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In my opinion autism is to children what schizophrenia is to adults. There's lots of supporting evidence, but no proof.

Auditory hallucinations in schizophrenics take the form of "hearing voices". The voices tell schizophrenics horrible threatening things. The symptoms of autism include failure to obtain language skills and failure to interact with others. So hearing voices would be impossible for someone who never achieved verbal communication. Further, communicating any other form of hallucination to anyone would be impossible for anyone who has no means of relating to or communicating with other people.

Autistic kids have brains which fail to develop normally. There are clues about why.