[0xRolex]

Some has already be done, in 2012 I think a team from harvard found biological markers which were identicals in patients suffering from autism/bipolar disorder/schyzophrenia and adhd and since adhd is a group of symptoms which can be caused by every "real" disorded listed above we found the biological something you mention.

[modo_mario]

Do you perhaps still have this study around? I searched but could not find it and It sounds quite interesting to me.

[0xRolex]

It was referenced in the book "ADHD does not exist" from Richard Saul M.D, I'll look for the book to find some links