Zygosity and autonomic stress reactivity during social exclusion: biofeedback findings from the TwinCord-EDID study.

Objective: Patients with functional gastrointestinal disorders (FGID) and/or eating disorders (ED) often report increased sensitivity to psychosocial stress. This exploratory study examined autonomic responses, measured via heart rate variability (HRV) and biofeedback, to experimentally induced social exclusion (Cyberball task) in monozygotic and dizygotic twins with and without questionnaire-based symptoms symptoms for FGID and ED. The twin design was used to explore potential genetic and environmental contributions to stress reactivity. Methods: 35 monozygotic and dizygotic twin pairs participated. Zygosity was determined via genetic blood testing. Participants were assigned to four groups based on questionnaire data assessing symptoms for ED and/or FGID: (I) ED-related symptoms, (II) FGID-related symptoms, (III) combined symptoms, and (VI) asymptomatic controls. All participants completed a controlled social exclusion task using the Cyberball paradigm. Heart rate variability (HRV), skin conductance (SC), skin temperature (ST) and subjective stress ratings (VAS) were assessed during baseline, exclusion and recovery phases. Analyses focused on exploratory group comparisons as well as twin-based concordance, intraclass correlations and Falconer estimates. The study was approved by the Ethics Commission at the Medical Faculty of Eberhard-Karls-Universität and at Tübingen University Hospital (project number 094/2022B01). All subjects gave written informed consent. Results: Across the total sample, SC, ST, HRV, and VAS significantly changed across experimental phases, confirming successful stress induction and recovery. No significant differences emerged between symptom groups. Exploratory analyses revealed zygosity-related interactions for selected HRV indices and birth-order effects in VAS. Twin-based analyses suggested that non-shared environmental factors may contribute substantially to variability in physiological stress response, whereas possible genetic influences were observed for subjective stress ratings and selected HRV indices. However, these findings should be interpreted cautiously given the limited sample size and exploratory nature of the analyses. Conclusion: Social exclusion induced clear autonomic and subjective stress responses across all participants, independent of symptom status. While no group differences were observed, exploratory twin analyses provide preliminary indications that both environmental and genetic factors may contribute to individual differences in stress reactivity. Dute to the sample size and the exploratory design, these findings should be regarded as hypotheses-generating and require replication in larger twin cohorts.