Lisa Bond spent years trying to understand why her son, Joshua, wouldn't make eye contact, threw fits when she tried to change his socks, and had so much trouble learning to speak.
It turns out Joshua, now 14, is missing a small chunk of DNA on chromosome 16 - a deletion so profound it impaired his neurodevelopment, causing autism and serious language and learning disabilities.
For Lisa, the genetic revelation is a huge relief. "Knowing just makes it so much easier to cope," she says.
For Dr. Stephen Scherer, at Toronto's Hospital for Sick Children, it is part of a "paradigm shift" in understanding the causes of the baffling disorder that affects almost one in 100 children.
Scherer and his colleagues have just released the world's largest genetic study of autism. They scanned the DNA of Joshua and 995 other children with the disorder from Canada, the United States and Europe.
The results, published in the journal Nature this week, show that individuals with autism have almost 20 per more gene deletions and duplicates than normal. Dozens of new "autism risk genes" were also uncovered.