Discoveries on the genetics of ADHD in the 21st century: new findings and their implications

Attention Deficit/Hyperactivity Disorder (ADHD) like all common medical conditions is explained by the contribution of multiple genes and environmental risk factors. Family and twin studies consistently have observed a prominent genetic contribution but it is only recently that technological advances now have enabled direct genetic investigations. In this article I selectively review genetic findings on ADHD over the last five years and focus on their implications for the conceptualization of ADHD and future clinical practice. Recent, large-scale family studies and gene discoveries reveal the strong genetic overlaps between ADHD and Autism Spectrum Disorder, as well as Intellectual Disability. These findings highlight its neurodevelopmental nature. ADHD however shows substantial genetic correlations with a much broader group of neuropsychiatric disorders, especially major depressive disorder as well as with non-psychiatric characteristics. I discuss a few different explanations that might underlie these links. ADHD while usefully conceptualized as a disorder in clinical practice, is commonly viewed as a continuously distributed trait in the fields of developmental psychopathology and epidemiology. Recent genome-wide association study findings consistent with previous twin studies, highlight that ADHD appears to lie at the extreme of a continuously distributed dimension akin to hypertension and blood pressure. New genetic findings on developmental continuity and change are discussed and I emphasize the need for a developmental perspective to genetic studies. Finally, I consider potential future directions for scientists and the implications of new genetic findings for clinicians