Why So Many Kids With Autism Are Diagnosed At Older Ages

Despite broad efforts in recent years to identify children with autism early, many continue to go undiagnosed for years. New research suggests that genetics may explain why.

Kids who receive an autism label earlier — generally before the age of 6 — have distinct genetic and developmental profiles compared to those who are diagnosed at older ages, according to findings published this month in the journal Nature.

Researchers analyzed longitudinal data from children with autism in the U.K. and Australia to assess whether the age of diagnosis was associated with different behavioral trajectories. They also evaluated genetic data from more than 45,000 individuals with autism in Europe and the U.S., looking at sets of thousands of variants that are responsible for certain traits.

“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,” said Xinhe Zhang, a researcher at the University of Cambridge who led the study.

Children diagnosed with autism earlier in life were more likely to have behavioral challenges and issues with social interaction from a young age, the study found.

By contrast, those diagnosed later often exhibited social and behavioral difficulties during adolescence, the findings indicated. They were also at increased risk for depression and other mental health conditions.

Meanwhile, the genetic data showed distinct profiles for those diagnosed earlier versus later with little overlap. In fact, the researchers said that the average genetic profile of individuals diagnosed later is more similar to those with ADHD and mental health conditions than children with autism who were diagnosed at younger ages.

“Our findings suggest that the timing of autism diagnosis reflects more than just differences in access to healthcare or awareness, important as these are,” Zhang said. “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 said that their findings have broad implications for how autism is viewed and studied and for how those with the condition are supported.

“The term ‘autism’ likely describes multiple conditions,” said Varun Warrier from the University of Cambridge, a senior author of the study. “Understanding how the features of autism emerge not just in early childhood but later in childhood and adolescence could help us (recognize), diagnose and support autistic people of all ages.”