A massive global study into the genetic origins of anorexia nervosa is suggesting this illness is not just a psychiatric condition but also a metabolic disorder. The research revealed metabolic genetic variants influencing fat burning, physical activity and other factors unique to those suffering from this chronic eating disorder, and not seen in other psychiatric conditions.

This large international study involved over 100 scientists around the world, tracking genetic data from nearly 17,000 subjects across 17 different countries. The research homed in on eight genetic variants that could be directly linked to anorexia nervosa.

Some of these gene variants unsurprisingly overlap with other psychiatric conditions, including depression, schizophrenia and obsessive-compulsive disorder, but not all the findings were as predictable. Several genetic variants uncovered correlated with metabolic processes including insulin resistance, leptin (an appetite-regulating hormone), and body mass index.

"Metabolic abnormalities seen in patients with anorexia nervosa are most often attributed to starvation, but our study shows metabolic differences may also contribute to the development of the disorder," says Gerome Breen, from King's College London, and co-lead on the new study. "Furthermore, our analyses indicate that the metabolic factors may play nearly or just as strong a role as purely psychiatric effects."

The physiological consequences of anorexia nervosa have traditionally been considered a result of the psychological features of the illness. This new study, however, suggests clinicians need to broaden their focus when dealing with anorexia patients.

"Until now, our focus has been on the psychological aspects of anorexia nervosa such as the patients' drive for thinness," says Cynthia Bulik, principle investigator on the new research. "Our findings strongly encourage us to also shine the torch on the role of metabolism to help understand why individuals with anorexia frequently drop back to dangerously low weights, even after therapeutic renourishment. A failure to consider the role of metabolism may have contributed to the poor track record among health professionals in treating this illness."

While this is the largest genetic study conducted to date focusing specifically on anorexia nervosa, the researchers do note this is just the tip of the iceberg in terms of uncovering the genetic origins of the illness. Hundreds of genes that play a role are most likely yet to be discovered and the researchers are looking to expand the reach of this study, recruiting more patients from around the world for future analysis.

"Our goal is to recruit 100,000 anorexia nervosa cases internationally with appropriate controls, and to also broaden our search beyond anorexia nervosa to include other eating disorders such as bulimia and binge eating disorder," explains Nicholas Martin, an Australian researcher working on the project, from QIMR Berghofer.

In the short term this research calls for anorexia nervosa to be reconsidered as a "metabo-psychiatric disorder". This means clinicians should not just focus on the psychiatric component of the illness when developing treatments, but also consider the metabolic factors that seem to be at play.

"This is ground-breaking research that significantly increases our understanding of the genetic origins of this serious illness," says Andrew Radford, from UK-based eating disorder charity, Beat. "We strongly encourage researchers to examine the results of this study and consider how it can contribute to the development of new treatments so we can end the pain and suffering of eating disorders."

The new study was published in the journal Nature Genetics.