Autism should not be regarded as one condition with a single underlying cause, according to an international team of scientists who have identified distinct genetic differences between people diagnosed in early childhood and those diagnosed later in life.
The study, which analysed genetic data from more than 45,000 autistic people in Europe and the US, found that children diagnosed before the age of six often displayed early behavioural and social difficulties that remained relatively stable. By contrast, individuals diagnosed after the age of 10 were more likely to develop increasing social and behavioural challenges during adolescence and had a higher risk of co-occurring mental health conditions such as depression and PTSD.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier, from the University of Cambridge’s department of psychiatry and 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.”
While the researchers do not propose splitting autism into two formal diagnostic categories, they emphasise that autism exists on a gradient and that many people fall somewhere between the two identified profiles.
Autism diagnoses have risen sharply in recent decades, with an 800% increase in the UK between 1998 and 2018, largely due to broader diagnostic criteria and greater awareness. Although defined by difficulties in social communication, sensory processing and repetitive behaviours, the condition presents very differently between individuals.
The new analysis, published in Nature, showed only a modest genetic overlap between early- and late-diagnosed autism. Strikingly, the genetic profile of later-diagnosed individuals more closely resembled that of ADHD and other mental health conditions than that of children diagnosed early.
Children diagnosed before six were more likely to walk later, struggle with interpreting gestures and show early social communication difficulties that persisted but did not worsen. Those diagnosed after 10 tended to see a sharp rise in challenges during adolescence, often leading to more severe difficulties by late teenage years.
Commenting on the findings, Prof Uta Frith, emeritus professor of cognitive development at University College London, 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.”
