There is a large genetic component to attention deficit/hyperactivity disorder (ADHD), a study published recently in Nature Genetics has confirmed. The study assessed 20,183 individuals diagnosed with ADHD and 35,191 controls, finding variants in 12 independent loci which all contribute to ADHD.

The study was a global one, with collaboration between groups in Europe, North America and China. This was an important component of the study, with Dr Anita Thapar of Cardiff University School of Medicine noting that: “This large number of patient samples has been lacking for ADHD, meaning our understanding of ADHD genetics has lagged behind physical disorders and other psychiatric disorders like schizophrenia and depression.”

Dr Anders Børglum, professor at Aarhus University, said the findings could give a better understanding of the development of ADHD: “For example, some of the implicated genes influence how brain cells communicate with each other, while others are important for cognitive functions such as language and learning.

“The risk variants typically regulate how much a gene is expressed, and our results show that the genes affected are primarily expressed in the brain.”

In addition to the specified loci, the scientists identified more than 40 diseases or traits which have genetic signals considerably overlapping with ADHD, with positive correlations to major depression, obesity, type 2 diabetes and insomnia.

They also found that diagnosed ADHD has a great deal genetically in common with traits of ADHD found in the general population, such as inattention and restlessness. The genetic risk for diagnosed ADHD was measured against genetic markers associated with ADHD traits in more than 20,000 children, and found there was a high correlation between the two, at around 97%. This suggests that the more genetic risk variants in an individual, the greater their risk of developing ADHD.

The researchers said the next step is to conduct an even larger study of around 100,000 individuals, with the aim of finding other genes involved in ADHD. Scientists must also determine the specific role genes have in ADHD, to inform treatment of the condition.