Autism should not be seen as a single condition with a single cause, according to new research that found striking differences between people diagnosed in early childhood and those diagnosed later in life.
An international study drawing on genetic data from more than 45,000 autistic individuals in Europe and the US found that early-diagnosed autism, typically before the age of six, was linked to distinct genetic profiles compared with those diagnosed after the age of 10.
Children diagnosed earlier were more likely to show behavioural and social communication difficulties from a young age, which then remained relatively stable. By contrast, those diagnosed later often developed increasing social and behavioural challenges in adolescence and had a greater likelihood of also experiencing conditions such as depression.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier, from the University of Cambridge’s department of psychiatry, who led the study. “For the first time, we have found that earlier and later diagnosed autism have different underlying biological and developmental profiles.”
The researchers emphasised they were not calling for autism to be split into two categories, noting that the differences represent a gradient and that many individuals fall in between.
The findings come as autism diagnoses have risen sharply, with an almost 800% increase in the UK between 1998 and 2018, largely due to broader diagnostic criteria and greater awareness. While autism is defined by challenges with social communication, sensory processing and restrictive behaviours, the way these difficulties present varies widely. Scientists have been exploring whether subgroups exist that could help refine understanding and treatment.
The analysis, published in Nature, showed that the genetic profiles of later-diagnosed autism overlapped more closely with those linked to ADHD and certain mental health conditions, including depression and PTSD, than with early-diagnosed autism.
Children diagnosed early were more likely to have delayed motor development, such as slower walking, and difficulty interpreting hand gestures, while their social and communication difficulties tended to appear early but remain stable. Those diagnosed later often experienced worsening difficulties during adolescence and, by late adolescence, showed more severe 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.”
