ebook_ADHD2019

116 Rohde, Buitelaar, Gerlach & Faraone Thus, the evidence of a genetic based disorder is against the idea of a disorder caused by modern society demands. Moreover, there is substantial medical lite- rature describing what is now called ADHD since the beginning of the previous century. Reports of clinical presentations like ADHD can be traced to writings in ancient Greece. 11 Additionally, one of the most cited studies in the entire literature on ADHD assessed more than 100 papers addressing the frequency of the disorder in coun- tries from all continents. The main findings showed that both the frequency of the disorder is similar in culturally very different countries and the prevalence is not different between North-America and Europe, reinforcing that culture does not cause the disorder. 12 A variant of this myth is the one that the frequency of the disorder is increasing in the population in the last decades due to modifications in our society that is only focused on performance. Our group conducted a large review of the litera- ture (more than 130 studies) across the last three decades on the frequency of the disorder and clearly documented that there is no increase worldwide in the rates of the disorder during this time period in population samples (see Figure 6.2). 13 Re- cently, authors from Sweden replicated the same finding in a population sample of more than 19200 twins assessed at 9-years of age from 2004 and 2014. 14 However, it is important to note that the modern understanding of mental di- sorders suggests that they are determined by the interaction between genes and environment. 15 Therefore, the environment plays a role in the manifestation of ADHD symptoms. In this way, an individual with a strong genetic predisposition for ADHD might present symptoms independently of the environment while pe- ople with low genetic predisposition for the disorder might never manifest symp- toms even in a very demanding environment. The demands of the environment might be more relevant for those halfway between these two extremes. Thus, the modern western demand of higher inhibitory control, planning and focus to be successful is not the cause of the disorder, but can trigger ADHD symptoms in those with the genetic vulnerability while a supportive environment can buffer genetic predisposition. HOW CAN MY CHILD HAVE ADHD IF HE/SHE IS NOT HYPERACTIVE? People tend to associate ADHD with a stereotype of a young boy who never stops! However, as discussed in the first chapter, ADHD is composed of symptoms in one of the two dimensions: inattention and/or hyperactivity/impulsivity. Thus, whi- le some individuals might have predominantly hyperactive symptoms, others have predominantly inattentive symptoms and there are people with symptoms in both dimensions.