twin studies

twin studies

This tag is associated with 6 posts

Demystifying the Genetic and Environmental Influences on Disordered Eating

Genetics play an important role in the development of eating disorders and disordered eating behaviours. To date, many (over 30!) twin studies have been done and all but two found significant genetic effects on the development of eating disorders and disordered eating. However, no methodology is without limitations and tentative conclusions become more convincing when the findings are confirmed using different experimental approaches.

Twin studies, while they offer many advantages, are not that good when it comes to detecting shared environmental effects on a particular trait (literally, evens that happen to both twins and affect them in the same way). Fortunately, twin studies are just one of several different ways that researchers can use to study heritability(A quick reminder: Heritability measures the amount of the variability in an observable trait/behaviour that can be attributed to genetic variation. This is NOT the same as stating that a particular fraction of an individual’s trait is caused by genetics.) 

Adoption studies (scroll to bottom of link) provide a powerful alternative method to assess heritability and they …

The Genetics of Thin-Ideal Internalization

The Tripartite Model of body image dissatisfaction postulates that three factors (peers, parents, and media) affect body image dissatisfaction and disordered eating through thin-ideal internalization and appearance comparison.

Thin-ideal internalization is the extent to which one accepts or “buys into” socioculturally defined beauty standards of thinness. The idea is that the more someone internalizes these standards, the more likely they are to engage in behaviours to achieve their “ideal”, and the more likely they are to develop an eating disorder.

A growing number of of studies have been done evaluating the validity of this model. Although I’m not well-read on the subject, it does seem like there is a growing number of studies showing an association between thin-ideal internalization and disordered eating practices.

But is the picture complete? Are peers, parents, and media the only or even the main factors that influence the extent of thin-ideal internalization?

One factor that’s curiously missing from the research is genetics. Can genetics play a role in explaining why some individuals are more prone to internalizing the …

Demystifying the Genetics of Eating Disorders – Part I

Today I thought I’d take the time to do an overview of what researchers know about the genetics of eating disorders and try to clear up some common misconceptions. The bulk of the content in this blog post comes from a very nice review paper published in 2011 by Drs. Stephanie Zerwas and Cynthia Bulik on the genetics and epigenetics of eating disorders. In an effort to keep blog posts short, this will be a multi-part mini-series.

When it comes to the genetics of eating disorders, there are two main questions that research ask: What is the relative contribution of genetic factors to eating disorder behaviours? And what are those genetic factors? I’ll talk about research attempting to answer the first question in this post and the second question in my next post.

In order to understand the role that genetics plays in influencing eating disorder behaviours, researchers use family, twin, and to a lesser extent, adoption studies.

FAMILY STUDIES

In family studies, researchers are typically asking What is the probability that a relative of someone with an eating disorder

Can Puberty Affect the Development of Eating Disorders?

Eating disorders typically begin in adolescence. One common explanation for this is that during adolescence females are increasingly exposed to the media, thin models, and dieting. While this is probably true to some extent, it doesn’t explain why the rates of eating disorders are quite low despite the high levels of exposure to thin models in the media. Out of 100 girls, only a handful develop eating disorders, yet all of them are exposed to the same magazines and TV shows.

This means there must be some other factors that differ between this group of girls. One hypothesis is that hormonal changes during puberty may modulate the genetic risk factors for eating disorders. These changes may “turn on” genes that predispose individuals to eating disorders. Previous research has shown that genetic factors modulate disordered eating (eating disorders have a high heritability), but how? What are the mechanisms of this modulation?

Exploring this idea, Dr. Kelly Klump and colleagues sought to focus on the role of estradiol–the predominant estrogen during reproductive years in females. Estradiol (and other hormones, …

How Common Are Eating Disorders? Incidence, Prevalence and Mortality Rates

Six month of blogging and I have yet to do a proper post on the prevalence of eating disorders. I think it is about time. I see all sorts of numbers thrown around, often depending on the purpose of the article and the author’s bias. Is it 1 in 1000, 1 in 100, 1 in 20 or maybe even 1 in 2? Who is right?

Well, it is a tricky question to answer.

The number depends on how the particular study was conducted. Here are some factors that may influence the final rates: the population being studied, the sample size, the definition of eating disorder, the methods used by researchers to identify and screen for individuals with eating disorders, the number of years over which data is collected, and so on. In other words, a lot! That’s why in order to get a better sense of the true numbers, I prefer to look at review articles summarizing several years worth of epidemiological studies.

For this post, I picked a relatively recent review, published in May 2012, by Smink, van …

The Genetics of Anorexia Nervosa

Is it the culture of thinness, obsession with dieting or just bad mothering? When it comes to determining the causes of anorexia nervosa, the answer appears to be none of the above. Increasingly, the evidence is pointing to genetics playing an important role in predisposing individuals to anorexia nervosa. Among clinicians and researchers, the notion that genetic factors are important in the development of anorexia nervosa seems uncontested. In this short review, Dr. Cynthia Bulik and colleagues summarize some of the findings in the genetics of anorexia nervosa.

Currently (DSM-IV), to be diagnosed with anorexia nervosa, a patient must show:

  • An inability to maintain normal weight (<85% of what is expected)
  • Intense fear of weight gain and/or becoming fat, though underweight
  • Obsession with body weight and shape, giving it undue importance in evaluating self-esteem/self-worth
  • Amenorrhea (missing 3 or more consecutive periods)
  • There are two AN-subtypes: restricting type (AN-R) and bingeing/purging type (AN-BP)

Bulik et al. outline some well-known personality characteristics and co-morbid psychiatric disorders commonly found in anorexia nervosa patients. AN patients tend to be perfectionists, exhibit a high …

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