Autism vs MR. Mr is a reflection of compromised intellectual skills which can be measured and categorized. I may also be seen in any medical, physical and psychological states. Autism, by contrast, is a psychological/biological psychological characterized by an inability to form relationships and relate. To the outside world. Autism means "preoccupation with the self". It may or may not effect intellect.
Different diagnoses. Some think that part of the rise in autism incidence is " diagnosis substitution", with autism as the primary diagnosis. Depending on the study, 35-65% of people with autism also have intellectual disability. Conversely, the lower the iq in those with id, the greater the chance of autistic behaviors. The two are categorical diagnoses with different criteria.
Different disorders. Many with autism also have mental retardation, but they are different disorders, and neither has anything to do with ses--although it is true that some "prefer" to think of their child as having autism rather than mr. Mr--now called intellectual disability--describes brain function much lower than age; autism describes impaired social interactions & language plus odd behaviors.