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According to scientists who analyzed genetic information from more than 45,000 autistic individuals in Europe and the US, autism should not be viewed as a single condition with one root cause.

The global research revealed that those diagnosed with autism at a young age, usually before six years old, often have a distinct genetic profile than those diagnosed at an older age.

Key Findings from the Study

• Early-diagnosed children were more likely to show behavioral difficulties from early childhood, including problems with social interaction, but remain consistent as they grow.
• Individuals diagnosed with autism later, often past age 10, were more likely to develop increasing behavioral and social challenges during teenage years and additionally had an higher likelihood of mental health disorders like depression.

"The label ‘autism’ probably describes multiple disorders," explained Dr Varun Warrier, senior author of the study. "Initially, we have found that earlier and late diagnosed autism have different underlying and developmental characteristics."

Not Two Groups, But a Spectrum

The experts do not recommending a shift to two identification categories, saying that this could be unhelpful for the numerous who are in between.

"It is a gradient," Warrier commented. "There are also numerous other factors that influence age of diagnosis, so the point you move from general trends to something that is applicable to an person, it's false equivalency."

Increasing Autism Identification Rates

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

Experts explain this is mainly because of a broadening of the assessment guidelines and increased awareness of the disorder.

Variability and Subgroups in the Condition

And, while autism is characterized by experiencing difficulties with social communication, sensory processing, and restrictive behaviors, there is significant variability in how these difficulties appear between individuals.

Scientists have been investigating whether the population forms subgroups, with common traits or trajectories, that could make studying autism more tractable.

Study Methodology and Genetic Findings

This recent study used behavioral information from four study groups and biological data from two extensive investigations, with over 45,000 individuals.

In the past, it was commonly assumed that those diagnosed earlier were usually those with more pronounced autistic features, supported by people carrying a higher proportion of autism-linked gene variants.

However, the latest research revealed a distinct pattern.

Distinct Biological Patterns and Developmental Trajectories

This examination revealed that the underlying genetic profiles differed between those diagnosed with autism earlier and later in life, with only a small similarity.

Their average genetic profile of later-diagnosed autism is more similar to that of ADHD, as well as to mental health conditions like anxiety and PTSD, than it is to autism identified in early childhood.

• Individuals identified prior to the age of six years were more likely to be slow to walk and have difficulty understanding hand gestures and tended to experience communication and social difficulties that appeared soon but remained consistent.
• Those identified past the age of 10 years were more likely to experience an increase in challenges in adolescence and, by older teenage years, displayed more severe difficulties.

"This gives me hope that additional categories will be identified, and each will find an appropriate diagnostic label," commented Prof Uta Frith, who was not involved in the research. "Now is the moment to realize that ‘autism’ has become a ragbag of various conditions."