Preliminary Evidence That Shared Genetic Influences Underlie Comorbidity Between Self-Reported Eating and Internalizing Disorders and Gastrointestinal Disease in Adult Women and Men.

Introduction: Accumulating research suggests both eating disorders (EDs) and internalizing disorders (e.g., anxiety, depression) are associated with gastrointestinal disease (e.g., irritable bowel syndrome, inflammatory bowel disease). However, the mechanisms underlying comorbidity with gastrointestinal disease-and whether they may differ for eating and internalizing disorders-remain poorly understood. Addressing these gaps is a critical first step to refining etiologic models of comorbidity and identifying potential targets for intervention.

Method: Participants included female and male twins ages 18-65 from the population-based MSU Twin Registry (N = 5883). Lifetime history of EDs, internalizing disorders, and gastrointestinal disease was assessed via questionnaire. We first examined whether EDs and internalizing disorders were independently associated with gastrointestinal disease phenotypically. We then used trivariate Cholesky decomposition twin models to investigate whether EDs and internalizing disorders were related to gastrointestinal disease through overlapping or distinct genetic/environmental pathways.

Results: Eating (OR = 2.54, p = 0.009) and internalizing (OR = 2.14, p < 0.001) disorders were independently associated with gastrointestinal disease. Conclusions were unchanged after adjusting for important covariates (e.g., body mass index, age) and did not significantly differ across sex. Twin models suggested genetic influences shared by all three conditions explained their co-occurrence, with 31% of the variance in EDs and 12% of the variance in gastrointestinal disease attributable to genetic influences shared with internalizing disorders.

Conclusion: Shared genetic mechanisms may contribute to comorbidity between EDs, internalizing disorders, and gastrointestinal disease. Identifying overlapping molecular pathways could potentially lead to novel interventions that simultaneously address all three conditions.