That's my point.
Because we don't have a physiological or biological test for a disorder doesn't mean it doesn't exist.
Nobody would doubt Autism's existance because it's so debilitating but with the other autistic spectrum disorders this lack of physical diagnostic tends to make people think "excuse for bad parenting"
However there are physical clues. For example this is much more commonly seen in boys than girls and does tend to run in families (Personally I and my uncle sound as if we were/are sufferers)
There is also interesting work regarding a correlation between ADHD and low dopamine receptors
http://www.medpagetod...atrics/ADHD-ADD/15872 for example but google ADHD and dopamine and you'll see what I mean.
Remember too that Ritalin and other treatments are not downers but stimulants.
I rather suspect that we are on the verge of understanding ADHD and it's cousins ADHD=naughty children may soon sound as silly as treating someone with leeches