A genome-wide association study (GWAS) has uncovered the first genetic risk loci for attention deficit hyperactivity disorder (ADHD). The findings shed light on the biological pathways underlying the disorder and might pave the way to new treatments.

ADHD is a neurodevelopmental behavioural disorder characterized by severe impulsivity and inattention. The condition affects ~5% of children and ~2.5% of adults globally. Previous studies of ADHD have indicated a substantial heritable component of the disorder, but researchers have been unable to identify individual risk loci until now. “It is important to understand the causes and disease mechanisms of ADHD in order to lay the foundation for better treatment of the condition, which is impairing the lives of many millions of people around the world,” remarks study author Anders Børglum.

“I realized that solving this problem required many DNA samples from people with and without ADHD,” explains study author Stephen Faraone. “So, I created the ADHD Molecular Genetics Network, funded by the US National Institute of Mental Health.”

The researchers performed a GWAS in 20,183 individuals diagnosed with ADHD and 35,191 healthy individuals without ADHD. The results revealed 12 risk loci, most of which were associated with genes expressed in the brain, including FOXP2, DUSP6 and SORCS3. Many of the identified variants were in genes involved in brain circuit development and cognitive functions such as learning and language.

Interestingly, the team found that the ADHD-associated variants were linked to traits of impulsivity and inattention in people without ADHD in the general population. ADHD risk alleles were also associated with an increased risk of other traits and disorders, such as depression, type 2 diabetes mellitus, obesity and insomnia.

The loci that the researchers identified only account for a small fraction of the total genetic risk of ADHD. “The vast majority of ADHD genetics is still undiscovered and will require even larger studies,” remarks Børglum.

Many of the identified variants were in genes involved in brain circuit development and cognitive functions such as learning and language

The investigators also note that more work is required to understand the role of the identified genetic loci in ADHD pathogenesis. “Future work will need to map out the biological pathways implicated by our data with the hope that, someday, we will be able to develop treatments to cure or prevent the disorder,” concludes Faraone.