These 'point mutations' are more likely to occur in sperm as men age, and the research, published in the journal Nature, fits in with previous work showing that older men are more likely to father children with the disorder. Everyone has point mutations in their DNA and most are harmless, but where they occur in important genes they can cause problems.
'These results confirm that it's not the size of the genetic anomaly that confers risk, but its location — specifically in biochemical pathways involved in brain development and neural connections', said Dr Thomas Insel, director of the National Institute of Mental Health in the US, which funded the work.
Despite the research highlighting the importance of non-inherited genes, three of the four mutations discussed in the paper were identified after gene sequencing of 549 families where both parents and the child tested were autistic. The mutations may increase a carrier's risk of developing autism by five to 20 times.
The study is published alongside two other studies investigating the role of point mutations in autism. Professor Joseph Buxbaum from the Mount Sinai School of Medicine in New York, and co-author of one of the studies, told Reuters that the three studies combined suggested that in total between 600 and 1,200 genes may contribute to the likelihood of whether people develop the condition.
One of the three studies, led by Dr Evan Eichler at the University of Washington in Seattle in the US, showed that the point mutations were four times more likely to occur in sperm cells rather than in egg cells. Dr Eichler told Reuters that the frequency of these genetic glitches developing is 'primarily driven by dad's age. That makes sense. As you get older, there are more and more chances for problems'.
The UK's National Autistic Society describes autism as 'a developmental disability affecting how a person communicates with, and relates to, other people and the world around them'. It encompasses a spectrum of disorders and people with autism range from those with a severe inability to communicate to those with Asperger's syndrome, a milder form.
Autism is a complex condition and the factors that may cause it have yet to be understood. 'Prior to the advent of new DNA sequencing technology, we were largely wandering in the dark searching for autism genes', said Professor Matthew State, of Yale School of Medicine and a co-author of one the Nature papers. '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'.