Autism should not be viewed as a single condition with one underlying cause, according to new research that found distinct genetic and developmental differences between people diagnosed in early childhood and those diagnosed later in life.
The international study, analysing genetic data from over 45,000 autistic people in Europe and the US, revealed that those diagnosed before the age of six often showed early social and communication difficulties that remained stable over time. In contrast, people diagnosed after the age of 10 were more likely to develop increasing behavioural challenges during adolescence and had a higher risk of mental health conditions such as depression.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier of Cambridge University’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.”
The findings, published in Nature, suggest that while autism is defined by social communication challenges, sensory processing differences and restrictive behaviours, there is wide variation in how these traits present. The study indicates that early- and late-diagnosed autism share only a modest genetic overlap. Later-diagnosed cases showed stronger similarities in their genetic profile to ADHD, depression and PTSD than to autism diagnosed in early childhood.
Children diagnosed earlier were more likely to have delayed walking, difficulty interpreting hand gestures and persistent social difficulties. Later-diagnosed individuals often saw their difficulties intensify during adolescence, ultimately presenting with more severe challenges by late teenage years.
Autism diagnoses have risen sharply in recent decades, increasing by nearly 800% in the UK between 1998 and 2018, largely due to broader diagnostic criteria and greater awareness. Scientists hope that identifying subgroups could make studying autism more precise and help tailor support.
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.”
