Of course they can coexist, but I'm not sure if that combination would make a lot of sence diagnosing. A friend of mine, the psychiatrists didn't know for a while if she is schizoid or asperger. They dx her with aspergers because it fitted better. But I still think there as some differences. I like to be by myself, but I'm clearly not schizoid. I enjoy some social situations, like sitting around with friends. So even that I've a lot in common with shizoid ppl there are still differences, but they are minor and the problem is that autism represents itself differently in each person. Also diagnosing personality disorders in autistic people is not that common and is usually just done in more severe cases, other than that they are mainly seen as "differential diagnosis".
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"I'm astounded by people who want to 'know' the universe when it's hard enough to find your way around Chinatown." - Woody Allen