A Shared Genetic Propensity Underlies Experiences of Bullying Victimization in Late Childhood and Self-Rated Paranoid Thinking in Adolescence

Background: Bullying is a risk factor for developing psychotic experiences (PEs). Whether bullying is associated with particular PEs, and the extent to which genes and environments influence the association, are unknown. This study investigated which specific PEs in adolescence are associated with earlier bullying victimization and the genetic and environmental contributions underlying their association. Method: Participants were 4826 twin pairs from a longitudinal community-based twin study in England and Wales who reported on their bullying victimization at the age of 12 years. Measures of specific PEs (self-rated Paranoia, Hallucinations, Cognitive disorganization, Grandiosity, Anhedonia, and parent-rated Negative Symptoms) were recorded at age of 16 years. Results: Childhood bullying victimization was most strongly associated with Paranoia in adolescence (r = .26; P < .01), with weaker associations with Hallucinations, Cognitive Disorganization, parent-rated Negative Symptoms (r = .12-.20; P < .01), Grandiosity (r = .04; P < .05), and Anhedonia (r = .00, n.s.). Bivariate twin model-fitting demonstrated that bullying victimization and Paranoia were both heritable (35% and 52%, respectively) with unique environmental influences (39% and 48%, respectively), and bullying victimization showed common environmental influences (26%). The association between bullying victimization and Paranoia operated almost entirely via genetic influences (bivariate heritability = 93%), with considerable genetic overlap (genetic correlation = .55). Conclusion: In contrast to the assumed role of bullying victimization as an environmental trigger, these data suggest that bullying victimization in late childhood is particularly linked to self-rated Paranoia in adolescence via a shared genetic propensity. Clinically, individuals with a history of bullying victimization are predicted to be particularly susceptible to paranoid symptoms.