Featured Published Manuscript of the Month:   January, 2019

Chosen and summarized by:                                       Ashlee A. Moore

Waller, R., Hyde, L.W., Klump, K.L., & Burt, S.A. (2018). Parenting is an environmental predictor of callous-unemotional traits and aggression: A monozygotic twin differences study. Journal of the American Academy of Child and Adolescent Psychiatry, 57(12), 955-963.

Corresponding Author:  S. Alexandra Burt ([email protected]), Michigan State University

   This featured study investigated the direct environmental impact of parental harshness and parental warmth on callous-unemotional (CU) traits and aggression in a sample of 454 monozygotic (MZ) twins (227 twin pairs). The MZ differences study design allows for the direct examination of parenting effects without the confounding effects of genetics, passive gene-environment correlation, and evocative gene-environment correlation. This MZ differences study was comprised of twins aged 6-11 years, recruited from south-central Michigan, and oversampled for families living in poverty. The sample was 49% female with ethnic group membership comparable to that of the state of Michigan (81% non-Latino white, 6% African-American, 3% Latinx, 1% Asian, 1% Pacific Islander, & 6% not specified). Parental harshness, parental warmth, aggression, and CU traits were assessed via parent report measures.

Key findings:

·             Co-twin differences in parental harshness predicted co-twin differences in CU traits and aggression, such that the twin receiving more parental harshness displayed higher levels of CU traits and aggression.

·            Co-twin differences in parental warmth predicted co-twin differences in CU traits, such that the twin receiving more parental warmth displayed lower levels of CU traits.

·         The relationship between parental harshness and aggression was moderated by family income, with a greater magnitude of effect in twins from lower-income families. No additional associations were moderated by twin sex, twin age, or family income.

Key implications:

·            Most studies of CU traits have not attempted to disentangle genetic effects from unmeasured gene-environment correlation (such as the case when a parent’s genes predispose their child to have a biological risk for CU and also predispose the parent to provide an inadequate caregiving environment). Such methodological limitations may increase the reported heritability of CU traits, and allow researchers to conclude that parenting does not have a significant influence on CU.

·           The unique design of the current study allowed researchers to directly estimate the effects of the parenting environment, and they conclude that there is strong evidence for the effects of parenting on CU traits over and above the known genetic effects. That is, parental harshness increases aggression and CU traits, and parental warmth decreases CU traits.

·           The authors propose the following developmental pathway: “… parental warmth is thought to increase the quality of the parent child relationship and scaffold emotional sensitivity, which enhances children’s ability to develop empathy, thereby lowering risk for CU traits.” (pp. 962)