Independent Contributions of Callous-Unemotional Behaviors and Quantitative Autistic Traits to Aggression in Early Childhood

Objective: Callous-unemotional (CU) behaviors and quantitative autistic traits (QATs), heritable domains implicated in social development, are both associated with reduced prosocial behavior and increased aggression at their clinical extremes. However, they are hypothesized to contribute to aggression through separate mechanisms. This study tested whether CU behaviors and QATs exhibited distinct profiles of heritable influences as well as independent contributions to early childhood aggression in a general population sample with enhanced sensitivity to clarify these relationships. Method: Parents of 3- to 4-year-old epidemiologically representative twins ascertained from birth records (N = 113 pairs) completed questionnaires measuring CU behaviors, QATs, and aggression. Correlation coefficients indexed overlap across behaviors. Intraclass correlations were compared between monozygotic and dizygotic twins to characterize relative genetic and environmental influences. Generalized estimating equations tested contributions of CU subdomains, verified via factor analysis, and QATs to aggression. Results: Total CU scores strongly correlated with QATs (r = 0.54) and aggression (r = 0.55), while QATs correlated moderately with aggression (r = 0.38). Among 3 identified CU factors, the uncaring factor strongly correlated with QATs (r = 0.52), while unemotional and callous factors showed small correlations (r = 0.25 and r = 0.16, respectively). QATs, aggression, and all CU factors except the callous factor showed heritable influences. Uncaring and callous factors as well as QATs demonstrated unique and shared contributions to aggression, with the callous factor being moderated by sex. Conclusion: Partially overlapping relations support distinct mechanisms whereby CU behaviors, in particular the callous factor, and QATs contribute to early aggression. In-depth social developmental assessment may enhance personalized intervention for aggression in early childhood. Plain language summary: In this cross-sectional dimensional approach, authors evaluated the extent to which callous unemotional behaviors and quantitative autistic traits showed independent contributions to aggression at age 3 to 4 years based on heritable and environmental influences that set the stage for future outcomes. In 224 preschool-aged twins, callous-unemotional behaviors and quantitative autistic traits were independently associated with reduced prosocial behavior and increased aggression, accounting for almost 30% of the variance in aggression and evidence of some shared genetic influences. Callous-unemotional behaviors accounted for a greater unique contribution to variation in aggression than autistic traits. Callous behavior is also strongly influenced by environmental factors and showed a stronger relationship with aggression in boys than in girls. These results suggest that in early childhood, quantitative autistic traits and callous-unemotional behaviors may represent distinct pathways to aggression. Diversity & Inclusion Statement: We worked to ensure sex and gender balance in the recruitment of human participants. We worked to ensure sex balance in the selection of non-human subjects. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented racial and/or ethnic groups in science.