It has long been known that eating disorders run in families, but a new study finally pinpoints two genes that significantly increase a person's risk for developing anorexia nervosa and bulimia.
Typically, research has focused on studying a large number of people to find small genetic variants that may contribute to the risk of developing an eating disorder. But scientists from the University of Iowa and the University of Texas Southwestern Medical Center took the opposite approach: they studied single families in which eating disorders were common across generations. They found that people with mutations in two different genes – ESRRA and HDAC4 – had a 90 percent and 85 percent chance of developing an eating disorder, respectively.
"Probably the most useful thing is that it will allow us to study the neurobiology, the underlying cause of eating disorders, and try to find new ways to boost the pathway to prevent them," says Michael Lutter, an assistant professor of psychiatry at the University of Iowa and the senior author of the study.
Lutter says the scientists believe this pathway, where both genes are found, works in the brain to increase a person's desire for food when they have an increased need for calories. But when the genes are mutated, they can block a person's ability to want to eat.
Although the mutations are rare (about one in 1,000 have the ESRRA mutation, and just two in 10,000 have the HDAC4 mutation) they significantly increase a person's risk for developing an eating disorder. In those subjects with the ESRRA mutation, 90 percent developed an eating disorder, and six out of seven people with the HDAC4 mutation had one.
What's more, Lutter says the people who had the mutations but did not show signs of an eating disorder were very young. "It might just be that they're not old enough yet to develop it," Lutter says.
Eating disorders are also particularly common among women: anorexia nervosa and bulimia nervosa affect between 1 percent and 3 percent of women, the study says.
Leslie Sim, a clinical child psychologist at the Mayo Clinic, says these findings could provide relief to families and parents, who often blame themselves for a child's eating disorder.
"We're really starting to see this as a true biological illness, where essentially we're seeing these kids sharing these temperament predispositions that likely places them at risk," says Sim, who serves as the clinical director of the Mayo Clinic's eating disorders program. "So often parents are really looking for what they did to cause the eating disorder. And I think now we can pretty much definitively say the only thing they did was provide their genetic contributions."
Often times, Sim says, children and adolescents who develop eating disorders share certain characteristics, such as a high level of anxiety, a strong desire to avoid harm and danger, a fear of making mistakes and a drive for perfection.
"They do not like uncertainty. They like predictability. They like to structure what's going to happen in their day," Sim says. "This really can set the stage for utilizing food and controlling weight and shape because it adds a whole other layer of simplicity to their life. It's a road map for more certainty. For them, the ultimate threat is getting fat or gaining weight."
Still, Lutter and Sim say environmental factors do play a role in the development of these disorders. Between 50 percent and 70 percent of the risk of developing an eating disorder is genetic, and 30 percent to 50 percent of the risk is considered environmental, Lutter says.
"The most obvious environmental cause is the Western ideal of thinness and beauty," Lutter says. "In cultures in which thinness is prized, there are much higher rates of eating disorders."
Sim says the prevalence of dieting, particularly among women, can add to a person's predisposition and propel them into an eating disorder.
"It's been said that genes provide the kindling and dieting provides the fuel," Sim says. "People who might be vulnerable, who might have those genes, may never develop an eating disorder if they never go on a diet."
"Other times we see people dieting and never developing an eating disorder," Sim adds. "It speaks to genetics making these individuals vulnerable."
Lutter's study was published Tuesday in the Journal of Clinical Investigation.