Scientists may be closer to finding the genes that make a young person vulnerable to eating disorders.
Moreover, new techniques developed in the study may help researchers find genetic linkages for other complex medical conditions such as diabetes and high blood pressure.
Cynthia M. Bulik, PhD, director of the eating disorders program at the University of North Carolina at Chapel Hill, led the international team of eating-disorder researchers.
"The genetic research has helped us underscore that these are not simply social or cultural disorders — and they are not simply 'disorders of choice,'" Bulik tells WebMD. "When parents have a difficult time understanding why their daughter or son won't just eat more, it is helpful to provide them with evidence that there is a biological/genetic underpinning for this. We also tell them that genes alone do not cause these disorders."
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Six Essential Traits of Eating Disorders
Bulimia is an eating disorder in which a person goes on eating binges, and then purges by self-induced vomiting and/or laxative abuse. Bulimic patients typically maintain normal weight.
Anorexia is an eating disorder in which a person becomes extremely underweight by excessive dieting, excessive exercise, and/or purging.
Bulik and colleagues began by assembling a group of experts in bulimia and anorexia. Based on their clinical experience and knowledge of past research, the experts came up with a list of more than 100 behaviors and personality traits linked to these eating disorders.
"These are traits we see a lot in these folks, even after they recover from their eating disorders," Bulik says. "That is key, because we are looking for predisposing traits. We don't want traits caused by starvation."
They then boiled the list down to six traits that appear to run in families and thus might be influenced by inherited genes. Those traits are:
—Anxiety
—Obsessionality — thoughts that appear over and over again, or an intense preoccupation with symmetry, exactness, and order.
—Age at first menstruation. Girls who reach puberty earlier than others, Bulik says, become more full figured than their prepubescent peers. To fit in, they may wish to regain their childlike figure.
—Food-related obsessions
—Lowest body weight during eating disorder
—Concern over mistakes
Bulik and colleagues report their latest findings in the American Journal of Medical Genetics.
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Closing In on Bulimia Genes
Meanwhile, the researchers had been looking for families in which two or more members had an eating disorder. Some 400 people with anorexia or bulimia volunteered for the study. These volunteers underwent a battery of psychological tests. They also gave blood for genetic analysis.
Bulik and colleagues looked at whether people who shared any of the six traits of eating disorders also shared any genes or gene combinations. This is where they hit pay dirt.
Specific gene regions were linked to eating-disorder traits. These “signal peaks” were more pronounced for people with bulimia than for people with anorexia.
In a combined analysis, the anorexia signals dimmed the bulimia signals. This, the researchers suggest, probably means that anorexia and bulimia have different underlying genetic influences.
With these signals in hand, Bulik says, researchers now know where to look for bulimia genes.
"The human genome is a big place — some 30,000 genes," Bulik says. "We can now say, if you want the most bang for your buck, look here. So that is the next step. We will look at all the genes under those peaks, see what we know about what those genes do, and try to figure out if they play a role in anorexia or bulimia."
Genes Are Not Destiny
The Bulik study is important work, says eating-disorder expert Richard Kreipe, MD, chief of adolescent medicine at Children’s Hospital at Strong, University of Rochester, N.Y.
"We are going to be able to understand from [these] studies that there are certain traits individuals have that are probably linked to multiple genes coming together in different ways," Kreipe tells WebMD. "These genetic combinations may predispose a person to respond to environmental or developmental or other situations with the behaviors associated with eating disorders."
But Kreipe also warns that genetic influences are not destiny.
"Parents don't give children eating disorders by giving them their genes," Kreipe says. "If you have these genes, you are not doomed. The genes don't cause anorexia or bulimia. They may be associated with development and maintenance of eating disorders. Because of the behaviors people do reduce the negative consequences of these traits."
For example, people with a genetic predisposition for anxiety and bulimia may find that binge eating lessens their anxiety. That, Kreipe says, is a powerful motivation to binge eat. But it doesn't mean that there's nothing a person can do about it.
"The data are very clear that treatment can help," he says. "People with eating disorders can get better. They may still harbor these traits, but the traits don't need to be totally controlling the individual."
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By Daniel J. DeNoon, reviewed by Brunilda Nazario, MD
SOURCES: Bulik, C.M.American Journal of Medical Genetics Part B, published online, Sept. 8, 2005. Bacanu, S. American Journal of Medical Genetics Part B, published online, Sept. 8, 2005. Cynthia M. Bulik, PhD, director, UNC Eating Disorders Program, University of North Carolina, Chapel Hill.Richard Kreipe, MD,professor of pediatrics, University of Rochester; chief, division of adolescent medicine, Children’s Hospital at Strong, University of Rochester, N.Y.
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