Here, it’s important to keep diagnoses clear: there is schizoid personality disorder, schizophrenia, and schizo affective disorder. Laymen have a tendency to refer to a single mental disorder by all three mental health diagnoses, and they are quite in the wrong by doing so. Schizophrenia, or classic schizophrenia, is the type we all think about. Individuals who suffer from it typically hear voices, have auditory or visual hallucinations, and are told by disembodied voices to harm themselves or others. Schizo affective disorder is a milder form of schizophrenia, where the hallucinations are focused on just one task, one person or one situation that the affected person can’t seem to shake; it perseveres, like the broken record that constantly repeats itself. The patient is also tormented by a mood disorder, which can look like depression or bipolar disorder. Schizoid personality disorder resembles autism in that the affected person chooses to be alone, appears aloof and lacking in emotion where others are concerned; however, the person affected by schizoid personality disorder has a very rich internal fantasy world that he likes to escape to as often as possible because he views the real world as too difficult to live in.
There’s also schizotypal disorder, which is diagnosed when a person is desperate for social isolation. He needs to be as far from people as he can, and can’t develop a relationship because the fear and anxiety he feels is so overwhelming that it just feels “safer” to b alone. He might talk to himself a lot, or have very odd notions about what other people say and do.
A few decades back, several people who were diagnosed with schizoid personality disorder were actually misdiagnosed. It was later discovered that they had autism, because the defining characteristic of the schizoid disorder was proven not to exist in people with autism. Some were even misdiagnosed with schizotypal disorder as well!
While it’s possible that these two schizo disorders, or even schizophrenia, can be comorbid with autism, it’s highly unlikely because of the significantly low rate of occurrence of anything in the personality disorder or psychotic spectrum. The only things that might make a difference is if both autism and schizoid personality disorder runs in a family; both have shown to have some measure of genetic connection. However, in order to be diagnosed with both, the person with autism would also have to be really high functioning such that they can describe what they are thinking and feeling internally, and that’s just really too hard for most people with autism to do. Their thought processes don’t really jump into the realm of fantasy because they are very logical and literal in the way that they think.
Ergo, while the schizoid personality disorder and autism may have some familiar features, they are otherwise nothing alike, nor can they really exist in the same person. They are two different arching disorders which would be exceedingly difficult to cross. Statistically speaking, it’s much more probable to have autism than any schizoid disorder, even with family genetics and history factoring in.