Evidence that the association of childhood trauma with psychosis and related psychopathology is not explained by gene-environment correlation: A monozygotic twin differences approach

Background: Converging evidence supports childhood trauma as possible causal risk for psychosis and related psychopathology. However, studies have shown that baseline psychotic symptoms may actually increase risk for subsequent victimization, suggesting that exposure to CT is not random but may result from pre-existing vulnerability. Therefore, studies testing whether the association between CT and psychopathology persists when accounting for gene-environment correlation are much needed. Methods: A monozygotic (MZ) twin differences approach was used to examine whether differences in CT exposure among MZ twin pairs would be associated with MZ differences in symptoms. As MZ twins are genetically identical, within-pair correlations between CT exposure and psychopathology rule out the possibility that the association is solely attributable to gene-environment correlation. 266 monozygotic twins (133 pairs) from a larger general population study were available for analysis. Results: CT was associated with symptoms of psychosis (B = 0.62; SE = 0.08, p <.001) and overall psychopathology (B = 43.13; SE = 6.27; p <.001). There were measurable differences within pairs in CT exposure and symptoms, allowing for meaningful within-pair differences. Within-pair differences in CT exposure were associated with within-pair differences in symptoms of psychosis (B = 0.35; SE = 0.16; p =.024), as well as with overall psychopathology (B = 29.22; SE = 12.24; p =.018), anxiety (B = 0.65; SE = 0.21; p =.002) and depression (B = 0.37; SE = 0.18; p =.043). Conclusion: While it is not unlikely that pre-existing vulnerability may increase the risk for traumatic exposures, such gene-environment correlation does not explain away the association between CT and psychopathology. The present findings thus suggest that at least part of the association between CT and psychopathology may be causal.