In the largest genetic study of attention-deficit/hyperactivity disorder (ADHD) to date, an international research team has discovered the first common genetic risk factors associated with the disorder.

The findings are published in the journal Nature Genetics.

“This study marks a very important step in beginning to understand the genetic and biological underpinnings of ADHD,” said Professor Anita Thapar from Cardiff University in Wales, who leads an ADHD research group as part of the Psychiatric Genomics Consortium.

“The genetic risk variants related to this condition play a significant role in brain-related and other core biological processes. The next step is to determine the exact role of these genes in ADHD to help us inform better treatments to support those affected by the condition.”

For the study, the research team analyzed genetic data of more than 20,000 individuals with ADHD and over 35,000 non-ADHD individuals.

“We identified 12 genomic regions at which people with ADHD differed compared to unaffected individuals, and several of these regions are in or near genes with a known relationship to biological processes involved in healthy brain development,” said Dr. Joanna Martin, a research associate based at Cardiff University’s MRC Centre for Neuropsychiatric Genetics and Genomics.

Further analyses revealed that genetic risk for ADHD is shared with risk for other psychiatric and physical disorders, including depression, obesity, type 2 diabetes and lower levels of “good” HDL cholesterol.

The researchers also found that diagnosed ADHD appears to share much of the same genetic background as the traits of ADHD — such as inattention and fidgetiness — that can be measured in the general population.

Working with the Early Genetics and Lifecourse Epidemiology Consortium (EAGLE), and researchers at Queensland Institute of Medical Research (QIMR) in Australia, they compared the genetic risk for diagnosed ADHD with genetic markers associated with traits of ADHD in over 20,000 children and found a high correlation between the two, at around 97 percent.

“The correlation between these rather different definitions of ADHD suggests that clinically diagnosed ADHD may be the severe end of a continuous distribution of symptoms in the general population,” said Martin.

The collaboration consisted of European, North American and Chinese research groups that are part of the Psychiatric Genomics Consortium (PGC), as well as researchers from the Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSYCH) in Denmark.

“This is a landmark study because it involves patients from all over the world. 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,” said Thapar.

The researchers say that while the 12 genomic signals identified in this study are important, they capture only a very small amount of the risk for ADHD. Collectively, common genetic factors accounted for approximately 22 percent of the risk of ADHD.

The role of other sources of genetic risk, for example, rarer genetic changes, as well as environmental factors, will also be looked at in future studies.

Source: Cardiff University