Shared genetic influences do not explain the association between parent-offspring relationship quality and offspring internalizing problems: results from a Children-of-Twins study

Background. Associations between parenting and child outcomes are often interpreted as reflecting causal, social influences. However, such associationsmay be confounded by genes common to children and their biological parents. To the extent that these shared genes influence behaviours in both generations, a passive genetic mechanismmay explain links between them. Here we aim to quantify the relative importance of passive genetic v. social mechanisms in the intergenerational association between parent-offspring relationship quality and offspring internalizing problems in adolescence. Methods. We used a Children-of-Twins (CoT) designwith data fromthe parent-based Twin andOffspring Study of Sweden (TOSS) sample [ 909 adult twin pairs and their offspring; offspringmean age 15.75 (2.42) years], and the child-based Swedish Twin Study of CHild and Adolescent Development (TCHAD) sample [ 1120 adolescent twin pairs; mean age 13.67 (0.47) years]. A composite of parent-report measures (closeness, conflict, disagreements, expressions of affection) indexed parent- offspring relationship quality in TOSS, and offspring self-reported internalizing symptoms were assessed using the Child Behavior Checklist (CBCL) in both samples. Results. A social transmissionmechanism explained the intergenerational association [ r = 0.21 (0.16-0.25)] in our best-fitting model. Apassive genetic transmission pathwaywas not found to be significant, indicating that parental genetic influences on parent-offspring relationship quality and offspring genetic influences on their internalizing problemswere non-overlapping. Conclusion. These results indicate that this intergenerational association is a product of social interactions between children and parents, withinwhich bidirectional effects are highly plausible. Results fromgenetically informative studies of parentingrelated effects should be used to help refine early parenting interventions aimed at reducing risk for psychopathology.