A study of 55,000 people has found the first regions of the genome linked to attention deficit hyperactivity disorder (ADHD).
Until now it has been difficult to pin down genetic variants that play a role in ADHD. It is thought to be a complex genetic condition with a large number of genes playing a cumulative role. The international study, published in Nature Genetics, identified 12 regions of the genome implicated in ADHD.
'The search for such genetic risk variants for ADHD has spanned decades but without obtaining robust results,' said Dr Ditte Demontis, an author of the paper at Aarhus University in Denmark. 'This time we really expanded the number of study subjects substantially, increasing the power to obtain conclusive results significantly.'
The team analysed genome data, comparing genetic information from 20,000 people diagnosed with ADHD with data from 35,000 people who did not have the condition. However, the regions identified in the study account for less than one percent of the genetic contribution to ADHD. In total, genetic factors are thought to account for up to 80 percent of disease risk.
The genetic variants discovered to play a role are mainly expressed in the brain, the researchers found. The variants most strongly involved tended to regulate the expression of other genes in the brain. The research supports the idea that ADHD is an 'extreme expression' of heritable traits found throughout the population, the authors conclude.
'The new findings mean that we now – after many years of research – finally have robust genetic findings that can inform about the underlying biology and what role genetics plays in the diseases and traits that are often co-occurring with ADHD,' said Professor Anders Børglum, also a study author at Aarhus University.
ADHD is thought to affect about 5 percent of children and 2.5 percent of adults. It is also thought to be widely underdiagnosed. The findings may help inform future research on the underlying biology of the condition, and the eventual goal is to develop better treatments for the condition. At present there is no cure for ADHD, but several medications are prescribed to reduce symptoms, but none without a range of common side effects.
'We have only officially diagnosed the tip of the iceberg of individuals globally with ADHD, and further gene research is highly likely to uncover more variations that may be also responsible,' Michelle Beckett, the chief executive and founder of the charity ADHD Action told The Guardian.
People with ADHD face 'incredible stigma, discrimination and denialism', Beckett said. 'This [study] almost gives us a validation, if you like, in the eyes of the people on the street and also the popular press.'