My nephew has it, but my nephew also has a diet that is consistant to a sewer.
I think there are underlying issues which dr's cannot explain or figure out so they give it a fancy title like ADD.
There was no ADD when I was a kid in the 60's, Food was cleaner, the air was cleaner and there were just less chemicals everywhere.
They are doing studies now where people with ADD and et are being checked for heavy metal toxictiy and most kids with ADD have a high rate or lead, mercury and amonia in there systems.