A consortium of hundreds of scientists said Wednesday they had uncovered dozens of previously unknown genetic mutations that contribute to autism in children.
Some of these rare DNA glitches are inherited from parents. But many, the researchers discovered, arise for the first time in the person with autism.
"This suggests that tiny genetic errors may occur during formation of the parents' eggs and sperm, and these variations are copied during creation of their child's DNA," said co-author Daniel Geschwind, a professor at the University of California at Los Angeles (UCLA).
Autism and related brain disorders affect up to 10 out of every 1,000 individuals.
Symptoms are life-long and can vary widely, but often include impaired social skills, repetitive behaviours, difficulty in expressing one's emotions, and an aversion to physical intimacy. There is no known cure.
Harnessing massive computing power spread across 60 institutes worldwide, researchers combed through the DNA of nearly 1,000 school-age kids with autism from the United States, Canada and Europe.
Over three years, they hunted for stretches of genetic code that were either abnormally absent or duplicated, and that might give rise to some of the condition's signature symptoms.
The results were compared to the genomes of some 1,300 children not suffering from the condition.
These missing or excess blocks of DNA showed up approximately 20 percent more frequently in the children with autism, according to the study, published in the British journal Nature.
The findings also confirm earlier reports from smaller samples that some youngsters carry so-called "private genetic mutations."
"Every child showed a different disturbance in a different gene," said Stanley Nelson, also at UCLA.
This uniqueness may make it more difficult to design drug therapies that work across a wide range of autistic spectrum disorders, the study said.
Despite the singular genetic profile, however, two categories of genes were affected more frequently than others: those coding for the neural cell development, and those involved in the signalling or "communication" between cells.
Many of these same genes are thought to play a role in other neuro-development disorders.
There may even be some overlap with conditions such as epilepsy and schizophrenia, the researchers said.
"These and other recent findings have very real potential to lead to the development of novel interventions and treatments for these disorder," said Louse Gallagher, a professor at Trinity College Dublin, one of the universities in the consortium.
The study's large sample size made it possible to pinpoint rare genetic variants that have gone detected in earlier studies.
Still, the findings only explain a small percentage of gene-caused autism, Nelson said.
"In order to identify all of autism's genetic causes, we need tens of thousands of families to volunteer their DNA samples for sequencing," he said.