The Ties That Bind: Co-Twin Influences on Psychopathology in a Sample of Twins

Research has begun to better describe twinship and twin identity development, the potential advantages and disadvantages of twinship, and factors related to twins’ shared psychological symptomatology. Research also supports the concept of emotional contagion, in which one person’s emotional state can be transmitted to another person. This phenomenon may be more common among twins due to factors such as closeness, dependence, and general similarity. The current study proposed a series of regression models to investigate how predictive pathways toward anxiety among a sample of twins could be impacted by the psychological traits and functioning of their co-twins. The current sample included same-sex twins born in three different birth cohorts with data collected over a five-year timeframe as part of the larger Twinlife study. Results revealed a statistically significant predictive relationship between twin anxiety and co-twin anxiety three years later, particularly among monozygotic males and older twins. There was also a predictive relationship between twin external locus of control and co-twin anxiety five years later among dizygotic twins. On pathways between one twin’s frequency of stressful life events and future anxiety, there was no evidence of a mediating role of co-twin external locus of control or moderating role of co-twin coping style. These findings provide a glimpse into the dynamic and reciprocal nature of twins’ behavioral health outcomes while raising additional questions about twin study design, informing clinical approaches to anxiety treatment in twins, and laying the groundwork for continued exploration of psychological health and outcomes within the context of twinship.