Autism should not be regarded as a single condition with a unified cause, according to new research showing that those diagnosed in early childhood typically have a different genetic profile from those diagnosed later.
The international study, drawing on 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 show behavioural and social difficulties from an early age, which remained relatively stable over time. Those diagnosed after the age of 10, however, were more likely to develop increasing difficulties during adolescence and were also more prone to mental health conditions such as depression.
“The term ‘autism’ likely describes multiple conditions,” said Dr Varun Warrier of the University of Cambridge, 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 researchers emphasised that they are not calling for two separate diagnostic categories, warning that this could be unhelpful since many people fall somewhere in between. “It is a gradient,” Warrier explained, noting that multiple factors influence the age of diagnosis.
The findings, published in Nature, come as autism diagnoses continue to rise sharply. Between 1998 and 2018, diagnoses in the UK increased by nearly 800%, largely due to broader diagnostic criteria and greater awareness. While autism is characterised by difficulties with social communication, sensory processing and restricted behaviours, the way these traits present can vary enormously.
The study combined behavioural data from four birth cohorts of up to 188 children with genetic data from more than 45,000 participants. Earlier diagnoses were linked to slower motor development, such as delayed walking, and early difficulties with communication, including interpreting gestures. Later diagnoses were associated with worsening social and behavioural problems during adolescence, and a genetic profile closer to that of ADHD, depression and PTSD than to early-diagnosed autism.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the research, 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.”
