By LEE BOWMAN
Scripps Howard News Service
March 06, 2006
The study also pinpointed "neuroticism" - a tendency to be anxious and depressed - earlier in life as a significant factor linked to later development of the eating disorder.
Anorexia is a psychiatric illness characterized by a person's refusal to maintain a minimal healthy body weight, intense fear of weight gain and a distorted body image. It occurs mainly among females in adolescence and young adulthood. It's estimated that up to 1 percent of females have anorexia, and the condition is estimated to be fatal to as many as 15 percent of those diagnosed with it.
While the notion that genes play a role in the disorder has been suggested by several previous studies - and several researchers already have identified specific genes that appear to contribute to the risk - the study published Monday in the Archives of General Psychiatry is the first to calculate the liability from genetics.
Specifically, it assigns 56 percent of the risk from genes, the remainder from environmental factors.
"Family studies show that if you have a family member who has an eating disorder, you're between seven and 12 times at greater risk for developing an eating disorder yourself,'' said Cynthia Bulik, a specialist on eating disorders at the University of North Carolina School of Medicine and lead author of the new study.
But just because something runs in a family doesn't distinguish whether the condition caused by genetics or the psychosocial environment within that family. And several earlier twin studies that included as many as 4,000 pairs didn't have sufficient statistical power to accurately plot the genetic risk.
"Our study shows a very clear and substantial biological component to anorexia nervosa, and my hope is that this will offer some support to patients and their families,'' Bulik said.
"For far too long, people suffering from this disorder have had to deal with the theory that this is all societal, that somehow they choose to have anorexia, or parents have had to deal with the blame placed on them because somehow their parenting style caused this,'' Bulik said. "Now, they know that they really need to go against the tide of their biology to overcome this."
Working with colleagues at the Karolinska Institute in Stockholm, Bulik's team worked with a sample of 31,406 twins born between 1935 and 1958. About half the sample was identical twin pairs who are genetically identical, the other half were fraternal twins who are no more genetically similar than siblings who are not twins.
During a four-year follow-up period that ended in 2002, the twins were screened for a range of disorders, including anorexia.
The overall prevalence of anorexia in 2002 was 1.2 percent among women and .29 percent for men, with the disorder more likely to be shared between identical than fraternal twins. Those born after 1945 also had a higher prevalence of anorexia than those born earlier.
"Of course, the gene pool didn't change. The environment has indeed changed and cultural pressure to be thin has been greater on the younger part of the study group,'' Bulik said.
Knowledge that genes play so much of a role should allow researchers to begin focusing on why some young people are more sensitive to environmental pressures to be thin by not eating, and to narrow the search for specific genes that influence eating and body image.
Using information from questionnaires filled out in the early 70s, the researchers also found that neuroticism is a predictor of anorexia. The tendency to be depressed and anxious and emotionally instable, along with the any family history of eating disorders, could help family doctors and other health care providers identify young patients at high risk for the eating disorder, Bulik said.
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