Sibling differences in low birth weight, dopaminergic polymorphisms, and ADHD symptomatology: evidence of GxE.

Low birth weight has been found to increase the risk of attention-deficit hyperactivity disorder (ADHD) in children. However, few studies adequately control for shared environmental influences (e.g., concentrated disadvantage, family structure) or examine whether interactions between birth weight and genetic factors predict ADHD. The present study addresses these limitations in prior research by examining a) whether sibling differences in low birth weight status are significantly predictive of sibling differences in behaviors symptomatic of ADHD and b) whether sibling differences in dopaminergic genes interact with sibling differences in low birth weight status to predict sibling differences in ADHD symptomatology. The results suggest that low birth weight siblings are at significantly greater risk of exhibiting symptoms of ADHD during childhood relative to their normal birth weight siblings. Moreover, possessing greater genetic risk on three dopaminergic genes (DAT1, DRD2, and DRD4) relative to a sibling appears to exacerbate the link between sibling differences in birth weight and sibling differences in ADHD symptomatology. Limitations and directions for future research are discussed.