Autism is a spectrum and there is no clear cut between a perfectly neurotypical person and a profoundly disabled. You can measure number of autistic traits in general population and see that there are differences between groups, look e.g. here:

- The Autism Spectrum Quotient (AQ): evidence from Asperger Syndrome / high-functioning autism, males and females, scientists and mathematicians (https://link.springer.com/article/10.1023%2FA%3A100565341147...)

There is no a single paper proving that HFA is a binary condition, and many hints that it isn't.

(BTW: I dived into this topic some time ago, with already linked here http://crastina.se/autistic-traits-science-and-the-nerd-ster...)