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According to scientists who analyzed genetic information from over 45,000 autistic individuals across Europe and the US, autism must not be regarded as a unified condition with one root origin.

This international study revealed that those identified with autism early in childhood, usually prior to age six, often have a different biological makeup than those diagnosed at an older age.

Important Discoveries from the Study

• Early-diagnosed children were more likely to exhibit behavioral difficulties from a young age, such as difficulties in connecting with others, but stay stable over time.
• Individuals identified with autism at an older age, often after ten years old, were more likely to develop increasing social and behavioral challenges in teenage years and additionally showed an increased risk of psychological conditions like depression.

"The term ‘autism’ probably refers to multiple conditions," stated the lead researcher, senior author of the research. "For the first time, we have discovered that earlier and later diagnosed autism have distinct underlying and developmental profiles."

No Dual Groups, Rather a Gradient

The scientists do not recommending a shift to two identification categories, saying that this might be unhelpful for the many that fall somewhere in the middle.

"It is a gradient," Warrier commented. "Additionally, there are many other factors that contribute to when someone is diagnosed, so the point you go from general trends to something that is applicable to an person, it's false equivalency."

Increasing Autism Spectrum Diagnoses

The findings come at a time when autism identification has risen sharply, with a almost 800% increase in cases in the UK between 1998 and 2018.

Specialists say this is mainly because of a widening of the assessment guidelines and greater awareness of the disorder.

Variability and Categories in Autism

And, while autism is defined by experiencing challenges with interacting with others, sensory processing, and repetitive behaviors, there is significant diversity in how these challenges present between people.

Scientists have been investigating whether the group clusters into subgroups, with shared traits or trajectories, that could make studying autism more manageable.

Research Approach and Biological Findings

The latest study used observational data from several study groups and biological data from multiple extensive studies, with more than 45,000 individuals.

In the past, it was generally thought that those diagnosed earlier were usually those with more pronounced autistic traits, supported by people having a greater amount of autism-linked genetic differences.

Yet, the recent study uncovered a distinct pattern.

Different Biological Profiles and Behavioral Paths

The analysis found that the underlying genetic patterns differed between those diagnosed with autism earlier and later in life, with only a small overlap.

Their average biological pattern of later-diagnosed autism is closer to that of ADHD, as well as to psychological disorders like anxiety and PTSD, than it is to autism identified in early childhood.

• Individuals diagnosed before the age of six years were more likely to be slow to walk and have trouble understanding hand gestures and often show social and communication challenges that emerged soon but stayed stable.
• Individuals identified after the age of 10 years were more likely to experience an increase in challenges during teen years and, by late adolescence, displayed more severe difficulties.

"It makes me hopeful that additional categories will come to light, and every one will receive an appropriate identification," commented an expert in cognitive development, who was not involved in the research. "It is time to realize that ‘autism’ has become a mixed collection of different disorders."