The dictionary definition of "autism" is: a serious mental condition that makes it difficult for someone to react to and communicate with other people.
Most of the children I have met whose parents tell me are "autistic" seem completely normal. Some of them are a little reclusive or less willing to engage with others but, when the mood strikes, they can be very engaging.
I've come to believe that many "autistic" children--as well as "autistic" adults--are people who have been drugged over many years by prescription medications ostensibly to control "ADHD" but in reality are designed to sedate normally active children. As these children age, they are trained to think of themselves alone and to act disconnected to reality, but they are not physically different from the rest of society.
This is not to say that there truly are people who could genuinely be considered "autistic", but when one reads the lives of the saints one cannot escape the realization that many of them would be diagnosed as "autistic" if they were alive today. Instead of being nurtured they would have been medicated.