A new international study led by researchers at the University of Cambridge has found that children diagnosed with autism early in life have different genetic and developmental profiles compared to those diagnosed later in childhood or adolescence. The findings, published in Nature, challenge long-held assumptions that autism represents a single condition with one common cause.
The research team, based in Cambridge’s Department of Psychiatry, analysed behavioural data from children in the UK and Australia and genetic information from more than 45,000 autistic people across Europe and the United States. Their results suggest that early- and late-diagnosed autistic individuals follow distinct developmental paths shaped by genetics as well as environment.
Children typically diagnosed before the age of six were more likely to show social and communication challenges early in childhood. In contrast, those diagnosed later often experienced growing social and behavioural difficulties during adolescence, along with higher rates of mental health conditions such as ADHD, depression, and PTSD.
By comparing genetic data, scientists discovered that the genetic makeup linked to later-diagnosed autism overlaps more closely with traits seen in ADHD and certain psychiatric conditions than with autism diagnosed in early childhood. While social factors—such as a lack of early support or experiences like bullying—may also play a role, the study indicates that genetics significantly influence when and how autistic traits appear.
Lead author Xinhe Zhang explained that the timing of an autism diagnosis may tell us more than previously thought. “Our findings show that early- and late-diagnosed autism differ not only in development but also in underlying genetics,” Zhang said. “This goes beyond access to healthcare or diagnostic awareness.”
Senior author Dr Varun Warrier emphasised that the results suggest autism is not one unified condition. “The term ‘autism’ likely describes multiple conditions with different biological origins,” he said. “This new understanding could guide how we recognise and support autistic people across all ages.”
The researchers found that polygenic factors—thousands of tiny variations in DNA that influence traits—accounted for around 11% of the differences in age at diagnosis. Some genetic factors, they say, may make autism-related traits visible from an early age, leading to earlier diagnoses. Others may shape how and when certain features emerge, causing some children’s difficulties to surface only later.
The Cambridge team believes these insights could transform both research and support for autistic individuals. Understanding how autism features develop not just in early childhood but throughout adolescence, they say, is key to ensuring timely recognition, diagnosis, and care across Cambridgeshire, the UK, and beyond.