Autism should not be viewed as one condition with a single cause, according to new research showing that people diagnosed in early childhood often have different genetic profiles from those diagnosed later in life.
An international team analysed genetic data from more than 45,000 autistic people in Europe and the US, alongside behavioural data from long-term birth cohorts. They found that children diagnosed before the age of six were more likely to show early social and communication difficulties that remained relatively stable, and their genetic profiles carried more variants strongly linked to autism.
By contrast, those diagnosed after the age of 10 tended to experience worsening social and behavioural difficulties during adolescence and had a greater likelihood of developing conditions such as depression. Their average genetic profile overlapped more with ADHD and other mental health conditions, such as PTSD, than with early-diagnosed autism.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier of the University of Cambridge’s department of psychiatry, senior author of the study published in Nature. “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 a split into separate diagnostic categories, noting that autism exists on a spectrum with many overlapping cases. “It is a gradient,” Warrier said, adding that many other factors influence the age of diagnosis.
The study comes amid a sharp rise in autism diagnoses, with an 800% increase in the UK between 1998 and 2018, largely due to broader diagnostic criteria and growing awareness. While autism is defined by challenges in social communication, sensory processing and restrictive behaviours, the way these difficulties present varies enormously.
Prof Uta Frith, emeritus professor of cognitive development at University College London, said the findings reinforced the need to recognise subgroups within the spectrum. “It makes me hopeful that even more subgroups will come to light, and each will find an appropriate diagnostic label,” she said. “It is time to realise that ‘autism’ has become a ragbag of different conditions.”
