Actually, yes, ADHD can be an additional diagnosis to one of the ASDs. A lot of the time, the ASD is misdiagnosed as being ADHD, but sometimes, there is a comorbid case of ADHD. The symptom overlap is what makes it hard to pick out what disorder is what.
In addition to my Asperger's, I have comorbid OCD. I have obsessive-compulsive symptoms that are from the Asperger's (like a need for routine and obsessive interest in topics), but I also have clear-cut clinical obsessions and compulsions. I also have panic attacks that come from both Asperger's and OCD fears.

-GatsbyLuvr1920-