MRI scans and DNA research revealed that children with the version of the dopamine D4 receptor gene, 7-repeat variant, with ADHD started out with the thinnest cortex areas of the brain. This area of the brain is important for controlling attention (right orbitofrontal and posterior parieto-occipital). However, 3-D MRI scans revealed that teenagers with this variant and ADHD ended up with normal thickness in the areas on the right side of the brain’s outer mantle, or cortex, resulting in clinical improvement by age 16. While 7-repeat variant was found to increase the risk for ADHD, it also indicated a higher IQ and better outcomes for teenagers and adults than those with the other two common versions of the gene.

The gene variant 7-repeat contains the same repeating sequence in its genetic code seven times. The D4 receptor gene is inherited from each parent resulting in some people inheriting two copies of the same version while others may inherit two different versions. Over 25 percent of children with ADHD have the 7-repeat gene variant while less than 20 percent of the general population have it.

In this study, researchers scanned the brains of 105 children with ADHD and 103 controls and determined their D4 gene types. Researchers continued to scan their brains through their teen years.

Participants of the study with ADHD who didn’t have at least one copy of the 7-repeat variant had significantly lower IQs than other test subjects. While only 21 percent of those with ADHD and a copy of the 7-repeat variant continued to have ADHD as adults, 50 percent of those without one 7-repeat variant continued to have pronounced ADHD symptoms into adulthood. Those with at least one copy of the 7-repeat variant also seemed to function better overall than those without that variant.

Attention deficit/hyperactivity disorder (ADHD) is a real disease associated with changes in the production of the brain chemical dopamine. Brain scans during the study revealed that people with ADHD release less dopamine into their blood than those without the disease. Drugs such as nicotine, cocaine, and methamphetamine also improve dopamine brain function. This study increases evidence that ADHD is an inherited disease with genetically determined neurobiological underpinnings.

The National Institute of Mental Health (NIMH) mission is to reduce the burden of mental and behavioral disorders through research on mind, brain, and behavior.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases.

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