Autism should not be seen as a single condition with one underlying cause, scientists say, after research revealed striking genetic and developmental differences between those diagnosed early in life and those diagnosed later.
An international team analysed genetic data from more than 45,000 autistic people across Europe and the US, alongside behavioural data from birth cohorts, and found two broad diagnostic patterns. Children diagnosed before the age of six typically showed early-emerging social and communication difficulties that remained stable over time. By contrast, individuals diagnosed later – often after the age of 10 – tended 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, from the University of Cambridge’s department of psychiatry, who led the research. “For the first time, we have found that earlier- and later-diagnosed autism have different underlying biological and developmental profiles.”
The study, published in Nature, showed only modest genetic overlap between early- and late-diagnosed autism. Those diagnosed earlier carried more autism-linked genetic variants, while the genetic profiles of later-diagnosed individuals were closer to those associated with ADHD and mental health conditions such as depression and PTSD.
Children diagnosed before six were more likely to have delayed walking, struggle with interpreting hand gestures, and display social and communication challenges that persisted but did not worsen significantly. Those diagnosed later typically saw difficulties intensify during adolescence and presented with more severe challenges by their teenage years.
Warrier stressed that the findings do not imply a need for new diagnostic categories, noting that many people fall between the two groups: “It is a gradient … the moment you go from averages to individuals, it’s false equivalency.”
Autism diagnoses have risen sharply in recent decades, with an almost 800% increase in the UK between 1998 and 2018, largely due to expanded criteria and greater awareness. Experts say the new results support a shift toward recognising subgroups within the spectrum.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the study, welcomed the findings: “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.”
