Naturalistic Experimental Designs as Tools for Understanding the Role of Genes and the Environment in Prevention Research

Abstract

Before genetic approaches were applied in experimental studies with human populations, they were used by animal and plant breeders to observe, and experimentally manipulate, the role of genes and environment on specific phenotypic or behavioral outcomes. For obvious ethical reasons, the same level of experimental control is not possible in human populations. Nonetheless, there are natural experimental designs in human populations that can serve as logical extensions of the rigorous quantitative genetic experimental designs used by animal and plant researchers. Applying concepts such as cross-fostering and common garden rearing approaches from the life science discipline, we describe human designs that can serve as naturalistic proxies for the controlled quantitative genetic experiments facilitated in life sciences research. We present the prevention relevance of three such human designs: (1) children adopted at birth by parents to whom they are not genetically related (common garden approach); (2) sibling designs where one sibling is reared from birth with unrelated adoptive parents and the other sibling is reared from birth by the biological mother of the sibling pair (cross-fostering approach); and (3) in vitro fertilization designs, including egg donation, sperm donation, embryo donation, and surrogacy (prenatal cross-fostering approach). Each of these designs allows for differentiation of the effects of the prenatal and/or postnatal rearing environment from effects of genes shared between parent and child in naturalistic ways that can inform prevention efforts. Example findings from each design type are provided and conclusions drawn about the relevance of naturalistic genetic designs to prevention science.

Using an adoption–biological family design to examine associations between maternal trauma, maternal depressive symptoms, and child internalizing and externalizing behaviors

“…Study 2 included a linked subsample of EGDS biological mothers who were rearing a biological child (i.e., a biological sibling to an adopted child in EGDS). Children in Study 2 were assessed at around age 7 ( n = 126) as part of the ongoing Early Parenting of Children (EPoCh) study (Leve et al, 2017). Biological mother trauma was assessed over the lifetime, and her depressive symptoms were assessed from adopted child age 5 to 54 months.…”

Utilising genetically informed research designs to better understand family processes and child development: implications for adoption and foster care focused interventions

“…Research examining evocative rGE therefore allows examination of child effects on parenting, and the influence of child evoked parenting on subsequent child developmental outcomes (see Harold et al, 2013). Third, geneenvironment interaction (GxE) refers to the interaction between genes and the environment in influencing child outcomes; specifically, how environmental influences (e.g., parenting) may moderate (change the direction or magnitude of) genetic effects on child outcomes and viceversa (i.e., a child's genes may moderate the effect of the rearing environment on child outcomes; Reiss et al, 2013;Leve et al, 2017). There are two forms of gene-environment interactions that are important for intervention and prevention science.…”

“…Further, interpretation of the 'environment' relative to prevention science targets needs to be responsive to the complexities of family, community and wider environmental impacts on outcomes. (2) ensure that the intervention targets the specified environmental mechanism, and that there is overlap with quantitative genetic studies regarding the measurement of this mechanism; (3) employ designs and samples that identify individuals and conditions under which the intervention is most effective (Leve et al, 2017). These steps will allow quantitative genetics studies to map onto an intervention mechanism of change, thus intervention can be appropriately modified, taking into account inherited characteristics to provide more precise mechanisms of change.…”

The Implications of Genetics for Prevention and Intervention Programming

“…Another avenue for the inclusion of genetics in prevention work may lie in the natural experimental designs available within the human population (Leve et al, 2017). Leve and colleagues (2017) explore these possibilities, with special focus on three design types:children…”