Autism should not be understood as a single condition with one underlying cause, according to a major new study that reveals striking differences between people diagnosed in early childhood and those who receive a diagnosis later in life.
The international research project, which examined genetic and behavioural data from more than 45,000 autistic people across Europe and the United States, has found that age of diagnosis strongly correlates with differing genetic profiles and developmental pathways.
Children diagnosed before the age of six were typically identified because of early-emerging social and communication challenges. These children often showed delayed walking, difficulty interpreting gestures, and marked differences in social interaction that became apparent very early on. However, their difficulties tended to remain relatively stable over time rather than worsening. Genetic analysis revealed that this group carried a higher load of gene variants strongly associated with autism, suggesting that their diagnosis reflects a more biologically rooted developmental pathway.
By contrast, those diagnosed with autism after the age of 10 often had different trajectories. Their social and behavioural difficulties tended to intensify during adolescence, a stage of life when social demands increase sharply. This later-diagnosed group also had a stronger genetic overlap with conditions such as ADHD, depression, and post-traumatic stress disorder. Many experienced co-occurring mental health issues, which may complicate or even mask their autistic traits until later in development.
Dr Varun Warrier, senior author of the study from the University of Cambridge’s Department of Psychiatry, explained: “The term ‘autism’ likely describes multiple conditions. For the first time, we have evidence that earlier- and later-diagnosed autism are associated with distinct biological and developmental profiles.”
Importantly, the researchers stressed that they are not calling for autism to be split into separate diagnostic categories. The differences observed are best understood as points along a spectrum rather than entirely distinct disorders. “It is a gradient,” said Warrier. “When you move from group averages to the individual level, there is enormous variability, so a rigid division would not reflect reality.”
The study, published in Nature, analysed both behavioural data from four long-term birth cohorts and genetic data from large-scale genomic studies. It challenges long-held assumptions that early-diagnosed individuals simply represent more “severe” cases of autism. Instead, the findings show that the underlying genetics and developmental patterns of early and late diagnoses are only modestly overlapping, suggesting they may stem from different biological processes.
This research comes amid a dramatic rise in autism diagnoses worldwide. In the UK alone, diagnoses increased by nearly 800% between 1998 and 2018. Experts attribute much of this growth to expanded diagnostic criteria, heightened awareness, and better recognition of autism in individuals who might previously have been overlooked—particularly women, girls, and those with subtler traits.
The findings add weight to the idea that autism is not a single unified condition but rather a collection of related neurodevelopmental differences. Scientists hope that identifying subgroups with more specific genetic and developmental profiles will make it easier to design tailored support strategies and, in the long run, more personalised approaches to intervention.
Prof Uta Frith, emeritus professor of cognitive development at University College London, who was not involved in the study, noted: “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.”
The research highlights a future in which autism may be understood less as a single umbrella term and more as a family of related conditions with overlapping features but distinct causes. For autistic people and their families, this could one day translate into more accurate diagnoses, better-targeted support, and a deeper understanding of the extraordinary diversity within the spectrum.
