ADHD is one of the most common mental health conditions, and it is estimated to impact 5 - 8 percent of boys, according to the World Health Organization. Symptoms include impulsivity, an inability to stay focused, and excessive talking, fidgeting or movements that are not appropriate for the setting. Now scientists have revealed differences in gene expression in the brains of people with ADHD compared to unaffected individuals. ADHD patients had changes in genes encoding for neurotransmitters, which carry crucial signals among neurons. The findings have been reported in Molecular Psychiatry.
This work, which assessed post-mortem brain tissue from affected individuals, is the first ADHD study of its kind. While other research has examined brain structure using tools like MRIs, this research shows which genes might be involved in ADHD and how they may be influencing the disease. RNA from two parts of the brain that have previously been associated with ADHD, the caudate nucleus and the frontal cortex, was analyzed. Since active genes are transcribed from DNA to RNA, this reveals which genes were being expressed in those regions.
The scientists found expression differences in neurotransmitter genes, with glutamate neurotransmitters being particularly affected. Glutamate is thought to play a role in attention and learning. Changes occurred in both regions that were analyzed, although there were more differences in the anterior cingulate cortex of ADHD brains compared to controls; there were still differences in the caudate nucleus, but there weren't as many.
"Multiple types of genomic studies are pointing towards the expression of the same genes," said study leader Gustavo Sudre, Ph.D., an associate investigator in the NHGRI's Intramural Research Program. "Interestingly, these gene-expression differences were similar to those seen in other conditions, which may reflect differences in how the brain functions, such as in autism."
"The study advances our understanding of ADHD by showing how the condition is tied to changes in how certain genes are expressed in the brain. This allows us to inch closer to understanding how genomic differences alter gene expression in the brain and contribute to ADHD symptoms," said study supervisor Philip Shaw, M.D., Ph.D., a senior investigator at the NHGRI.
Researchers often have to model human disease in animals, so this study carries particular significance because it used human tissue to look at the genes that were affected in ADHD.
Sources: National Institutes of Health, Molecular Psychiatry