For the first time, scientists have identified a set of specific gene variants linked to anorexia nervosa, providing some of the strongest evidence yet that the eating disorder is not purely a psychiatric illness.
In a massive, six-year-long investigation involving researchers from over 100 institutions worldwide, scientists discovered eight genetic markers significantly associated with the condition, some of which suggest its origins are also tied to metabolism.
Previous research by some of the same team had already laid the groundwork for the new findings, identifying in 2017 the first genetic locus correlated with the condition, based on an analysis of approximately 3,500 anorexia cases and almost 11,000 controls.
Now, the scientist who led that effort, clinical psychologist Cynthia Bulik from the University of North Carolina, is back with an even broader genome-wide association study, and the implications could make us rethink a lot of the current assumptions about anorexia nervosa.
"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 one of the team, psychiatric geneticist Gerome Breen from King's College London.
"Furthermore, our analyses indicate that the metabolic factors may play nearly or just as strong a role as purely psychiatric effects."
In the study, the researchers analysed the DNA of 16,992 patients with anorexia nervosa and compared it with the genetic information of 55,525 people without the condition, looking for genetic variants that could be associated with the disease, which has long been identified as having the highest mortality rate of any mental disorder.
For such a serious illness, it's one we still have a long way to go in terms of adequately treating, in part because the causes have never been well understood – and while therapy can help and medications can ease some associated symptoms, there's no guaranteed cure for every single person, and relapses remain common.
Thankfully, it looks like we just made some progress, after the researchers analysed over 70,000 genomes and found something quite unpredicted.
"What we expected was to find genes that are clearly implicated in the psychiatric mental and health aspects of the disease, which is obviously important," genetic epidemiologist Nicholas Martin from the QIMR Berghofer Medical Research Institute in Australia told ABC News.
"But what has taken us by surprise is finding that there seem to be very strong links with metabolism as well."
In all, the team identified eight genetic variants associated with anorexia. Some of these overlapped with psychiatric disorders such as obsessive-compulsive disorder, depression, anxiety, and schizophrenia, but there was also a link to metabolic function, such as people's ability to metabolise fats and sugars.
While the nature of this link between metabolic functions and anorexia isn't yet understood, the findings suggest metabolic issues could produce a biological predisposition to the condition that previously researchers hadn't fully comprehended.
"We cautiously note that these results represent the first indications of specific pathways, tissues, and cell types that may mediate genetic risk for anorexia nervosa," the authors write in their paper.
"Fundamental metabolic dysregulation may contribute to the exceptional difficulty that individuals with anorexia nervosa have in maintaining a healthy BMI (even after therapeutic renourishment)."
There's still a lot more to uncover here about what these associations actually signify, and there are other limitations with how much we can conclude from observational studies – particularly in this study, where the participants came from primarily European backgrounds, meaning the results are yet to be replicated across other ethnicities and cultures.
Nonetheless, the researchers say the findings give us fresh leads for investigating potential causes of anorexia, and hopefully new paths towards improved treatment.
"We've got the first eight genes, but we know there are hundreds more genes to find, and we can only do that by broadening the study and recruiting more participants," Martin said in a press release.
"By showing the role genetics plays in anorexia nervosa we should be able to remove any remaining stigma associated with the condition for patients and their families."
The findings are reported in Nature Genetics.