Professor Philip Shaw discusses similarities between ADHD, oppositional defiant disorder, and conduct disorder. The boundary between these disorders is somewhat unclear.

There are certain disorders that are so comorbid with ADHD that people have asked, are they a subtype of ADHD? A good example of this is oppositional defiant disorder and conduct disorder. Oppositional defiant disorder just means that a kid, to an extreme degree, will meet all requests with a very adamant 'no' and will do nothing they are asked, and conduct disorder is much more extreme. The kid actually does things that harm other people. And there is a high association between them, and some people have wondered if this means that there is a subtype of ADHD with oppositional defiant disorder or conduct disorder, because there are also a lot of kids with ADHD who do not have this. Probably more than half do not show these behavioral problems. So, the reason as to why there is an overlap – I am really not sure. There may well be that it’s a distinct disorder with distinct genetic factors; there is some evidence for that. It may well be just that if one part of the brain is compromised, say the frontal lobes, that is going to manifest itself in a lot of ways. The brain is almost certainly organized like a network. If you take out an important part of the brain, or if its maturation is delayed, that’s going to have downstream effects across the board in attention, in the way someone experiences and expresses their emotions, and their thought, so it could well be that the part of the brain that is most delayed in ADHD is also a pivotal part of the network systems of the brain that control emotion and other aspects of behavior.

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