Autism may not be a single condition with one underlying cause, according to new research that shows early and later diagnoses are linked to distinct genetic profiles and developmental pathways.
The international study, involving genetic data from more than 45,000 autistic people in Europe and the US, found that those diagnosed before the age of six were more likely to display early social and behavioural difficulties that remained stable over time. By contrast, those diagnosed later, often after the age of 10, were more likely to develop increasing difficulties during adolescence and had a higher likelihood of co-occurring conditions such as depression.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier of Cambridge’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.”
While the researchers stress they are not calling for a split into two diagnostic categories, they argue that autism should be seen as a gradient, influenced by multiple genetic and environmental factors.
The findings come amid a surge in diagnoses worldwide. In the UK, cases rose nearly 800% between 1998 and 2018, largely due to broader diagnostic criteria and growing recognition of the condition. Although autism is defined by challenges in communication, sensory processing and repetitive behaviours, the ways these manifest vary greatly among individuals. Scientists have long debated whether autism encompasses subgroups with distinct traits.
The latest analysis, published in Nature, showed that the genetic profiles of early- and late-diagnosed autistic people overlap only modestly. Later-diagnosed autism had stronger genetic similarities to ADHD and mental health conditions such as depression and PTSD than to early-diagnosed autism.
Children diagnosed before six were more likely to show delayed walking, difficulty interpreting hand gestures, and early but steady social challenges. Those diagnosed after 10 often experienced worsening difficulties through adolescence, eventually presenting with more severe issues.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the study, 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.”
