Study points to new genetic risks for autism
A massive international study has started to unpick the "fine details" of why some people develop autism, researchers have said.
They looked at thousands of DNA samples from children with autism and their parents.
The results, in the journal Nature, linked 33 genes to the condition with many involved in brain development.
The National Autistic Society said we were still "a long way" from knowing the cause of autism.
The study suggested a number of different risk factors for the condition, according to the lead author of the paper Prof Joseph Buxbaum, from Icahn School of Medicine at Mount Sinai New York.
"The smoking gun is genetics - but there are quite a lot of different bullets in the gun," said Prof Buxbaum.
Autism is a life-long disorder that affects people's ability to socialise, and those on the autism spectrum can find it difficult to interact with other people.
The researchers assessed 15,480 DNA samples to determine the impact of mutations to the DNA that are passed from parent to child as well as those that spring up spontaneously.
The study expanded the number of genes linked to autism up to 33.
Seven genes were completely new while 11 had not been classed as true risk genes due to lack of data. Fifteen of the genes were already known to be risky.
It also indicated that small, rare genetic mutations in 107 genes can contribute to the risk of autism.
More than 5% of the autistic people in the study had these non-inherited loss-of-function gene mutations.
The study should help to improve understanding of some of the causes of autism, said Prof David Skuse, head of the social communication disorders team at Great Ormond Street Hospital in London, and a contributor to the report.
"Up until now we've really not been able to understand the mechanisms that lead to autism," he said. "This [study] is getting down to much finer detail."
Prof Skuse added that the study could start to help families understand autism.
The National Autistic Society (NAS) said there were many gaps in autism knowledge.
Carol Povey, director of the NAS Centre for Autism, said: "Autism is a highly complex story of genes not only interacting with other genes, but with non-genetic factors too.
"Research like this helps us to understand the genetics involved in certain forms of autism and opens up the possibility of whole families gaining a better understanding of a condition they may share," she said.
"However, we are still a long way from knowing what causes autism. What people with the condition, their families and carers need most of all, is access now to the right kind of support to be able to lead full lives," she added.