For National Eating Disorder Awareness Week 2018, Tonic is taking a look at our relationship with food—and how what we eat is often symbolic of who we are . Our intention is to shed light on the ways in which eating disorders have persevered, even during an era known for #bodypositivity, and to share the stories that are often overlooked.
In an 1873 paper, English physician Sir William Gull described three cases of women who appeared extremely emaciated but had no other abnormal symptoms. But despite their physical frailty, they all exhibited restlessness and excessive physical activity. Gull named the condition “anorexia nervosa” and blamed the patients' “morbid mental state.” He recommended a treatment “fitted for persons of unsound mind,” i.e. force-feeding them at regular intervals.
While our knowledge and treatment of eating disorders has come a long way, researchers still can’t say the exact causes of the conditions. Environmental factors certainly contribute, such as a the societal pressure to be thin in modern Western culture, which has been identified as a specific risk factor for eating disorders. Also, interventions that reduce thin-ideal internalization have been associated with reductions in eating disorder symptoms.
But a growing number of studies are finding that genetic factors may be a major factor at play. In other words, eating disorders can run in the family similar to diabetes and heart disease.
Initially, researchers discovered through studies of patients and their relatives that eating disorders tend to aggregate in certain families more than others. Several twin studies also estimated a significant heritability for anorexia nervosa, bulimia nervosa, and binge-eating disorder.
Today, with the advances in genome sequencing technology and cost, the focus has shifted to hunting for individual genes possibly linked to greater eating disorder risk. Last year, scientists pinpointed the first genome-wide significant marker for anorexia nervosa in an area that harbors genes associated with type 1 diabetes and other autoimmune disorders.
The growing body of research supports the idea that eating disorders are partly biological illnesses that might require new treatment options, rather purely caused by societal influences.
“The genetic component is estimated to account for 50 to 70 percent of the risk of developing an eating disorder, which is fairly substantial, making it one of the most heritable psychiatric disorders,” said Michael Lutter, a psychiatrist at the Eating Recovery Center in Dallas. “If you have a first-degree female relative with an eating disorder, you are about ten times more likely to have an eating disorder in your life.”
Even though heritability has been observed in lots of families, it’s a hard disorder to trace, or to know for sure if other members have had it.
“We often see 'sporadic' cases. However, given the stigma associated with eating disorders, we really cannot be confident that other family members have not had an eating disorder,” said Cynthia Bulik, Founding Director of the UNC Center of Excellence for Eating Disorders. “Especially among older generations, we hear things like ‘Aunt Louise ate like a bird,”’ or ‘My mother had body image issues all of her life’—but they may never have received a formal diagnosis of an eating disorder.”
A common tool in determining heritability is a twin study, which looks at certain traits in twins raised in the same family environment. A researcher compares the similarity of a trait between sets of identical twins, who share all their DNA, to the similarity between sets of fraternal twins, who only share about half their DNA. Any additional likeness found in the identical twins is chalked up to genes instead of upbringing.
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These studies estimate the genetic component of anorexia nervosa to be around 48 to 74 percent, while that of bulimia ranges from 55 to 62 percent. Less research has been done on the heritability of binge-eating disorder, but current estimates hover at 39 to 45 percent.
More recently, researchers have been sequencing the genomes of those with eating disorders to find the exact genetic variants that contribute. These genome-wide association studies search for small variations, that occur more frequently in people with a certain disease.
In 2014, a study by the Eating Disorders Working Group of the Psychiatric Genomics Consortium (PGC-ED) identified the first genetic marker for anorexia nervosa. By comparing the DNA of 3,495 anorexia nervosa cases and 10,982 controls, the researchers found a variation associated with the disease on chromosome 12 in an area previously associated with type 1 diabetes and autoimmune disorders.
They also looked for genetic correlations, which asks whether two disorders or traits are caused by the same genes. Both neuroticism and schizophrenia had a high genetic correlation—as in, shared many of the same types of gene variants—with anorexia. This connection isn’t surprising and supports the idea that eating disorders are a kind of psychiatric disease with an overlapping genetic risk.
But the study also found genetic ties to metabolic features—in particular, negative correlations between anorexia and extremely high body mass index (BMI), obesity, and normal BMI. A negative genetic correlation indicates that the same genetic variants that increase one trait’s risk decrease the other’s, and vice versa. The PGC-ED is currently working on genome-wide association studies of bulimia nervosa and binge-eating disorder.
“This finding brings us into new territory and suggests that we might need to start thinking about anorexia nervosa as both a psychiatric and a metabolic illness,” said PGC-ED researcher Bulik.
But as with depression and schizophrenia, eating disorders are complex genetic illnesses—we’ll never find a single “bulimia gene” that we can inherit from our parents. Instead, there are probably tens of thousands of variants that combine to create one's overall genetic risk of disease.
“On one end of the spectrum, there are rare variants that give a very high risk of developing an eating disorder, like maybe 60 to 70 percent,” said Lutter. “On the other end of the spectrum are fairly common variants that each give a very small increase in the risk of developing an eating disorder, like 0.1 percent.”
Lutter focuses on those rare mutations that account for a relatively small proportion of eating disorder cases but confer high risk. Studying these genes, similar to BRCA1 and BRCA2 in breast cancer, can help give insight into the biology of these illnesses. For instance, Lutter and his colleagues discovered in 2013 that people with mutations in two genes—ESRRA and HDAC4—have a 90 percent and 85 percent chance of developing an eating disorder, respectively.
His lab also found a set of 245 genes more likely to be mutated in patients with binge-eating behaviors. These mutations affect neuropeptides—molecules used by neurons for communication—that control appetite and food intake, making people more likely to binge. Another set of 186 genes involved in inflammation tend to appear more often in patients with anorexia nervosa restricting-type behaviors.
Based on these findings, Lutter hopes to cluster patients into these two groups and target more effective treatments. In the study, he tested the therapeutic effects of targeting the neuropeptide pathway with a drug in a binge-eating mouse model. The animals significantly reduced their food intake during binge episodes after taking a low dose of the drug, which falls into the same class of medications already FDA approved for diabetes and weight management.
Aside from developing new targeted medications, studying the genomes of those with eating disorders can help researchers answer some lingering questions about the disease. For instance, why some individuals are more vulnerable to environmental risk factors like dieting, while others can diet without a problem.
“We know that some adolescents, for example, can go on a diet with no long term adverse effects at all. They go off the diet and there are no changes to their eating habits, metabolism, or psychology,” said Bulik. “For others, however, that first diet can be a very high risk event that accelerates a descent into anorexia nervosa. Genetic research may hold the answer to the individual differences that make people differentially vulnerable to such environmental insults, and thereby help with illness prevention.”
As genome sequencing technology continues to improve, more information will continue to be uncovered about the true origins of eating disorders—and hopefully, better treatment options will follow. Instead of being dismissed as a “morbid mental state” or a teenage girl problem, rigorous genetic research has helped eating disorders become increasingly recognized as a biological illness that affect people of all backgrounds.
If you or someone you know is dealing with an eating disorder, contact the helpline of the National Eating Disorders Association (NEDA) at 1-800-931-2237, or visit their site. You can also live chat with a volunteer via Facebook Messenger, and text 'NED!' to 741741 for crisis support 24/7.
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