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New research analyzing genetic and developmental data from more than 45,000 people suggests autism is not a single, uniform condition. Instead, timing of diagnosis—early childhood versus later childhood and adolescence—appears linked to distinct developmental trajectories and genetic signatures, with implications for diagnosis, support, and mental-health risk.
Two developmental pathways: early and later diagnoses
Researchers led by Xinhe Zhang at the University of Cambridge reviewed large datasets from the US, UK, Europe, and Australia, including genomic information on over 45,000 individuals. Their analysis indicates that children diagnosed with autism before age six typically show pronounced behavioral differences early on that tend to stabilize over time. By contrast, individuals first diagnosed after age ten are more likely to experience escalating behavioral challenges and develop secondary mental-health conditions such as depression or PTSD.
"We found that, on average, individuals diagnosed with autism earlier and later in life follow different developmental pathways, and surprisingly have different underlying genetic profiles," says Xinhe Zhang.
Autistic children have been found to have greater (red) and reduced (blue) neuron densities in different brain regions compared with non-autistic children. (Christensen et al., Autism Research, 2024)
Genetics, ADHD overlap, and what that means
One striking finding is that those diagnosed later were more likely to carry genetic signatures that overlap with attention-deficit/hyperactivity disorder (ADHD). That genetic intersection helps explain why clinicians and researchers sometimes struggle to separate ADHD and autism features in older children and adolescents.
"This paper reinforces yet again how complex autism is and how much genetics plays a role not just in a diagnosis but in the features of that diagnosis," Alycia Halladay, chief science officer at the Autism Science Foundation, told NBC News.
Gradients, not hard categories
The team emphasizes there is no clear-cut division between two “types” of autism. Rather than binary categories, genetic differences appear to create gradients of symptom patterns, strengths, and challenges. As Cambridge neurodevelopmental researcher Varun Warrier notes, "Genetic influences may alter which autism features emerge and when." Multiple subtypes likely exist, shaped by complex gene combinations and environmental factors.
Context, bias, and the role of social factors
Age at diagnosis is shaped by more than biology. Zhang and colleagues warn that access to healthcare, cultural norms, gender bias, stigma, ethnicity, and camouflaging behaviors all influence who receives a diagnosis and when. These social and systemic factors can make later-diagnosed autistic people more vulnerable to poor mental-health outcomes.
Recognizing different developmental pathways could improve personalized support. If clinicians understand how autism features can emerge across childhood and adolescence, they can tailor screening and interventions to reduce later mental-health risks.
Implications for research and care
The study points to several next steps: mapping how specific gene combinations interact with social environments, refining diagnostic tools to account for later-emerging autism presentations, and designing targeted supports for those diagnosed at different ages. Understanding the biology behind timing of diagnosis could help clinicians spot under-recognized autism presentations and prevent secondary psychiatric conditions.
In short, autism is complex and heterogeneous. Better genetic and developmental models—combined with attention to social determinants—offer a path toward more accurate recognition and individualized care for autistic people across the lifespan.
Source: sciencealert
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