From early risk via cognitive functioning to ADHD phenotype: A longitudinal study of boys at familial risk for ADHD

We examined the interplay between familial risk and the quality of the home environment and the intermediate role of cognitive functioning in the development of attention-deficit hyperactivity disorder (ADHD). Participants were 99 boys and their parents (M age = 7.34 years, SD = 0.23), who have been followed longitudinally since birth; 62 participants were followed until adolescence (M age = 13.5 years, SD = 0.95). We found that differential susceptibility to home environment in early childhood predicted the cognitive functioning (decreased executive function [EF] and increased intrasubject variability [ISV]) at elementary-school age. Specifically, in a lower quality home environment, those at high familial risk showed poor cognitive functioning (i.e., low EF and high ISV) at elementary-school age but under a supportive environment showed high cognitive functioning (i.e., high EF and low ISV), outperforming their peers at low familial risk. Moreover, child EF, but not ISV, was involved in a developmental path leading to an ADHD phenotype; it was found to mediate the relation between the early risk level (i.e., the interaction between familial risk and home environment) and child ADHD symptoms. A preliminary analysis suggests that EF may have a longitudinal effect on ADHD symptoms in adolescence; after controlling for the level of symptoms at elementary-school age, children with low levels of EF showed a significant increase in their symptoms over time. In general, our results propose a plausible mechanism that explains how the familial risk for ADHD could be translated into actual symptoms among children, at least in the case of boys.