Genetic and environmental components to self-induced vomiting

Abstract

Objective: We examined the association between the genetic and environmental factors contributing to the liability to having ever engaged in self-induced vomiting (SIV initiation) and the genetic and environmental factors contributing to regular SIV behaviors (weekly or daily) for weight control.

Method: SIV was assessed in 3,942 women from monozygotic twin pairs and 2,790 women from same-sex dizygotic twin pairs, aged 20-47, from the Swedish Twin study of Adults: Genes and Environment. A causal-contingent-common pathway model assessed the extent to which genetic and environmental factors that influence initiation of SIV also influence regular SIV behaviors.

Results: In the best-fit model, genetic and individual-specific environmental factors influenced liability to SIV initiation. The genetic factors influencing regular SIV behaviors were the same as the genetic factors influencing SIV initiation. Additional individual-specific environmental factors that were unrelated to SIV initiation influenced regular SIV behaviors.

Discussion: Our findings provide evidence that the underlying liabilities for SIV initiation and regular SIV lie on the same continuum given the degree of overlap in risk between SIV initiation and regular SIV behaviors. Further, the lack of specific genetic factors and the importance of individual-specific environmental factors for regular SIV behaviors highlight the significance of environmental factors in the etiology of eating disorder symptomatology and the non-deterministic nature of genetic factors. Finally, our results suggest that when it comes to preventing individuals from developing regular SIV behavior, intervening at an environmental level is warranted.

Keywords: bulimia nervosa; eating disorder; heritability; purging disorder; self-induced vomiting; twin study.

Figure 1. Causal-contingent-common pathway model

Note. SIV = self-induced vomiting. Genetic (A or a), shared environmental (C or c), and individual-specific environmental (E or e) factors are presented for the two stages of SIV. The subscript “I” (or “I”) refers to initiation of (SIV), whereas the subscript “P” (or “p”) refers to progression of SIV. The path coefficient “b” represents the pathway from initiation to progression of SIV.