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Based on scientists who studied biological information from over 45,000 people with autism across Europe and the US, the condition must not be regarded as a single condition with one underlying origin.

The international study revealed that those identified with autism at a young age, typically prior to age six, often display a distinct genetic profile than those diagnosed at an older age.

Key Findings from the Study

• Early-diagnosed children were more likely to show social challenges from a young age, such as difficulties in connecting with others, but remain consistent as they grow.
• Those identified with autism later, often after ten years old, tended to experience increasing social and behavioral difficulties in adolescence and also had an higher risk of psychological disorders such as depression.

"The term ‘autism’ likely describes several conditions," explained Dr Varun Warrier, senior author of the research. "For the first time, we have found that early and late identified autism have different biological and growth-related characteristics."

No Two Categories, But a Spectrum

The experts do not advocating for a move towards two diagnostic categories, explaining that such a step could be unhelpful for the numerous that are in between.

"It represents a gradient," Warrier commented. "Additionally, there are many other elements that contribute to when someone is diagnosed, so the moment you move from averages to anything that is relevant to an individual, it's misleading to compare."

Rising Autism Spectrum Diagnoses

These findings emerge when autism identification has risen steeply, with a almost 800% increase in cases in the UK between 1998 and 2018.

Experts say this is due largely to a broadening of the diagnostic criteria and increased awareness of the disorder.

Variability and Categories in Autism

And, while autism is characterized by having challenges with interacting with others, sensory processing, and restrictive actions, there is significant variability in how these difficulties present between individuals.

Researchers have been investigating whether the population forms subgroups, with shared traits or paths, that could make researching autism more tractable.

Research Methodology and Biological Findings

This latest research analyzed behavioral information from several study groups and genetic data from two large investigations, with over 45,000 individuals.

In the past, it was generally assumed that those identified sooner tended to be those with more marked autistic traits, underpinned by people carrying a higher proportion of autism-linked gene variants.

Yet, the recent study uncovered a different trend.

Distinct Biological Patterns and Developmental Trajectories

This analysis found that the biological genetic patterns differed between those diagnosed with autism sooner and later in life, with only a small overlap.

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

• Those identified before the age of six years tended to be delayed to walk and have trouble interpreting hand gestures and often show communication and social challenges that appeared soon but remained consistent.
• Those identified after the age of 10 years were more likely to develop an increase in challenges during adolescence and, by late adolescence, presented with more severe difficulties.

"It makes me hopeful that additional subgroups will come to light, and each will receive an suitable identification," commented an expert in cognitive development, who was independent in the study. "Now is the moment to realize that ‘autism’ has turned into a mixed collection of different disorders."