ADHD is a heritable disorder, which means that genes contribute to the risk for getting the disorder. There are hundreds or even thousands of genes that contribute to ADHD, and while each single gene itself will not cause ADHD, together they contribute to the risk. But it is important to note that genes are not everything – environmental influences, such as preterm birth or exposures during pregnancy, may also contribute to the risk for ADHD.
Individuals with ADHD sometimes have other co-occurring conditions, such as mood disorders, obesity and substance abuse. This has led to the important research question of why do these conditions often co-occur with ADHD. Are there shared risk factors?
We know that people with ADHD not only tend to have a family history of ADHD, but they also are more likely to have siblings or parents with certain other co-occurring traits and disorders. This suggests that there are overlapping familial risk factors – which could be genes – between ADHD and other conditions.
A very large and recent genetic study that examined thousands of common genetic markers across our DNA, identified for the first time several genes that underlie risk for ADHD2. This information allowed us to investigate the genetic overlap between ADHD and other disorders using actual genetic data. In our new paper published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging3, we selected a bunch of genetic markers that most strongly underlie risk for ADHD, identified in the previous genetic study, and tested if they showed an overlap with other traits and disorders that often co-occur with ADHD. We tested this on a very large sample of 135,000 people in the UK. We found that some of the genetic risk factors were shared between ADHD and co-occurring conditions in the general population, specifically – atypical cognitive functioning, higher body mass index, neurotic behaviour, anxiety, depression, risk-taking behaviour, smoking and alcohol use.
Our study findings suggest that genes do, at least to some extent, explain the overlap between ADHD and co-occurring conditions. These genetic factors contribute to cognitive functioning, body mass index, mood symptoms and substance use in the general population.
The aim of this research is to further our understanding of ADHD and co-occurring traits and disorders. A better understanding of why ADHD often co-occurs with other conditions may help in the development of new treatments. Also, if we know how to predict which individuals with ADHD are at risk for other co-occurring disorders, we will be in a better position to offer early interventions that could prevent such further problems from developing.
Ebba Du Rietz and Jonna Kuntsi
- Faraone SV, Perlis RH, Doyle AE, Smoller JW, Goralnick JJ, Holmgren MA, Sklar P. Molecular genetics of attention-deficit/hyperactivity disorder. Biol Psychiatry. 2005; 57:1313–1323. doi: 10.1016/j.biopsych.2004.11.024.
- Demontis D, Walters RK, Martin J, et al. Discovery of the first genome-wide significant risk loci for ADHD. bioRxiv 145581. 2017. doi: https://doi.org/10.1101/145581.
- Du Rietz E, Coleman J, Glanville K, Wan Choi S, O’Reilly PF, Kuntsi J. Association of polygenic risk for attention-deficit/hyperactivity disorder with co-occurring traits and disorders. Biol Psychiatry: CNNI. In press. doi: https://doi.org/10.1016/j.bpsc.2017.11.013