For the current study, the researchers scanned and determined the D4 gene types of 105 children with ADHD and 103 healthy controls and re-scanned them through their teen years.
They found that nearly one-fourth of youth with ADHD and in about one-sixth of the healthy controls had at least one copy of the 7-repeat version. Nearly two thirds of the ADHD youth and three-fourths of the healthy controls had the most common 4-repeat version; fewer than one-tenth in each group had a 2-repeat version.
While the 7-repeat version was linked to thinner attention-controlling cortex in both ADHD and healthy subjects, it appeared to confer advantage only among youth with ADHD. For example, participants with ADHD who lacked at least one copy of this 7-repeat variant had significantly lower IQs, and more than half of them still had pronounced ADHD symptoms when followed-up about six years later, compared to only 21 percent of those with at least one copy of the 7-repeat variant. There was also a trend toward better overall functioning among those with at least one copy of the 7-repeat variant at follow-up.
The MRI scans revealed that 7-repeat carriers with ADHD started out with the thinnest cortex areas important for controlling attention (right orbitofrontal and posterior parieto-occipital). The next thinnest were children with ADHD who did not have the 7-repeat version, followed by healthy children with the 7-repeat. Healthy children lacking the 7-repeat had the thickest cortex, but this did not appear to affect their IQ. However, the researchers note that other studies have found correlations between cortex thickness and certain measures of memory and intelligence.
In 7-r
'"/>
Contact: Jules Asher
NIMHpress@nih.gov
301-443-4536
NIH/National Institute of Mental Health
6-Aug-2007