Autism should not be regarded as one condition with a single underlying cause, scientists say, after new research found distinct genetic profiles among people diagnosed in early childhood compared with those diagnosed later in life.
The international study, involving genetic data from more than 45,000 autistic individuals in Europe and the US, revealed that children diagnosed before the age of six typically showed early and stable difficulties with social interaction and communication. By contrast, those diagnosed after the age of 10 were more likely to develop increasing social and 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.”
Researchers stressed they were not calling for autism to be split into separate diagnostic categories, warning this would be unhelpful for many individuals whose experiences lie between the two patterns.
Autism diagnoses have risen sharply in recent decades, with cases in the UK increasing nearly 800% between 1998 and 2018, driven largely by broader diagnostic criteria and greater recognition. While defined by challenges in social communication, sensory processing and restricted behaviours, autism presents with wide variability, prompting scientists to investigate whether subgroups exist with shared genetic and behavioural traits.
The new study, published in Nature, analysed behavioural data from four birth cohorts and genetic data from two major studies. Contrary to previous assumptions that earlier diagnoses reflected more severe autistic traits caused by a higher number of autism-linked gene variants, the findings showed significant genetic differences between the groups. The genetic profile of later-diagnosed autism overlapped more closely with ADHD, depression and PTSD than with autism diagnosed in early childhood.
Children diagnosed before six were more likely to have delays such as late walking and difficulty interpreting hand gestures, alongside persistent early-onset social and communication difficulties. Those diagnosed after 10 tended to experience worsening problems during adolescence, ultimately facing more severe challenges by late teenage years.
Prof Uta Frith, emeritus professor of cognitive development at University College London, said the research underscored the need for more nuanced understanding. “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.”
