Autism should not be viewed as one unified condition with a single cause, according to new research that shows distinct genetic differences between those diagnosed in early childhood and those diagnosed later.
An international study of genetic data from more than 45,000 autistic people in Europe and the US found that children diagnosed before the age of six were more likely to display early social and behavioural difficulties that remained relatively stable over time. By contrast, those diagnosed after the age of 10 tended to experience worsening social and behavioural challenges during adolescence and were at greater risk of developing 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 findings, published in Nature, indicate that the genetic profiles of early- and later-diagnosed groups overlap only modestly. Those diagnosed later show genetic similarities to ADHD, depression and PTSD, whereas early-diagnosed individuals are more strongly associated with variants linked directly to autism.
Children diagnosed before six were more likely to be late walkers, have difficulty interpreting gestures, and present with stable social and communication difficulties. Those diagnosed after 10 often saw their difficulties intensify during adolescence, with more severe challenges by late teenage years.
The study does not recommend splitting autism into separate diagnostic categories, as many individuals fall along a spectrum. “It is a gradient,” Warrier explained. “The moment you go from averages to individuals, it’s false equivalency.”
Autism diagnoses have risen sharply in recent decades, with an 800% increase in the UK between 1998 and 2018, largely due to broader diagnostic criteria and greater awareness. Scientists have long debated whether autism encompasses subgroups with distinct traits, and this study strengthens the case for multiple biological pathways.
Prof Uta Frith, emeritus professor of cognitive development at University College London, welcomed the research. “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.”
