It seems to me that Autistic tendencies would be more prevalent in (or appearing as) IST types. The nature of the Autistic mind, to me at least, seems to be quite similar to an extreme use of Si.
I think that a lot of the supposed correlations between Autism and INTs came about due to the lack of popular understanding of Autistic processing. Many seem to have a notion of Autistic individuals being some sort of mysterious genius. While INTs may have some tendencies that are congruent to those of with a degree of Autism, I believe that in reality, the two are very different.
This taken from Wikipedia;
"- Compulsive behavior is intended and appears to follow rules, such as arranging objects in a certain way.
- Sameness is resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted.
- Ritualistic behavior involves the performance of daily activities the same way each time, such as an unvarying menu or dressing ritual. This is closely associated with sameness and an independent validation has suggested combining the two factors.
- Restricted behavior is limited in focus, interest, or activity, such as preoccupation with a single television program."
To me this sounds very much like an extreme use of the processes of Si + Ti (In no particular order).
Autism is defined by the lack (or inability) of development in "social" areas past a certain point, usually very young in a child's life. INTs don't necessarily lack development in these areas, they just develop them in a manner quite different than most of society. As a result of this, the majority (A.K.A. "Normal") of the population erroneously assumes that because of the INT's often very unique social interaction skills, they lack them alltogether. Being that the mentality is; if something doesn't funtion in exactly the same manner that everything else does, it doesn't function at all.
Just my observation.