A genetic "signature" of autism in babies as young as 12 months has been identified for the first time, an international conference is to be told.

A simple blood test is now being developed and may be available in one to two years, Professor Eric Courchesne will tell the Asia Pacific Autism conference in Adelaide on Thursday.

"This discovery really changes the landscape of our understanding of causes and effective treatments," says the director of the Autism Centre of Excellence at the University of California in San Diego.

"This is going to lead to much better treatments at a much earlier stage and a large percentage of children having an excellent outcome."

He said the several gene networks that are a common thread in autism have been identified for the first time.

"During the fourth, fifth and sixth months of pregnancy, they disrupt the production of brain cells, producing too many or in some cases too few, and how the cells are organised and connected," he said.

"We've also identified four gene networks that are a `biological signature' of autism in babies as young as 12 months.

"A blood screening test is being developed.

"At this stage it's looking very promising that the blood screening test will have high accuracy, specificity and sensitivity for children at risk of autism."

Professor Courchesne and his research partner Dr Tiziano Pramparo and their team have spent the past six years on this specific piece of work.

They scanned the brains and analysed the blood of more than 600 babies and toddlers aged from 12 months to four years.

"People have been looking at individual genes. What we've found is that it's how these genes combine in networks and how these networks disrupt brain growth that is a common pathway in autism."