Autism should not be seen as a single condition with one unified cause, according to new research that highlights striking genetic and developmental differences between those diagnosed in early childhood and those diagnosed later in life.
An international team analysed behavioural and genetic data from more than 45,000 autistic people across Europe and the US. They found that children diagnosed before the age of six often had clear early social and communication difficulties that remained relatively stable over time, and showed distinct genetic profiles. By contrast, those diagnosed after the age of 10 were more likely to develop increasing social and behavioural challenges during adolescence, and faced higher risks 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, who led the study. “For the first time, we have found that earlier and later diagnosed autism have different underlying biological and developmental profiles.”
The researchers emphasised that they are not proposing a rigid split into separate diagnostic categories, noting that autism exists on a gradient and that many individuals fall between these groups. Still, the findings challenge the assumption that early-diagnosed individuals simply carry more autism-linked genetic variants. Instead, the genetic profiles of later-diagnosed autistic people overlapped more with those seen in ADHD, depression and PTSD.
The study, published in Nature, also showed differences in developmental milestones. Early-diagnosed children were more likely to walk late and have difficulties interpreting gestures, while later-diagnosed individuals often saw their difficulties intensify in adolescence and become more severe by late teenage years.
Autism diagnoses have increased sharply in recent decades – nearly 800% in the UK between 1998 and 2018 – due largely to broader criteria and greater awareness. Scientists have long debated whether the diverse ways autism manifests reflect distinct subgroups.
Prof Uta Frith, emeritus professor of cognitive development at University College London, said the new findings strengthen the case for recognising these distinctions: “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.”
