Research has shown that autism is caused by the brain functioning in an abnormal way. It is not caused by environmental factors such as poor parenting or emotional trauma. Autistic children nearly always start learning to talk late, if at all. Their progress with speech is often slow and the things they say are sometimes quite odd. They may have difficulty understanding what other people say, and may not seem to notice when people talk to them.
Autistic people lack awareness of other people.
They may not respond to other people, or may respond oddly. Autistic children rarely have much pretend play. Instead they tend to concentrate on the physical properties of things, so will like to look at things from odd angles, or line them up, or tap or spin things. They are not usually able to play interactively with other children. About a third of autistic people have severe learning disabilities, and another third have moderate learning disabilities.