Autism should not be seen as a single condition with one underlying cause, according to new research that reveals clear biological and developmental differences between people diagnosed in early childhood and those diagnosed later.
The international study, drawing on genetic data from more than 45,000 autistic individuals in Europe and the US, found that children diagnosed before the age of six typically showed early social and behavioural difficulties that remained stable over time and were linked to a distinct genetic profile. In contrast, those diagnosed after the age of 10 were more likely to experience worsening social and behavioural challenges during adolescence and had a higher likelihood of co-occurring mental health 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 are not calling for autism to be split into separate diagnoses, noting that many people fall between the two groups. “It is a gradient,” said Warrier. “Many other factors also contribute to age of diagnosis, so applying these patterns to individuals risks false equivalency.”
Autism diagnoses have risen sharply, with an almost 800% increase recorded in the UK between 1998 and 2018, largely due to broader diagnostic criteria and greater awareness. While the condition is defined by challenges with social communication, sensory processing and restricted behaviours, its presentation varies widely, leading scientists to investigate whether subgroups with shared traits or developmental trajectories exist.
The new analysis, published in Nature, showed that the genetic profiles of early- and late-diagnosed autism only modestly overlap. Later-diagnosed autism had more in common, genetically, with ADHD and mental health conditions such as depression and PTSD than with early-diagnosed autism.
Children diagnosed early were more likely to walk later, have trouble interpreting gestures, and show communication challenges that remained consistent. Those diagnosed later often developed increasing difficulties during their teenage years and by late adolescence faced more severe social and behavioural challenges.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the research, said: “It makes me hopeful that even more subgroups will come to light, and each will find an appropriate diagnostic label. It is time to realise that ‘autism’ has become a ragbag of different conditions.”
