Some say the condition is being over-diagnosed in the United States, exposing children unnecessarily to medication. Others argue it is not treated often enough. Earlier studies have shown that scans can detect structural differences in ADHD sufferers' brains as well as abnormalities in brain activity, and scientists suspect that defects in genes relating to the brain chemical dopamine probably are involved. The latest study, conducted at Massachusetts General Hospital in Boston and published in this week's issue of The Lancet medical journal, is the first to show a measurable biochemical abnormality in people with the disorder. The Boston scientists have come up with the most direct indicator to date, measuring the biochemical balance in the brain by counting the number of dopamine transporters.
Dopamine is associated with movement, thought, motivation, and pleasure.
One brain cell signals another by squirting dopamine. Then the first cell mops up the released chemical with a structure called a dopamine transporter. The researchers scanned the brains of six adults diagnosed with ADHD and 30 healthy people of the same age after injecting both groups with a chemical agent that attaches to the dopamine transporter. The ADHD sufferers had 70 percent more dopamine transporters than their healthy counterparts. The scientists could not tell, however, whether that was a cause or an effect of the disorder.