They are both autism, they both involve the same traits, the major difference is severity of the these traits.
A person with Stage 4 tongue cancer has a very different experience and needs than a person with stage 0 tongue cancer but there is no widespread feeling that these two people have a totally separate condition.
There are people that are mildly depressed, and some that literally can't get out of bed except to try to commit suicide. We don't generally say they have two different conditions.
Why high functioning VS low functioning? Is this some sort of competition?
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Professionally Identified and joined WP August 26, 2013
DSM 5: Autism Spectrum Disorder, DSM IV: Aspergers Moderate Severity
“My autism is not a superpower. It also isn’t some kind of god-forsaken, endless fountain of suffering inflicted on my family. It’s just part of who I am as a person”. - Sara Luterman