Can the results of studies involving subjects with High Functioning Autism automatically be applied to persons with Low Functioning Autism, to the 75-80% of persons with Autistic Disorder who are cognitively impaired?
In Brain Serotonin and Dopamine Transporter Bindings in Adults With High-Functioning Autism the authors are careful in the title to make it clear that their study subjects were persons with High Functioning Autism. The authors also specify that the subjects all have IQ's equal to or greater than 99 and are not representative of a typical sample of adults in the community. Yet the conclusion stated in the abstract is described as pertaining to all persons with "autism":
If it is important to identify the subjects of a study as having High Functioning Autism, as having average or greater IQ's, is it valid to generalize those results to other persons with Autism Disorder and intellectual disabilities?
Does it not seem reasonable that there might be different abnormalities involved in the neurological systems that result in some having High Functioning Autism as opposed to those with Autisic Disorder and cognitive impairment?
And why are more studies not done involving subjects with Low Functioning Autism?