Moreover, there's no one type of autism. There's no one treatment to help a child with autism -- no pill, no cure.
The cause is still a mystery, but one that scientists have been unraveling more in recent years.
So what is autism? Autism falls under an umbrella of disorders called "pervasive developmental disorders" (PDD) or autistic spectrum disorders (ASD).
"Autism spans a range of symptoms ...a range of degrees of symptoms so that one child with autism, or an autism spectrum disorder can be very different from another child," says Stone from Vanderbilt University's Kennedy Center for Research on Human Development.
According to the U.S. Centers for Disease Control and Prevention, 1 in 166 children is born with autism. Boys outnumber girls 4 to 1.
Most experts, doctors, therapists and researchers believe children are born with ASD, a brain disorder that leads to difficulties in social interaction, communication and behavior. Parents are experts, too, because they live with autism every day, for the rest of their lives.
Chicago speech therapist Sharon Rosenbloom, also the mother of 18-year-old son Joey with autism, puts it this way: "People with autism do not experience the world as others do."
If you don't have a child with autism, it may be difficult to imagine.
A 12-minute video, posted on the Web site of organization Autism Speaks will give you a glimpse into that world.
One mother describes her situation: "I didn't choose this. I was drafted. I have an autistic child."
Other mothers describe how people with "typical" children don't understand what families with autism go through.
"They have no idea," says another mother in the video. Another says she knows she can't live forever, but fears "what happens when I'm not here?"
Researchers have broken pervasive developmental disorders or autism spectrum disorders into five categories.
