In child development studies, the factors influencing a particular variable will usually have a genetic or an environmental source. Research frequently suggests that some combination of the two is at work. Indeed, that there is almost always interplay between genetic and environmental influences is becoming the generally accepted wisdom.

But how useful can it be to leave research findings in this betwixt and between condition, unless there is some attempt to decide how genetic and environmental factors combine?

Taking the extra step is especially important in investigations of parental influences on children, because they will have roots in both domains. But, in the absence of any twin study, it can be difficult to determine which influences are which.

A team of researchers from the University of North Carolina at Chapel Hill and Pennsylvania State University is behind one of a few studies that have tried to understand this interactive process in the context of mothers’ influences on their children’s behavior.

W. Roger Mills-Koonce and his colleagues investigated the relationship between the presence of dopamine receptor gene DRD2 A1+ in mothers and children, and maternal sensitivity. They considered how the characteristics of mother and child mediate this relationship and how maternal sensitivity might moderate the association between the gene and child affective problems at age three.

The team studied 172 parent-child relationships from birth to 36 months (at six, 12 and 36 months) using standardized interviews, free-play interactions and DNA samples taken from inside the cheek of the mother and child.

Their main findings indicate that children who carry the DRD2 A1+ gene receive less sensitive care and show more "negative mood" towards parents than children who do not (the reasons are as yet unclear). No mediating factors were found to alter this relationship.

The results also suggest that early maternal sensitivity has a significant effect on later child affective problems, so that children with the DRD2 A1+ gene and a more sensitive mother have lower levels of affective problems than those with the gene and a less sensitive mother.

The authors conclude that their results highlight the complexity and importance of understanding the interplay between gene and environment (G x E) in any context, but especially in relation to understanding family systems.

“These analyses,” they write, “begin to address many long-standing questions regarding the role of genetics in family functioning, the role of the child as an organizer of parenting behavior, and the role of family experience in genetic expression. Unfortunately, a critical piece of the puzzle in these analyses remains missing. Despite examination of mother-reported temperament and observed child behavior, we were unable to identify a behavioral process by which children with DRD2 A1+ differentially evoke less sensitive care giving.”

The edition of Development and Psychopathology that includes the Mills-Koonce investigation is entirely devoted to studies that are trying to improve understanding of G x E interactions – work which in time,should allow more informed decisions about what interventions will work under given family circumstances – and why.

• Summary of Mills-Koonce R, Propper C, Gariepy J, Blair C, Garrett-Peters,P and Cox M (2007) “Bidirectional genetic and environmental influences on mother and child behaviour: the family system as the unit of analyses”, Development and Psychopathology, 19, pp1073-1087

• This story was first published in Prevention Action on January 9th 2008.