There is still controversy over neurological differences in the brains of autistic people and the rest of the population. However, it does appear from evidence obtained through autopsies, MRI and PET scans that there are subtle cellular changes in the autistic brain. Intolerance to specific food substances. This means that they will be unable to get rid of amines and phenolic compounds once they no longer have any use for them. These then stay in their body and may cause adverse effects, even in the brain.
Treatment is dietary as well as epsom salts baths.
Deficits in the reticular activating system. An unfortunate interplay between psychogenic and neurodevelopmental factors. Structural cerebellar changes. This is not so much a supposed cause of autism as an assertion as to its nature. The basic idea of the hypothesis is that autistic people lack an awareness of other peoples' minds that typical people start developing at a relatively young age, i.e. the autistic person doesn't so readily develop theories about what is going on in other people's minds.