Researchers have identified three more genes implicated in autism in a new study. This research effort also provided evidence to explain why it occurs more frequently among children of older parents.
Mutations in three genes called CHD8, SNC2A and KATNAL2 were found among children with so-called autism spectrum disorders (ASD), according to one of a trio of papers published in the journal Nature.
But many more faulty genes remain to be found and understanding how they do their disruptive work will be an even greater task, the authors said.
"We now have a good sense of the large number of genes involved in autism and have discovered about 10 percent of them," said Joseph Buxbaum, a professor of neuroscience at the Mount Sinai School of Medicine in New York.
"We need to study many more parents and their affected children if we are to uncover the genes important in ASD. As these genes are further characterised, this will lead to earlier diagnosis and novel drug development. This work is crucial for advancing autism treatment."
ASD describes a broad range of impairments in which an individual is unable or unwilling to communicate or interact with others, often cripplingly so.
Some patients have delays in their cognitive development, whereas others can have dazzling gifts in specific fields such as maths or music.
Previous research has found a strong, but poorly understood, inherited link to ASD.
But there are also many cases that occur in families where there is no known history of the disease.
Delving into this phenomenon of "sporadic" autism, a team from Yale University say they believe about 15 percent of cases occur in new gene mutations which occur at conception.
They are also more frequent in children born to older fathers, a finding that at least partially explains why there is an increased risk of autism in children of older parents.
But exactly how these mutations affect cerebral development is unclear.
The third paper, also probing "sporadic" autism, found that many of the new variants seemed to have no immediate connection with the disorder itself.
All three investigations were based on comparing the genome, or DNA code, between hundreds of individuals with ASD and those who do not have the disorder.
Once prohibitively expensive, gene sequencing has fallen dramatically in cost thanks to cheap computing, and this is proving a boon for fundamental research in health.
"Prior to the advent of new DNA sequencing technology, we were largely wandering in the dark searching for autism genes," said Yale researcher Matthew State.
"Now we are getting a clear view of the genetic landscape and finally have the tools in hand to find a large proportion of the many genes contributing to autism."