ADHD a risk factor for other mental illnesses
New study provides insights and recommendations for clinical practice.
Attention deficit hyperactivity disorder (ADHD) is a neural developmental disorder that occurs among children and young people, which in two thirds of cases carries over into adulthood. It is estimated to affect around 5 percent of children and young people and about 2.5 percent of adults worldwide. A recently published study by the Chair of Epidemiology at the University of Augsburg in the renowned journal BMJ Mental Health shows that ADHD often occurs in association with severe depression, post-traumatic stress disorder, the eating disorder Anorexia nervosa, as well as attempted suicide. “In observational studies, ADHD has been associated with mood and anxiety disorders, but up until now it was unknown whether it is causally related to other mental illnesses,” explains Professor Christine Meisinger, researcher at the Chair of Epidemiology and first author of the study. In order to find this out, the researchers used Mendelian randomisation, a technique in which genetic variants are used as proxies for a particular risk factor (in this case ADHD) to obtain genetic evidence for a particular outcome, in this study for seven common mental illnesses: severe clinical depression, bipolar disorder, anxiety disorder, schizophrenia, post-traumatic stress disorder (PTSD), Anorexia nervosa, and attempted suicide. “Understanding the causal relationships of attention deficit/hyperactivity disorder with mental disorders and suicide attempt: a network Mendelian randomisation study,” BMJ Mental Health (2023). DOI: 10.1136/bmjment-2022-300642 
“Our study delivers new insights into the complex network of relationships between mental disorders and their connection to ADHD. There is indication of a causal relationship between ADHD and severe clinical depression. Both mental disorders, either alone or together, increase the risk for post-traumatic stress disorder and attempted suicide. However, an increased risk for Anorexia nervosa can be exclusively traced back to ADHD. On the other hand, there is no indication of a causal relationship between ADHD and bipolar disorder, anxiety disorder, and schizophrenia,” explains Dr Dennis Freuer, who is responsible for statistical analysis and co-author of the study.
Although Mendelian randomisation has methodological limitations, the findings of the current study are so significant they should encourage clinicians to be more proactive in treating people with ADHD, say Meisinger and Freuer. “This study provides new insights into the pathways between mental disorders. Patients with ADHD should therefore be monitored in clinical practice for the mental disorders investigated in this study and preventive measures initiated where appropriate,” the two authors explain.
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