The role of genetic factors in adult ADHD
Attention deficit/hyperactivity disorder, ADHD, is one of the most common neuropsychiatric disorders of childhood. Worldwide, 3% of children are affected with the disorder. Key symptoms of ADHD include age-inappropriate hyperactive and impulsive behaviour and/or a reduced ability to focus attention. Clinically, three different ADHD subtypes are classified, a primarily inattentive subtype, a primarily hyperactive/impulsive subtype, and a combined subtype in which patients show deficits in both domains. At the level of the brain, small aberrations in both structure and activity of specific brain regions, as well as the connectivity between brain regions have been observed in children and adults with ADHD (Valera et al., 2007; Schneider et al., 2006; Makris et al., 2008; Pavuluri et al., 2009; Broyd et al., 2009).
Although ADHD has classically been viewed as a disorder of children, more than half of the patients carry symptoms, or even the full ADHD-diagnosis, into adulthood (Faraone et al., 2006). The prevalence of ADHD in adults lies between 1% and 4% (Kessler et al., 2006; Polanczyk et al., 2007; Kooij et al., 2005). Adult patients have difficulties in the social, educational and professional fields, such as developing or maintaining stable social relationships, completing educational programmes and holding down jobs. Untreated adults with ADHD often have chaotic life-styles: They may feel that it is impossible to get organised, or remember and keep appointments. Unfortunately, many adults who have the disorder are not aware of this. As symptoms in adults tend to be more varied than symptoms seen in children, health care professionals need to consider a wider range of symptoms when assessing adults for ADHD.
An expert calls "ADHD […] one of the costliest medical conditions in the US", the average loss of income for ADHD adults being $10,000 to $40,000 a year (see also Kessler et al., 2005; Kessler et al., 2006). In addition, patients are at increased risk of comorbidity, including aggression-related disorders and addiction. More than 60% of the adult patients have at least one additional psychiatric diagnosis. Substance abuse disorders are seen in 10% of the patients.