Brain differences in babies may help explain why some autistic children are diagnosed later, research finds

Some children are identified as autistic by the age of three, while others aren’t diagnosed until they reach primary school or later. New research from scientists at Birkbeck, University of London, King's College London, and the University of Cambridge suggests these differences may be related to distinct patterns of early brain development, alongside differences in how and when autism is recognised.

The study followed more than 100 babies with an older autistic sibling, a group known to have a higher likelihood of developing autism than the general population. Researchers recorded the babies' brain activity while they looked at faces between six and ten months of age, before tracking their development until mid-childhood (ages 6 to 12).

The results show that both groups of babies processed faces differently during infancy. But the timing of these brain differences was different. In children diagnosed earlier, the differences appeared more rapidly after seeing a face. In children diagnosed later, they appeared more slowly.

The findings suggest that, for some children, a later manifestation of autism that results in a later autism diagnosis may relate to differences in early brain development rather than simply a delay in recognising autism.

Dr Tessel Bazelmans, lead author and Postdoctoral Researcher at Birkbeck, said: "Our findings add to growing evidence that autism is biologically diverse. Understanding these differences could help explain why some children show signs much earlier than others and, in the future, support more personalised approaches to assessment and support."

Professor Tony Charman, Emeritus Professor of Child Clinical Psychology at King’s College London, co-author of the study, commented: “There is increasing recognition that autism may sometimes not be clearly recognised and diagnosed until school-age or later. Up until now few biological signals have indicated why this might be. Our findings – alongside those of other recent studies – may help us better understand and respond to differences in the timing of recognition and diagnosis of autism.”

The research was conducted as part of the British Autism Study of Infant Siblings (BASIS), a long-running UK study following babies with an older autistic sibling from infancy into childhood.

In total, 22 children received an autism diagnosis by age three, 21 received a diagnosis later in childhood, and 59 did not receive an autism diagnosis during the study.

The researchers note that further research is needed to determine whether the findings apply to autistic children more broadly and to understand the biological mechanisms underlying these developmental differences.