US:Why is research on ADHD needed?

The diagnosis of ADHD is still based on clinical interviews. So far, there are no biological markers available in order to diagnose ADHD by a biological test. The pharmacological treatment of ADHD focuses on the reduction of hyperactive, impulsive and/or inattentive symptoms, but does not approach the actual cause of the disorder and can therefore not contribute to a general recovery of the patients. Additionally, we still have insufficient knowledge about the actual causes of ADHD to develop treatment possibilities that could indeed tackle the underlying causes of this disorder. Consequently, research on these causal mechanisms of the development of ADHD is necessary. With a better understanding of these processes, we hopefully can correct aberrant neuronal processes in the brain with the use of new medication or other therapy options.

ADHD has a strong genetic heritability, as approximately 70-80% of the clinical symptoms of a patient can be ascribed to heritable factors. However, the heritability of ADHD is not based on one single genetic aberration in the genetic material of a patient, but in most of the patients multiple small genetic variations play a role at the same time. Each of these variations has a small effect on the disease risk of a person. The fact that in different ADHD patients different genetic variations play a role, makes the genetic basis of ADHD even more complex. Besides, these variations also occur in healthy individuals, although ADHD patients have (a lot) more of these genetic variations. More insights into genes and genetic variants, that underlie ADHD, can improve our understanding of biological processes that differ in ADHD patients. Recently, we discovered that in ADHD the formation of connections between nerve cells during embryonic brain development progresses differently. However, the detection of genetic factors for ADHD is still a large puzzle. We think that there might be up to 1000 ADHD-related genes, and in each of these genes there are probably multiple genetic variations, which can increase the risk for ADHD. Until now, we only know very little of these genetic variants and not more than 10 different genes for ADHD have been described yet. For that reason, a lot more research is needed. Because the effects of individual genetic variants are so small, our research can only be conducted in large cohorts of ADHD patients and healthy people. Accordingly, the collaboration between several research groups, such as within the IMpACT group, is extremely important for the scientific progress. IMpACT focuses its research on ADHD in adults, i.e. persistent ADHD. This is because it is the most severe form of ADHD. There is also evidence that genetic factors of persistent ADHD play a more prominent role than in childhood ADHD. Thus, the group of adult patients seems to be very helpful for our research on discovering the genetic factors underlying the development of this disorder.