The Aetiology of Attention-Deficit/Hyperactivity Disorder: Key Insights from Our Systematic Review

In this overview, we summarise key findings from our systematic review on the aetiology of ADHD. The efforts to identify the causes of ADHD have been extensive and the findings may be useful for developing treatments and reducing its incidence. Over the past few decades, modern statistics have been applied to data sets of twin and family studies that can discern the extent to which variation in symptoms is attributable to the social, rearing or familial environment, to unique events that befall only one family member, or to genetics. These studies consistently support the strong level of genetics contributing to this disorder (70-80%) with the residual variation accounted for by unique, non-shared events. Advances in molecular genetics have established the disorder as polygenic and thus dimensional in nature. Additionally, epidemiological and naturalistic research designs have identified two independent, environmental causes of ADHD; occurring rarely. We discuss the numerous implications of these results for the categorisation of ADHD, clinical practice, theoretical conceptualisations of executive functioning, and usefulness in rebutting misinformation propagated by the trade media.