Healthcare (Commonwealth Union) – Scientists have found distinct genetic patterns associated with two main developmental paths that autistic children often follow. One pathway is connected to early diagnosis and communication issues that are seen in infancy, while the other is associated to later diagnosis, more pronounced social and behavioral challenges that occur during adolescence, and higher risks of conditions like ADHD, depression, and PTSD.
An international team led by scientists at the University of Cambridge has found that autism identified in early childhood shows a different genetic and developmental signature compared to autism diagnosed from late childhood onwards.
According to the researchers, these results overturn the long-standing belief that autism is a single condition driven by one underlying cause.
The study, published in Nature, combined behavioural data from children and adolescents in the UK and Australia with genetic information from more than 45,000 autistic individuals across major research cohorts in Europe and the United States.
The Cambridge team, based in the Department of Psychiatry, discovered that children diagnosed before the age of six were more likely to display behavioural challenges early on — including difficulties in social engagement and communication.
However, individuals who received an autism diagnosis later in life — during late childhood or adolescence — were more likely to face social and behavioural challenges in their teenage years. They also showed a higher risk of developing mental health conditions such as depression.
The researchers then compared genetic data with the age at which people were diagnosed. They discovered that the genetic patterns differed notably between those diagnosed early and those diagnosed later, with only limited overlap between the two groups.
Interestingly, the average genetic profile of people diagnosed later in life resembled that of individuals with ADHD and mental health conditions like depression and PTSD more closely than it did that of people diagnosed with autism in early childhood.
The study’s authors also noted that insufficient support during early development likely contributes to the higher rates of mental health problems seen in those diagnosed later — for instance, through increased exposure to bullying before receiving a diagnosis.
Even so, researchers emphasise that the stronger genetic similarity between later-diagnosed autism and certain psychiatric disorders indicates that shared genetic factors may partly explain the elevated risk of mental health conditions among people whose autism is identified later in life.
The lead author Xinhe Zhang from the University of Cambridge indicated that they discovered that, on average, individuals who were found to have autism earlier and later in life follow different developmental routes, and astonishingly have various underlying genetic profiles.
“Our findings suggest that the timing of autism diagnosis reflects more than just differences in access to healthcare or awareness, important as these are. However, it is important to note that these are average differences on a gradient, so earlier and later diagnosed autism are not valid diagnostic terms.”
The researchers examined “polygenic” influences — groups of thousands of genetic variants that together can affect certain traits. They discovered that these commonly inherited genetic factors account for roughly 11% of the differences in the age at which autism is diagnosed.
The senior author Dr. Varun Warrier from the University of Cambridge, Department of Psychiatry stated that “The label ‘autism’ probably covers several distinct conditions. He further indicated that this is the first evidence showing that autism diagnosed early in life and autism diagnosed later have distinct biological and developmental foundations.
Dr. Warrier indicated that their next challenge is to untangle how genetics and social experiences interact to produce poorer mental health outcomes in autistic individuals who receive a diagnosis later in life.
According to the researchers, these findings have important implications for how autism is understood, researched, and supported. The results indicate that genetic and developmental differences influence both the timing and expression of autistic traits — and may help explain why some people are not diagnosed until later in life.
