By Hannah Millington

Copyright newsweek

People diagnosed with autism in early childhood may have genetic and developmental differences from those diagnosed in late childhood and onwards.

This is the finding of researchers from the University of Cambridge, who say the two different trajectories challenge long-held assumptions that autism is a single condition with a unified underlying cause.

Generally, it’s accepted that Autism’s cause is not currently known—or even if the neurodevelopmental condition has one—and a range of genetic factors are thought to play a role.

“But from a polygenic perspective, the prevailing hypothesis was that there is one polygenic factor—an autism polygenic factor,” study author Varun Warrier from Cambridge’s Department of Psychiatry explained to Newsweek.

“We show that this isn’t true, in that there are at least two different polygenic factors. Each of these factors are associated with several millions of genetic variants.”

Warrier said their research also challenges the assumption: “That later diagnosed autism is just ‘milder autism’. We show that this is not true. We show that later diagnosed autism is different, but not milder.”

Smiling child with backpack at school | Getty Images/Ridofranz

The finding could change how we view, diagnose and support people with autism, according to the team. Some 1 in 31 children and 1 in 45 adults in the U.S. have autism, a condition that means people’s brains work differently from others.

“The term ‘autism’ likely describes multiple conditions,” Warrier added in a statement. “For the first time, we have found that earlier and later diagnosed autism have different underlying biological and developmental profiles.”

“These findings provide further support for the hypothesis that the umbrella term ‘autism’ describes multiple phenomena with differing etiologies, developmental trajectories and correlations with mental health conditions,” the researchers wrote in their paper.

The team’s findings are based on analysis of behavioral data across childhood and adolescence from the U.K. and Australia and genetic data from more than 45,000 autistic individuals across Europe and the U.S.

They found children diagnosed as autistic earlier on in life (around before six) were more likely to show behavioral difficulties from early childhood, like problems with social interaction.

Those diagnosed later on in life, however, were more likely to experience social and behavioral difficulties during adolescence and an increased chance of mental health conditions like depression.

Looking at the genetic data, they discovered the underlying genetic profiles—an individual’s unique DNA pattern—differed between those diagnosed with autism earlier and later in life, with only a small overlap.

Notably, the average genetic profile of later-diagnosed autism was found to be closer to that of ADHD and mental health conditions like depression and post-traumatic stress disorder (PTSD) than it is to autism diagnosed in early childhood.

DNA structure in blue | Getty Images/TanyaJoy

The team acknowledged a lack of support and understanding in early childhood could also play a role in increased risk of mental health issues in the later-diagnosed group.

However, they believe the stronger genetic overlap between later diagnoses and certain psychiatric conditions suggests there may be some genetic factors that partly increase the risk of these mental health conditions at this stage.

“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,” said paper author and psychiatrist Xinhe Zhang in a statement.

The researchers found commonly heritable polygenic factors—that can shape particular traits—explain around 11 percent of the variation in age at autism diagnosis.

“An important next step will be to understand the complex interaction between genetics and social factors that lead to poorer mental health outcomes among later-diagnosed autistic individuals,” said Warrier.

The researchers say their findings suggest genetic and developmental variation contributes to when and how autistic traits manifest and why some individuals are diagnosed only later in life.

“Some of the genetic influences predispose people to show autistic traits from a very young age that may be more easily identified, leading to an earlier diagnosis,” added Warrier. “For others, genetic influences may alter which autism features emerge and when. Some of these children may have features that are not picked up by parents or caregivers until they cause significant distress in late childhood or adolescence.

“Understanding how the…