Overlap between anorexia and bulimia nervosa: understanding genetic and environmental effects using a population registry in Sweden

Background: Symptomatic flux and familial co-aggregation of anorexia nervosa and bulimia nervosa suggests etiological overlap between these eating disorders. One previous twin study based on self-ratings explored the genetic... [ view full abstract ]

Background: Symptomatic flux and familial co-aggregation of anorexia nervosa and bulimia nervosa suggests etiological overlap between these eating disorders. One previous twin study based on self-ratings explored the genetic and environmental aspects of the overlap on the symptom level.¹ No previous study has explored the relative contribution of genetic and environmental influences on clinically diagnosed anorexia and bulimia nervosa.

Method: We applied bi-variate structural equation modeling on full-sisters (334,433 pairs) and maternal half-sisters (57,036 pairs) that were randomly selected from the Swedish female population born 1970-2005. Anorexia nervosa included registered clinically diagnosed typical and atypical anorexia nervosa, and bulimia nervosa included registered clinically diagnosed typical and atypical bulimia nervosa.

Results: In the study sample, heritability was estimated as .44 for anorexia nervosa (95% confidence interval [CI]=.38-.51) and .34 for bulimia nervosa (95% CI=.25-.44). Nonshared environmental effects explained the remaining phenotypic variance (anorexia nervosa .56, 95% CI=.49-.62; bulimia nervosa .66, 95% CI=.56-.75). The phenotypic correlation between the two disorders was estimated as .59. The cross-sister-cross-disorder correlation was significantly higher in full-sisters (.16, sd.=.0019) than in maternal half-sisters (.022, sd.= .052). Around half of the phenotypic covariance between anorexia and bulimia nervosa was attributable to genetic influences (.52, 95% CI=.41-.63). We observed statistically significant genetic (.79, 95% CI=.63-.95) and environmental (.47, 95% CI=.37-1.00) correlations between these disorders.

Conclusion: In line with the only previous twin study based on self-ratings, we report a moderate-to-high genetic correlation and a moderate environmental correlation between anorexia and bulimia nervosa.¹ This points towards a shared mechanism that could guide future molecular genetic research and further encourage clinicians to be vigilant for symptom flux in patients with these eating disorders.

Reference:

1          Bulik, C. M. et al. Understanding the relation between anorexia nervosa and bulimia nervosa in a Swedish national twin sample. Biol Psychiatry 67, 71-77, doi:10.1016/j.biopsych.2009.08.010 (2010).