The Genetics Behind Eating Disorders
In today’s social media-governed society, it seems like almost everyone is preoccupied with their body and diet. It’s no surprise that eating disorders and disordered eating run rampant in modern-day society. But how much of this issue is a social issue, and how much of eating disorders is attributed to genetics? Research has shown that the pathology of eating disorders may be influenced by genes.
There are various existing research papers that study the genetics behind various types of eating disorders, with anorexia nervosa (AN), bulimia nervosa (BN) and binge-eating disorder (BED) being a few examples. AN, which is the most well-studied eating disorder, is characterized by an extreme fear of weight gain and dangerously low body weight, and sufferers engage in a variety of behaviors like fasting and excessive exercise that contribute to a negative energy balance. Bulimia nervosa (BN) and binge-eating disorder (BED) are characterized by the consumption of large amounts of food in a short period of time due to a sense of loss of control, and those with bulimia nervosa engage in compensatory behaviors like vomiting and laxative abuse to counteract the effects of binge eating. Previous association studies have demonstrated correlations between genes and eating disorder onset. Family studies have generally discovered the clustering of eating disorders in families of individuals with AN and BN, which supports the hypothesis of familial transmission of both disorders, , , . However, environmental and genetic factors may also be involved, which is why twin studies on eating disorders are generally more reliable. Twin studies compare identical twins, who share the same set of genes, and fraternal twins, who share approximately the same amount of genes as regular siblings, which allows for better genetic studies that eliminate environmental factors as a confounding factor. Various studies have generally discovered a great similarity in AN and BN in identical twins compared to fraternal twins, , ,  and consistent findings tend to support moderate heritability of eating disorder traits. Another twin study by Munn-Chernoff and colleagues discovered a correlation between ADHD and binge eating. Since twin studies more effectively rule out environmental influences on the onset of eating disorders, the findings of these studies seem to indicate a prevalent role of genes in the development of an eating disorder. Further association studies have correlated comorbidities like depression, anxiety, personality and physical characteristics with an increased risk of AN and BN. Since these comorbidities often run in families, these findings may indicate a shared genetic effect of eating disorders within families as well.
Molecular genetic studies have also demonstrated potential for the relationship between genetics and eating disorders. The findings from association studies, such as the correlation between AN and BN with monoamine functioning that is related to serotonin and dopamine-related genes, may be more prone to biases in the outcome due to confounding factors. Additional studies are needed to clarify conflicting findings and replicate initial results, especially for BN, which is not studied as extensively as AN. Linkage studies, with enough multiplex pedigrees or extreme sibling pairs, can analyze anonymous genetic markers scattered across the genome to identify chromosomal regions that might contain genes that contribute to certain disorders. Berrettini and colleagues have done allele-sharing linkage analyses to identify genes contributing to eating disorders in 196 families with 2 or more family members with AN, BN or eating disorders not otherwise specified (EDNOS). Initial analyses showed only modest results, like due to the sheer number of loci involved in the onset of these disorders and the fact that three eating disorders were being tested. More homogenous phenotypes and larger numbers of subjects would likely improve the ability to identify genetic effects.
Besides studying the direct effects of genes on the onset of eating disorders, researchers have delved into the subject area of epigenetics. Epigenetics refers to the various biochemical mechanisms that may regulate genes, meaning that environmental exposures can influence how genes are expressed. DNA methylation is one of the most widely studied epigenetic mechanisms in the context of complex traits. A systematic review by Hubel et al, 2019 analyzed 17 studies of the epigenetics of eating disorders, and the conclusions were not all that significant. The four studies studying the effect of DNA methylation on eating disorder onset reported conflicting or inconclusive results, , , . Candidate gene studies, which are hypothesis-driven and investigations on DNA methylation in the vicinity of selected genes, were overall low quality with extremely small sample sizes. Epigenome-wide association studies (EWAS) also didn’t seem to display extremely conclusive results. As of right now, it seems that further studies must be conducted to correlate epigenetic mechanisms with eating disorder onset.
Research on the role of genetics in eating disorder pathology is still underway. Although there have been many research studies on this relationship, more linkage studies and studies with large population samples need to be conducted to solidify the relationship between genetics and eating disorders. With more research on how genetics contributes to the development of a common but distressing mental illness, researchers can better understand how to target certain biological pathways that have been affected by gene mutations and develop more effective drug therapies.
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