If you think of the human genome as a book, says Penn State University researcher Scott Selleck, it now appears that changes in whole words or paragraphs might play a bigger role in autism than typos in individual letters.
Up until now, much of the work on autism and other disorders has focused on so-called "snips" -- single nucleotide polymorphisms -- which represent places where single letters of the DNA alphabet differ from the sequences in typical people.
But in an April study in the journal Human Molecular Genetics, the head of the Department of Biochemistry and Molecular Biology at Penn State and his team found that duplications of whole sections of DNA are more common in people with autism.
The duplications were particularly noticeable in "hot spots" of the genome that are prone to such variations, he said.
While it's too early to know the precise significance of each of these duplicated segments, he said, it's clear that children with autism have more of these kinds of genetic changes.
"If you change a single letter [of DNA], it may not change the function of the gene that much. But if you have a duplication or deletion, it can change the function rather dramatically."
The Penn State team found that the more genetic duplications a person had, the more severe his autism symptoms were, especially in communication difficulties.
One other thing is clear: the duplications affect genes that influence many systems besides the brain. Autism is often accompanied by other problems, including immune system or gastrointestinal abnormalities. "I don't think autism is only caused by changes in genes that are exclusive to the nervous system, because developmental biology doesn't work that way," he said.
"The genes and signaling systems that govern the patterning of your hand also govern the patterning of your brain. Developmental biology doesn't worry about the brain separately."
The Penn State study, which also involved scientists from the University of California, Davis, the University of Minnesota, Temple University in Philadelphia and the University of Washington, also looked at how the copy number variants differed between people with autism and those with other developmental problems, such as intellectual disabilities or multiple congenital abnormalities.
In those people, there was a significant increase in deleted DNA segments as well as an even larger increase in duplications. The take home: Children with autism have less overall change in their DNA copy numbers than children with more severe developmental conditions.
Finally, for those eager to see quicker progress on autism research, the Penn State scientist emphasized how complex the genetic problem is. In an organism as simple as the fruit fly, he said, it takes a quarter of the insect's 15,000 genes to build the retina of its eye.
"How many genes do you think it's going to take to build a behavior like language or social sensibilities? We know the genetic target of autism is huge; hundreds to thousands of genes are involved.
"But no one assumed this would be easy. All the more reason to keep pressing hard."
Mark Roth: email@example.com, 412-263-1130 and on Twitter: @markomar.