What is autism?

A brain disorder that makes it difficult to communicate or interact normally with others.

Scientists say they're not sure, possibly a combination of genetics and environment.

Twenty years ago, it was estimated at one in 2,000 children. By 2007, it was one in 150 children.

Scientists aren't sure how much is a genuine increase, and how much is due to changes in how autism is defined and diagnosed. The term used now is "autism spectrum disorder," which includes milder conditions such as Asperger syndrome.