Autism should not be viewed as a single condition with a unified cause, according to new research suggesting that people diagnosed in early childhood have different genetic profiles from those diagnosed later in life.
The international study, drawing on genetic data from more than 45,000 autistic individuals in Europe and the US, found that early-diagnosed cases, typically before age six, were more likely to show social and behavioural difficulties from early childhood that then remained stable. In contrast, those diagnosed later, usually after the age of 10, were more likely to experience increasing difficulties during adolescence and had a higher likelihood of additional mental health conditions such as depression.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier of Cambridge’s department of psychiatry, the senior author of the research. “For the first time, we have found that earlier and later diagnosed autism have different underlying biological and developmental profiles.”
Researchers stressed they are not calling for two separate diagnostic categories, warning that this could be unhelpful for individuals who fall between the two ends of the spectrum. “It is a gradient,” Warrier said. “There are also many other factors that contribute to age of diagnosis, so applying averages to individuals would be misleading.”
Autism diagnoses have risen sharply, with an almost 800% increase in the UK between 1998 and 2018, largely due to broader criteria and greater awareness. While autism is defined by challenges with social communication, sensory processing and restrictive behaviours, there is wide variation in how these manifest across individuals. Scientists have increasingly asked whether autism might cluster into subgroups with shared traits, making it easier to study.
The study, published in Nature, found that those diagnosed before six years were more likely to be slow to walk, have difficulty interpreting hand gestures, and experience early social and communication challenges that remained steady. Those diagnosed later, after the age of 10, were more likely to see their difficulties intensify through adolescence and often presented with more severe challenges by late teenage years.
Genetically, the differences were striking. Earlier diagnoses were linked with more traditional autism-related variants, while later diagnoses showed genetic profiles more closely aligned with ADHD, depression and PTSD, with only a modest overlap between the two groups.
Prof Uta Frith, emeritus professor of cognitive development at University College London, 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.”
