A new study by the National Institute of Mental Health (NIMH) has found that a gene can predict if someone is at risk for Attention Deficit Hyperactivity Disorder (ADHD). The NIMH study found that the gene, a 7-repeat variant of the dopamine D4 receptor, also indicates better outcomes and higher IQs than two other genes sometimes found in children with ADHD. The gene is linked to the brain’s production of dopamine.
More research into this variant could lead to treatments that will help children recover more quickly from ADHD. Currently, the disorder is treated with a combination of drugs and behavioral therapy. But some of the drugs have serious side effects. Last month, a University of California study found that the common ADHD drug Ritalin could stunt the growth of children taking it. And additional studies have hinted that the drug could increase a child’s risk for developing cancer.
The NIMH study involved 105 children with ADHD, and 103 healthy control subjects. All of the subjects were followed through their teen years. The 7-repeat variant, so named because it contains the same sequence in its genetic code seven times, was found in nearly one fourth of the children with ADHD. These children all had at least one copy of the 7-repeat version.
The NIMH study found that brain areas that control attention were the thinnest in children with ADHD who carried the 7-repeat variant. But in these children, those areas normalized in thickness during their teen years. This coincided with improvement of ADHD symptoms. Researchers did not see similar improvement in ADHD patients with other gene variants linked to the disorder.
The ADHD children who had the 7-repeat variant also had better outcomes than the children with other gene variants. ADHD participants in the study who lacked at least one copy of the 7-repeat variant had lower IQs. Of those who had follow-up evaluations six years after the study started, 50-percent without the variant still had pronounced ADHD symptoms. In the group with at least one copy of the 7-repeat variant, only 21-percent still had pronounced symptoms.
However, some of the healthy subjects in the study also had at least one copy of the 7-repeat variant. So while the gene is a factor for ADHD risk, it is not a determining one. Rather, NIMH researchers believe that genes, coupled with other non-genetic factors, play a part in the disorder.
Another study published this month in the Archives of General Psychiatry found that the brains of children with ADHD produce less dopamine, not more as was previously thought. Individuals with ADHD are known to have a higher risk of developing substance abuse problems than the general population. Low dopamine production may explain that. Drugs like nicotine, cocaine and methamphetamine increase dopamine production, something that could cause a person with ADHD to crave such substances.