Background From a functionalist perspective, parenting behaviors have adaptive functions and are partly expressions of genetic variation. Maternal genes that have effects on children are often referred to as indirect maternal genetic effects. Indirect genetic effects provide a means for measuring the role of parenting without the need for specifying the relevant parental behaviors. We studied indirect maternal genetic effects to address both the importance and commonality of parenting across the internalizing–externalizing spectrum of behavior problems in childhood. We further addressed how indirect genetic effects impact our understanding of direct genetic effects if not accounted for. Methods Utilizing data from the Norwegian Mother, Father, and Child Cohort Study (MoBa), our analyses involved 42,423 children and their mothers. Both pedigree and genotype data were used to infer genetic relationships. We applied multivariate latent variable models to distinguish indirect maternal genetic effects and direct offspring genetic effects on seven measures of internalizing–externalizing behaviors. Results Our findings indicate significant maternal genetic influences, explaining 7%–18% of the variance across internalizing–externalizing behaviors. A general maternal effect common across behaviors could adequately account for most of the variability. The analyses further indicate that direct child genetic effects appear smaller and more complex when indirect maternal genetic effects are modeled simultaneously. Conclusions By summarizing the effects of parenting with indirect maternal genetic effects, we show a substantial contribution of parents with respect to internalizing–externalizing behaviors in childhood. Although parenting is multifaceted, the effects of parenting are general and can succinctly be described as a single common dimension. Further, our study demonstrates that direct genetic effects appear smaller and more complex when maternal genetic effects are accounted for, highlighting the confounding potential of parental effects in understanding the role of genetic differences in child psychopathology.
Eilertsen et al. (Tue,) studied this question.