Intergenerational transmission of ADHD behaviors: genetic and environmental pathways

Background: We investigate if covariation between parental and child ADHD behaviors can be explained by environmental and/or genetic transmission. Methods: We employed a large children-of-twins-and-siblings sample (N=22,350 parents & 11,566 8-year-old children) of the Norwegian Mother, Father and Child Cohort Study (MoBa). This enabled us to disentangle intergenerational influences via parental genes and parental behaviors (i.e., genetic and environmental transmission, respectively). Fathers reported on their own symptoms and mothers on their own and their child’s symptoms. Results: Child ADHD behaviors correlated with their mother’s (0.24) and father’s (0.10) ADHD behaviors. These correlations were largely due to additive genetic transmission. Variation in children’s ADHD behaviors was explained by genetic factors active in both generations (11%) and genetic factors specific to the children (46%), giving a total heritability of 57%. There were small effects of parental ADHD behaviors (2% environmental transmission) and gene-environment correlation (3%). The remaining variability in ADHD behaviors was due to individual-specific environmental factors. Conclusions: The intergenerational resemblance of ADHD behaviors is primarily due to genetic transmission, with little evidence for parental ADHD behaviors causing children’s ADHD behaviors. This contradicts theories proposing environmental explanations of intergenerational transmission of ADHD, such as parenting theories or psychological life history theory.