is certainly value in understanding the interplay between genetics and eating disorders and evaluating your risk based on family history.