Childhood maltreatment is a robust predictor of aggression. Research indicates that both maltreatment experiences and aggression are moderately heritable. It has been hypothesized that gene–environment correlation may be at play, whereby genetic predispositions to aggression in parents and children may be confounded with family environments conducive to its expression. Building on this framework, we tested whether maltreatment mediates the association between a polygenic score for aggression (PGSAGG) and school-age aggression, and whether this varied for reactive and proactive aggression.

The sample comprised 721 participants (44.9% males; 99.0% White) with prospective assessments of maltreatment from 5 months to 12 years (10 assessments;1998–2010), and teachers-reported aggression from ages 6 to 13 (6 assessments; 2004–2011). The PGSAGG was derived using a Bayesian estimation method (PRS-CS).

PGSAGG was associated with most aggression measures across specific ages and trajectories. Maltreatment experiences partially mediated the association between PGSAGG and the Childhood-Limited trajectory of reactive – but not proactive – aggression.

Children with higher genetic propensities for aggression were more likely to experience maltreatment, which partly explained the association between PGSAGG and a Childhood-Limited trajectory of reactive aggression during elementary school. This finding reinforces the possibility of confounding influences between genetic liability for aggression and maltreatment experiences.