As many as one in every 166 children in this country is diagnosed with autism, but medical researchers still know little about its cause.
As the number of autism cases continues to rise, doctors still don't know why.
A cause for the condition is so difficult to find.
It is a true medical mystery: the secrets of an autistic brain.
Wendy Stone with Vanderbilt Children's Hospital said, "There is no identified, single cause of autism that is universal for all children. And there may never be.
As with many mysteries of the mind, doctors point to genetics and environment as culprits. But it could be more complicated than that.
The newest research shows that there is something that a child is born with that allows outside factors to wreak havoc on their little brains.
More simply, these children are not necessarily born with autism, but they are born with the potential to develop it.
But what outside factors play a role?
Stone said, "Before we are born it's the mother's womb and placenta. After we are born, it's what we eat, it's what we breathe, what we drink. There are so many different things out there that it's hard to pinpoint exactly what it is."
Still, any parent of an autistic child will have theories. When Zack Couch's parents learned he had autism his mother began to change his diet, worried he was eating something that was causing him to get worse. Some families believe that a preservative in some childhood vaccines called Thiomersal, is causing autism in their children.
The CDC says there's still no scientific link.
Dr. Bob Davis with the Centers for Disease Control and Prevention said, "Now that we have data coming in there are no data to suggest that the Thiomersal in vaccines is linked to autism."
And what about the genetic link? Doctors at Vanderbilt are studying siblings of children with autism.
"They are at elevated risk for developing autism, even at birth we can start following these children and we can identify the very earliest signs."
Catching those early signs may help doctors get one step closer to solving the mystery. Thousands of parents are suing in federal court claiming Thimerosal caused their children's impaired social interaction.
The first case went to court today. If the parents of the autistic children prevail in court, they would be entitled to compensation from a multi-billion dollar trust fund.