This article on ADHD talks about research from Bath University in the UK.
Essentially it says
- Mental health risk higher in ADHD alone > Mental Health risk in Autism alone
- The risk is higher when there are co-morbidities (ie: Autism+ADHD)
Research confirms what many us have already felt and known about comorbidity of Autism+ADHD. The net effect is not a simple sum, but exponential.