Anorexia nervosa is a heritable psychiatric disorder with warning signs that can be identified decades before the onset of the illness, the largest twin study on the disorder shows.
“Genes play a substantial role in the development of this illness; there is a clear biological component,” said lead author Cynthia M. Bulik, Ph.D., in a teleconference about the new research (Arch. Gen. Psychiatry 2006;63:305–12).
The findings are good news for patients and their families, said Dr. Bulik, the William R. and Jeanne H. Jordan Distinguished Professor of Eating Disorders at the University of North Carolina, Chapel Hill.
“We have gone through too much time where parents have been blamed. Now families and patients can be liberated and empowered,” Dr. Bulik said. “This helps them understand they are fighting their biology.”
The study included 31,406 twins from the Swedish Twin Registry. The twins, born during 1935–1958, were sent a questionnaire in 1973 that assessed demographics, physical illnesses, physical activity level, personality, stress, and work exposures. Seven potential predictors of the development of anorexia nervosa (AN) were evaluated in the questionnaire, including body mass index, gastric problems, excessive exercise, perceived life stress, neuroticism, and extraversion. Zygosity information also was obtained.
The subjects were then interviewed in 1998–2002 at a median age of 54.6 years to establish who had gone on to develop AN, and to determine the predictors.
The study found that 1.2% of the females and 0.29% of the males met diagnostic criteria for a lifetime history of AN, a prevalence in line with other studies of the disorder. However, when the cohort was divided into those born in 1944 or earlier, and those born in 1945 or later, there was evidence of an increasing prevalence in women (0.65% prevalence in the older female cohort, compared with 1.56% in the younger group). Prevalence rates did not change for men.
Examining the incidence of AN as it related to zygosity, the researchers found a much higher concordance rate for AN among monozygotic twins than among dizygotic twins–signaling a clear genetic component, Dr. Bulik said. The analysis revealed that genetics accounted for 56% of an individual's risk of developing the disorder, unique environment accounted for 38%, and shared environment accounted for 5%.
This information is promising in the search for targeted prevention and medical treatments for AN, she said. “Research like this shows [AN] is not a sociocultural disorder. We need to look elsewhere. We need to look at genes.” She said other work in this field has identified several genes on chromosome 1 that might be involved in the development of AN and could be medication targets.
“I am perplexed and disappointed that we don't have medication for AN, and this is in part because we have not yet explained the biology adequately,” she said.
The study also found that of the potential predictors of AN assessed in the 1973 questionnaire, only neuroticism was predictive of the development of the disorder. The finding is notable because there have been few “truly prospective” risk-factor studies of AN, Dr. Bulik noted in the study. “What remains unknown is whether neuroticism is a nonspecific predictor of the development of psychopathology in general or whether it is specifically predictive of the emergence of AN.”
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