The effect of smoking during pregnancy on severity and directionality of externalizing and internalizing symptoms: A genetically informed approach

The objective was to examine the association between maternal smoking during pregnancy (SDP) and (I) severity and (II) directionality of externalizing and internalizing symptoms in a sample of sibling pairs while rigorously controlling for familial confounds. The Missouri Mothers and Their Children Study is a family study (N = 173 families) with sibling pairs (aged 7 to 16 years) who are discordant for exposure to SDP. This sibling comparison study is designed to disentangle the effects of SDP from familial confounds. An SDP severity score was created for each child using a combination of SDP indicators (timing, duration, and amount). Principal component analysis of externalizing and internalizing behavior, assessed with the Child Behavior Checklist and Teacher Report Form, was used to create symptom severity and directionality scores. The variance in severity and directionality scores was primarily a function of differences between siblings (71% and 85%, respectively) rather than differences across families (29% and 15%, respectively). The severity score that combines externalizing and internalizing symptom severity was not associated with SDP. However, a significant within-family effect of SDP on symptom directionality (b = 0.07, p = 0.04) was observed in the sibling comparison model. The positive directionality score indicates that SDP is associated with differentiation of symptoms towards externalizing rather than internalizing symptoms after controlling for familial confounds with a sibling comparison model. This supports a potentially causal relationship between SDP and externalizing behavior.</p

The Importance of the Prenatal Environment in Behavioral Genetics: Introduction to Special Issue

We introduce and discuss a special issue on prenatal factors in genetics research, that includes 14 papers ranging from studies on chorionicity, smoking during pregnancy, and more general prenatal risks to papers about theory, methods and measurement. There are two review papers, one focused on chorioncity and the second on pre- and perinatal ischemia-hypoxia, that help to frame the state of research in these areas with a focus on the relevance across multiple fields of study. Taken together, these papers clearly demonstrate the importance of considering prenatal environment influences on functioning in offspring across the lifespan while also underscoring the importance of using genetically informed designs as a means to clarify causality