All large population-based administrative studies currently indicate a significant comorbidity of adult attention deficit hyperactivity disorder (ADHD) with addictive, anxiety and in particular affective disorders. In these investigations the risk for one of these comorbid disorders increased with increasing age of the ADHD patients. The most recent genome-wide association and correlation studies also revealed indications for joint genetic risk factors of ADHD with, in particular unipolar depression, bipolar disorder, autism spectrum disorders, Tourette's syndrome and to a lesser extent schizophrenia. The only psychiatric disorder that was negatively correlated with ADHD was anorexia nervosa. Additionally, cannabis and cocaine use were significantly positively genetically correlated with ADHD. Furthermore, an increased occurrence of some specific somatic diseases could be found in patients with adult ADHD. In particular, obesity, migraine, sleep disorders, asthma and celiac disease showed a significantly positive association with ADHD in several studies. No association was found between ADHD and cardiovascular disease. Here as well there are initial indications of joint genetic risk variants; however, data are still sparse and additional studies are needed before valid conclusions can be drawn. To some extent these associated somatic diseases might be differential diagnoses rather than true comorbidities, for example, obstructive sleep apnea syndrome (OSAS) can lead to ADHD-like symptoms that disappear when the OSAS is sufficiently treated. Therefore, it is important to keep the co-occurrence of psychiatric and somatic disorders in mind during the diagnostics and treatment of adult ADHD patients to improve their general health and quality of life.
Keywords: Addiction; Epidemiology; Genetics; Psychiatric disorders; Somatic diseases.