Parents often notice the first signs of autism in their children at around 12 to 18 months. Maybe a child isn’t making eye contact, or won’t smile when mom or dad walks in the door.

But a new study suggests there is evidence of autism in the brain even earlier—well before a child’s first birthday—and that the signs can be seen on a magnetic resonance imaging (MRI) scan. “We’re learning that there are biological changes that occur at [the time] or before the symptoms start to emerge,” says Geraldine Dawson, a clinical psychologist and autism researcher at Duke University who was not involved in the new work. “It’s the ability to detect autism at its very earliest stages that’s going to allow us to intervene before the full syndrome is manifest.”

For the study, published this week in Nature, researchers conducted MRI scans on 150 children three times: at six months old, one year and two years. Just over 100 of the children were at high risk because they had an older sibling diagnosed with autism. The faster growth rate of the surface areas of their brains correctly predicted eight times out of 10 which of the high-risk children would go on to be diagnosed with the condition.

Enlargement of the brain seemed to correlate with the arrival of symptoms, says Heather Hazlett, a psychologist at the University of North Carolina’s Carolina Institute for Developmental Disabilities (CIDD), and the paper’s lead author. Still, with only 100 at-risk children, the study is too small to be considered definitive—nor should doctors rush to use MRIs to diagnose autism, Hazlett says.

But if the study results are confirmed in future research, it could offer a new option for screening high-risk children before their symptoms become obvious—and possibly at a time when treatment will be most effective. The faster pattern of brain growth “is a potential biomarker that could be used to identify those infants who perhaps could benefit from early stimulation,” Dawson says. “This could help those children have the best outcomes.”

– Karen Weintraub

Read more: Autism Starts Months before Symptoms Appear, Study Shows

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