There are many forms, and degrees of autism. Two of which are classic autism and autistic syndrome. Classic autism is the more severe of the two. It can include lack of communication and even self-injurious behaviors. This form of autism is usually noticeable within the first few months of life.
Autistic syndrome is harder to notice and can go undetected for the first two years.
These children do not present symptoms that most doctors would find abnormal. Up until the age of onset these children can appear normal. Suddenly they seem to cease to progress or even regress. With a wider definition of autism more cases have come to doctors attention and statistics now show up to 20 per 10,000 births. Autism has been linked to the immune system and is now considered an autoimmune disorder.