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Based on experts who studied genetic information from more than 45,000 autistic individuals across Europe and the US, the condition must not be regarded as a single condition with a common root cause.

The international research revealed that individuals diagnosed with autism early in childhood, typically before age six, tend to have a different genetic profile than those identified later.

Key Findings from the Study

• Early-diagnosed children tended to exhibit behavioral challenges from a young age, including difficulties in social interaction, but remain consistent over time.
• Individuals identified with autism at an older age, typically past ten years old, tended to experience increasing social and behavioral difficulties in adolescence and also showed an higher likelihood of psychological disorders like anxiety.

"The term ‘autism’ probably refers to multiple conditions," explained the lead researcher, senior author of the research. "Initially, we have found that earlier and later diagnosed autism possess distinct underlying and developmental profiles."

No Two Categories, Rather a Spectrum

The scientists do not advocating for a shift towards dual diagnostic groups, explaining that such a step might be counterproductive for the numerous who are in between.

"It represents a gradient," Warrier commented. "There are also many other elements that contribute to age of diagnosis, so the moment you move from general trends to anything that is applicable to an individual, it's misleading to compare."

Rising Autism Identification Rates

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

Specialists explain this is due largely to a widening of the assessment guidelines and greater awareness of the disorder.

Diversity and Subgroups in Autism

Furthermore, while autism is characterized by experiencing challenges with interacting with others, responding to senses, and repetitive behaviors, there is huge variability in how these difficulties present between people.

Researchers have been investigating whether the group clusters into categories, with common characteristics or paths, that could make researching autism more manageable.

Study Methodology and Genetic Insights

The latest research used behavioral information from four birth cohorts and biological data from multiple extensive investigations, with more than 45,000 participants.

In the past, it was generally assumed that those identified sooner were usually those with more marked autistic features, underpinned by people carrying a greater proportion of autism-linked gene variants.

However, the recent research uncovered a distinct trend.

Distinct Genetic Profiles and Behavioral Trajectories

The analysis found that the biological genetic profiles differed between those diagnosed with autism sooner and later in life, with only a modest overlap.

Their typical genetic profile of older-diagnosed autism is more similar to that of ADHD, as well as to mental health disorders such as anxiety and PTSD, than it is to autism diagnosed in young children.

• Individuals diagnosed before the age of six years were more likely to be delayed to walk and have difficulty interpreting hand gestures and tended to experience social and communication challenges that appeared soon but stayed stable.
• Individuals identified after the age of 10 years were more likely to experience an rise in difficulties during adolescence and, by older teenage years, displayed more severe difficulties.

"It makes me hopeful that additional categories will be identified, and every one will find an appropriate diagnostic label," commented an expert in cognitive development, who was independent in the study. "It is time to understand that ‘autism’ has turned into a ragbag of various conditions."