Photo: moriza on flickr
Autism Spectrum Disorder (ASD) is known to be strongly influenced by genetics because it often runs in families, but which genes are at fault and how strong a role they play remains unclear.Now three studies of autistic children who had no family history of the condition suggest it could in some cases be caused by gene mutations which are not shared by either parent and occur for the first time in sperm or egg cells as they develop.
One paper emphasised that four times as many of the genetic alterations, known as “de novo” mutations, occur in the sperm than the egg and they become more common with age.
Researchers from the University of Washington analysed the DNA of children with autism and both of their parents in 209 families where the child was the only autistic person, as well as 50 unaffected brothers and sisters.
They found 248 “de novo” mutations, 60 of which they identified as the most likely to raise the risk of autism.
The finding that the sperm of older men carry more mutations backs up previous studies which suggest that older fathers are more likely to have autistic children, the authors of the study claimed.
A second paper singled out three new gened linked to autism, while the third focused on multiple mutations in genes linked to the development of the brain.
Collectively the three papers, each of which studied more than 150 families and was published in the Nature journal, suggest that the mutations which occur in the part of our DNA where proteins are programmed could play a role in the development of autism.
De novo mutations are fairly common in non-autistic people, meaning not every mutation raises the risk of the condition.
Only a small number of particular mutations occurred in more than one patient, suggesting that autism can most likely be caused by a range of different mutations in any of hundreds or even thousands of genes, experts said.
Dr Rosa Hoekstra, a genetics expert at the Open University, who was not involved in the research, said: “We already knew that there isn’t a ‘single gene for autism’, but these new research publications suggest that the underlying genetic mechanisms may be even more complex than previously thought.
“A striking result from these studies is the association between new genetic changes and paternal age. These findings are in line with earlier reports that older dads have a slightly increased risk of having a child with autism.”
Kevin Mitchell, of the Smurfit Institute of Genetics at Trinity College Dublin, said: “These studies reinforce the fact that autism is not one disorder – not clinically and not genetically either.
“Like intellectual disability or epilepsy or many other conditions, it can be caused by mutations in any of a very large number of genes. The ones we know about so far make up maybe 20-25% of cases – these new studies add to that list and also show how far we have to go to complete it.”
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