probands to help them overcome some of their early difficulties with inattention, hyperactivity and impulsivity. Alternatively, our results could be reflecting the impact of DRD1 on changes in attentional control on working memory performance rather than vice versa. However, we have approached this study from the classic endophenotype model in which an intermediate cognitive phenotype (i.e. working memory) is hypothesized to contribute to the development of and recovery from a more complex psychiatric phenotype (i.e. ADHD). As such, we sequentially structured our analyses in the way laid out in the methods section and at no point made Digit Span the dependent variable and CBCL-AP a predictor variable. Therefore, we have no empirical data to support the inverse association (i.e. DRD1 facilitates improvement in attentional control to enhance working memory performance), though acknowledge that this association possibly exists to at least some degree.
