Parenting Is an Environmental Predictor of Callous-Unemotional Traits and Aggression: A Monozygotic Twin Differences Study.

OBJECTIVE: Callous-unemotional (CU) traits increase risk for children to develop severe childhood aggression and conduct disorder. CU traits are typically described as highly heritable, and debate continues about whether the parenting environment matters in their etiology. Strong genetically informed designs are needed to test for the presence of environmental links between parenting practices and CU traits. Our objective was to determine whether parental harshness and parental warmth were related to children's aggression or CU traits when accounting for genetically mediated effects.
METHOD: We examined 227 monozygotic twin pairs (454 children) drawn from population-based and at-risk samples of twin families, leading to oversampling of twins living in poverty. We computed multi-informant difference scores combining mother and father reports of their harshness and warmth toward each twin, and differences in mother reports of each twin's aggression and CU traits.
RESULTS: Twin differences in parental harshness were related to differences in both aggression and CU traits, such that the twin who received harsher parenting had higher aggression and more CU traits. Differences in parental warmth were uniquely related to differences in CU traits, such that the twin receiving warmer parenting evidenced lower CU traits. These effects were not moderated by child sex, age, or family income, with the exception that the relationship between differential parental harshness and differential child aggression was stronger among low-income families.
CONCLUSION: Parenting is related to child CU traits and aggression, over and above genetically mediated effects, with low parental warmth being a unique environmental correlate of CU traits.