There is more and more evidence that ADHD is in the genes. The Neuropsychiatric Genetics Research Group at Trinity College in Dublin is studying how people inherit genes from their parents that predict development for ADHD, autism, depression and schizophrenia. These are real illnessess, with real biology. The hope is that genetic research findings will help people understand that mental health and medical health are one in the same, and remove the stigma associated with neurobehavioral conditions such as ADHD. The more we understand differences in the underlying causes of ADHD, the better we will be at treating it. Genes are not the whole picture, but it is clear they are a large component in our mental health as well as our physical.  

http://www.irishmedicalnews.ie/articles.asp?Category=news&ArticleID=18654