Changes in brain development have been detected in autistic babies as young as six months old - half a year or more before parents typically begin to notice symptoms of the condition, researchers have found.

The results shed light on the fundamental differences in the brains of autistic children and could help lead to earlier detection and treatment, said co-author Geraldine Dawson, chief science officer at Autism Speaks, which helped fund the study in the American Journal of Psychiatry.

A lot of the kids in this study, they looked pretty good socially at six months. But by 12 months of age, it was almost as if someone had pulled the curtain down. 

Parents often begin to notice autistic symptoms at ages one or two, and children typically are not diagnosed until five. Many parents perceive their child's symptoms appeared suddenly, which helped contribute to the now-debunked idea that autism is caused by vaccines, said researcher Christine Wu Nordahl, from the University of California Davis MIND institute, who was not involved in the new report.

The new study suggests that changes in the brain's communication pathways may take place silently, long before children begin to exhibit tell-tale problems communicating and socialising, or exhibiting repetitive behaviours, Ms Dawson said. Other studies, such as an article in January in Current Biology, have detected differences in how the brain reacts in the eye gazes of autistic babies as young as six to 10 months.

Eventually, researchers hope to be able to find a pattern in these brain scans that could allow them to spot those high-risk babies likely to be autistic, and begin intensive behavioural therapy, which is most effective when it is begun early, Ms Dawson said.

Senior author Joseph Piven, director of the Carolina Institute for Developmental Disabilities, said: ''A lot of the kids in this study, they looked pretty good socially at six months. But by 12 months of age, it was almost as if someone had pulled the curtain down.''

In the study, researchers performed brain scans, using MRIs, of 92 babies with an older, autistic sibling. Studies show that younger siblings of one autistic child have a nearly 20 per cent risk of being diagnosed with the condition. Twenty-eight children went on to develop autism. When researchers looked at their scans, they saw differences in the way that these pathways developed, Mr Piven said.

Ms Nordahl called the study ''remarkable'' and a ''great first step''. But she noted that the absolute differences among the children are small. The findings need to be repeated by other researchers before doctors can begin to create a reliable early detection system.

The study has other limitations, said Charles Nelson, a professor of paediatrics and neuroscience at Harvard Medical School. The findings would be stronger if researchers compared them with those of a control group of normal-risk children, who do not come from families with other autistic children.

McClatchy-Tribune