Most researchers are absolutely convinced that the cause is biological rather than psychological. Parents who do fit the description of the supposedly pathogenic parent almost invariably have normal, non-autistic children. With very few exceptions, the siblings of autistic children are normal. There is a consistent ratio of three or four boys to one girl. Virtually all cases of twins reported in the literature have been identical, with both twins afflicted.
Autism can occur or be closely simulated in children with known organic brain damage.
The symptomatology is highly unique and specific. 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.