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Unpredictability in the child's environment has recently emerged as a significant and unique form of early life adversity (ELA). Cross-sectional studies have linked childhood unpredictability with increased post-traumatic stress disorder (PTSD) symptoms in adults; however, no prospective studies have tested the link between childhood unpredictability and PTSD risk in later life, nor what processes, such as increased anhedonia symptoms, might mediate such risk. Here, we leveraged three distinct prospective, longitudinal cohorts to test the hypothesis that unpredictability during childhood contributes to adult PTSD via worsening anhedonia symptoms.

Participants were male service members (n=314), adult females (n=170), and adolescents (n=137) recruited for separate longitudinal investigations. All completed dimensional assessments of anhedonia symptoms and PTSD; childhood trauma and childhood unpredictability were measured by the Questionnaire for Unpredictability in Childhood (QUIC). Pearson correlations tested relations between QUIC, anhedonia symptoms, and PTSD symptoms. Mediational models tested whether the link between childhood unpredictability and PTSD is mediated by increased anhedonia symptoms by estimating indirect effects via bootstrapped path analysis.

Childhood unpredictability was associated with increased adult PTSD symptoms in all three cohorts (rs>.19, ps<.016). Further, in all three cohorts, the relationship was partially mediated by higher anhedonia symptoms (bs>0.046, 95% confidence intervals = 0.01-0.12). All effects remained significant when controlling for levels of childhood trauma and removing anhedonia-related PTSD items.

Unpredictability during childhood may confer risk for adult PTSD, and this increased risk may occur via alterations in anhedonia symptoms. Efforts to increase predictability during childhood could enhance resilience to later traumatic events.