Autism should not be regarded as a single condition with one underlying cause, according to new research showing clear biological differences between people diagnosed in early childhood and those diagnosed later in life.
The international study, published in Nature and based on genetic data from more than 45,000 autistic people in Europe and the US, found that those diagnosed before the age of six tended to have distinctive genetic profiles and early-emerging social and communication difficulties that remained relatively stable over time. By contrast, those diagnosed after the age of 10 were more likely to develop increasing behavioural and social challenges during adolescence and faced a higher risk of co-occurring conditions such as depression.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier of Cambridge University’s department of psychiatry, senior author of the study. “For the first time, we have found that earlier and later diagnosed autism have different underlying biological and developmental profiles.”
The researchers stressed they were not calling for autism to be split into two diagnostic categories, noting that many individuals fall between these profiles. Instead, they suggest that autism exists along a spectrum influenced by a range of genetic and developmental factors.
Autism diagnoses have risen sharply in recent decades, with UK figures showing an almost 800% increase between 1998 and 2018. Much of this rise has been attributed to broader diagnostic criteria and greater awareness. While all autistic people experience challenges with social communication, sensory processing, and restrictive behaviours, the ways these traits appear can vary dramatically.
The analysis showed that early-diagnosed individuals were more likely to have developmental delays, such as learning to walk later or struggling to interpret gestures. Later-diagnosed individuals tended to see difficulties escalate in adolescence and, by late teenage years, often experienced more severe challenges overall.
Genetic data also revealed that the average profile of those diagnosed later overlapped more closely with attention deficit hyperactivity disorder (ADHD), depression and post-traumatic stress disorder (PTSD) than with early-diagnosed autism.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the research, said the findings mark an important step forward. “It makes me hopeful that even more subgroups will come to light, and each will find an appropriate diagnostic label,” she said. “It is time to realise that ‘autism’ has become a ragbag of different conditions.”
