The study was conducted as part of Europe’s IMAGEN Project, a comprehensive effort to understand the brain. The abstract indicates a strong phenotype link between ADHD and Conduct Disorder.
It’s unclear from the abstract, whether or not the subjects were on medication, but it’s likely they were. I’d like to see a study of diagnosed children BEFORE they were placed on pharmaceuticals. The authors appear to deduce a genetic component that has similar to both conditions. One wonders, however, if medication might not also cause epigenetic effects which can lead to the same set of results.