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

The international study showed that those diagnosed with autism at a young age, usually before age six, often have a distinct genetic profile than those identified at an older age.

Important Discoveries from the Research

• Younger-diagnosed individuals tended to exhibit social challenges from a young age, including difficulties in social interaction, but remain stable as they grow.
• Those identified with autism at an older age, typically past ten years old, tended to experience growing behavioral and social difficulties during teenage years and also showed an increased risk of psychological conditions such as anxiety.

"The term ‘autism’ likely refers to several conditions," explained Dr Varun Warrier, principal investigator of the study. "For the first time, we have discovered that early and later identified autism have different underlying and developmental characteristics."

No Dual Categories, But a Spectrum

The experts are not advocating for a move to dual diagnostic categories, saying that such a step might be unhelpful for the numerous that fall somewhere in the middle.

"It represents a spectrum," Warrier commented. "Additionally, there are numerous additional elements that influence when someone is diagnosed, so the point you move from averages to something that is applicable to an person, it's false equivalency."

Rising Autism Spectrum Identification Rates

The results come at a time when autism diagnosis has risen steeply, 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 recognition of the disorder.

Diversity and Categories in the Condition

Furthermore, while autism is defined by experiencing difficulties with interacting with others, sensory processing, and restrictive behaviors, there is huge variability in how these difficulties present between people.

Scientists have been investigating whether the group forms categories, with common characteristics or trajectories, that could make researching autism more manageable.

Research Approach and Biological Insights

The recent study analyzed observational information from several birth cohorts and biological information from multiple extensive studies, with more than 45,000 individuals.

Previously, it was commonly assumed that those diagnosed sooner tended to be those with more marked autistic features, supported by people carrying a higher proportion of autism-linked genetic differences.

Yet, the recent study uncovered a distinct pattern.

Different Genetic Patterns and Developmental Paths

This examination found that the biological genetic profiles varied between those identified with autism earlier and later in life, with only a modest similarity.

The typical biological pattern of older-diagnosed autism is more similar to that of ADHD, as well as to mental health disorders like anxiety and PTSD, than it is to autism diagnosed in early childhood.

• Those identified before the age of six years tended to be slow to walk and have trouble interpreting hand gestures and often experience communication and social difficulties that emerged soon but remained stable.
• Those diagnosed past the age of 10 years tended to experience an increase in difficulties in adolescence and, by older teenage years, presented with more severe difficulties.

"It makes me hopeful that additional subgroups will come to light, and every one will find an suitable identification," commented an expert in cognitive development, who was not involved in the research. "It is time to understand that ‘autism’ has become a ragbag of various conditions."