Autism should not be seen as a single condition with one cause, researchers have argued, after finding that those diagnosed in early childhood have different genetic and developmental profiles from those diagnosed later in life.
An international team analysed genetic data from more than 45,000 autistic people in Europe and the US. They found that children diagnosed before the age of six were more likely to display behavioural and social difficulties from an early stage that then remained relatively stable. By contrast, those diagnosed after the age of 10 were more likely to see challenges emerge or worsen in adolescence, and also showed higher rates of mental health conditions such as depression.
“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.”
The researchers stressed they are not calling for autism to be split into separate categories, since many people fall between these patterns. “It is a gradient,” Warrier said, noting that social and environmental factors also influence the age of diagnosis.
Rates of autism diagnosis have risen sharply in recent decades, with an 800% increase in the UK between 1998 and 2018, driven by broader diagnostic criteria and greater awareness. While autism is defined by difficulties with social communication, sensory processing and restrictive behaviours, the way these appear varies widely between individuals.
The new study, published in Nature, challenges assumptions that earlier diagnoses simply reflect more severe traits. Instead, the genetic analysis showed that early- and late-diagnosed autism differ significantly, with only modest overlap. The genetic profile of later-diagnosed autism appeared closer to that seen in ADHD, depression and PTSD.
Children diagnosed before age six were more likely to show delays in walking and difficulty interpreting gestures, with early but stable social and communication challenges. Those diagnosed after age 10 tended to see problems escalate during adolescence and faced more severe difficulties by their late teens.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the work, 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.”
