Genetic and Evolutionary Contributions to the Etiology of Attention Deficit Hyperactivity Disorder

We review progress made concerning the participation of candidate genes in the determination of attention deficit disorder with hyperactivity (ADHD) as well as recent evidence of its genetic determination based on molecular methodology. In addition to linkage analyses, we discuss recent results obtained through genome-wide association studies (GWAS). We also discuss the genetic comorbidity estimated between ADHD and major psychiatric disorders such as schizophrenia (E), major depressive disorder (MDD), bipolar disorder (BD), and autism spectrum disorders (ASD). Furthermore, we examine both the geographical distribution of DRD4 and cross-ethnic variation of ADHD risk in Chilean children. Finally, visualising ADHD from an evolutionary perspective, we suggest that behavioural traits such as hyperactivity, inattention, impulsivity, and sexual arousal, which play a role in ADHD could have had a high adaptive value during the early stages of the evolution of Homo sapiens but turned progressively less adaptive and more recently definitively disadvantageous. Attention deficit hyperactivity disorder (ADHD) is classified in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) as a neurodevelopmental disorder characterised by a persistent pattern of inattention and/or hyperactivity-impulsivity. This disorder is often associated with school learning difficulties and adjustment problems in children and adolescents and psychotropic substance consumption, alcohol abuse and risky behaviour in adults. ADHD is one of the most frequently diagnosed neuropsychiatric disorders with a prevalence between 2 and 7% worldwide [1]. As with several psychiatric disorders, there is a diversity of approaches and/or positions concerning their presumed aetiology. At one end of the spectrum are authors who still deny its existence as a disorder of biological origin and on the other, researchers who argue that it is a predominantly genetic disease with very high heritability [2].