Different genes, different paths: What controls the timing of autism?

Autism does not follow the same path for everyone. Some children show traits early, while others go unnoticed until adolescence.

A new study from the University of Cambridge uncovers why this difference exists. The work shows that genes, not just environment, influence when autism becomes visible.

The team wanted to know if timing followed one genetic pattern or several. To test this, they looked at genetic data and developmental records from large international cohorts. The result reshapes how scientists view the spectrum.

“We found that, on average, individuals diagnosed with autism earlier and later in life follow different developmental pathways, and surprisingly have different underlying genetic profiles,” said Xinhe Zhang, lead author of the study.

Two autism paths

The researchers compared two ideas. The first, called the unitary model, assumes one shared genetic path.

In that view, early and late diagnoses differ only in intensity. Those diagnosed later carry fewer autism-related variants, but the biological foundation is the same.

The second, the developmental model, tells another story. It argues that separate genetic routes lead to autism at different ages. The underlying idea is that biology shapes not just how strongly traits appear but when they do.

The study put both ideas to the test using data from thousands of children.

Following different autism paths

The researchers followed children through multiple stages of growth. They used behavioral scores that track emotional and social changes from early childhood to the teenage years.

Children diagnosed early often showed visible differences right from the start – stronger communication challenges, more intense behavioral traits, and quicker divergence from peers.

On the other hand, children diagnosed later appeared typical at first. Gradually, differences surfaced as they aged.

The contrast between these two paths was striking. It suggested that some children’s brains follow a faster developmental rhythm, while others change more slowly before traits stand out.

Genes affect autism timing

Genes played a clear role in this timing. The researchers calculated how much of the variation in diagnosis age could be explained by genetics. They found that common genetic variants accounted for a meaningful share of the difference.

That finding shifts the conversation. Timing is not only about parental awareness or medical access. It is partly written in DNA. Some genetic patterns make traits visible early, while others delay them.

This discovery strengthens the developmental model. It shows that autism’s timeline carries a heritable component, much like height or temperament.

Early and late autism forms

The analysis uncovered two clusters of genetic influence. One group of variants linked to early-diagnosed autism also appeared in conditions involving stronger developmental impact. These variants often related to brain growth and early learning differences.

The other group connected to later-diagnosed autism. These variants showed weaker links to developmental delay but stronger ties to traits like higher educational achievement and subtle social differences.

In short, early-diagnosed autism reflected heavier neurodevelopmental load, while later-diagnosed forms reflected quieter influences that emerged gradually. Both belong to the spectrum, yet they arise through partly separate genetic routes.

Beyond family and society

Social and demographic factors did not explain much. Sex, socioeconomic status, and maternal age together accounted for only a small slice of the variation in diagnosis age. More importantly, these influences did not change the genetic patterns observed.

That means timing differences cannot be reduced to environment alone. Access to services and cultural norms may decide when recognition happens, but they don’t create the underlying developmental rhythm.

The study points to an inner mechanism – genes interacting with brain development – to decide how soon traits become visible.

Timing is heritable

One of the study’s most striking ideas is that genetics can set the tempo of developmental expression.

Two children might carry similar overall risk for autism, yet one shows traits in preschool, while another appears typical until middle school.

This timing difference is not random. It reflects how inherited variants guide brain maturation and behavior over time. Some variants accelerate divergence from typical development; others slow it down.

The idea that timing itself can be heritable broadens what scientists mean by “genetic risk.” It’s not only about who is autistic but when autism unfolds.

Genes link to autism traits

The research also showed that these genetic patterns connect differently to other traits. The variants related to early-diagnosed autism overlapped more with attention and learning difficulties. Those linked to late diagnosis overlapped more with intelligence and academic success.

This separation underlines that autism’s genetics are multi-dimensional. One pathway leans toward early developmental difference; another aligns with later, socially oriented variation.

The boundaries between these routes remain blurred, but both shape the diverse experiences seen within the spectrum.

What “the spectrum” means

The findings challenge the old belief that autism differs only by severity. Instead, it may differ by developmental route. Two children can reach the same diagnosis through distinct biological processes.

That insight matters for practice. Early-emerging autism may require different support strategies than later-emerging forms.

Clinicians could use this understanding to tailor interventions, predicting which children need help sooner and which might benefit from different developmental monitoring.

The research also helps explain why one diagnostic label covers such a wide range of experiences. The spectrum may be better understood as overlapping pathways, not a single line running from mild to severe.

“The term ‘autism’ likely describes multiple conditions. For the first time, we have found that earlier and later diagnosed autism have different underlying biological and developmental profiles,” explained Dr. Varun Warrier, an expert in Cambridge’s Department of Psychiatry.

“An important next step will be to understand the complex interaction between genetics and social factors that lead to poorer mental health outcomes among later-diagnosed autistic individuals.”

Autism as a moving target

This study paints autism as a process, not a fixed condition. Genetic variation doesn’t just decide whether someone is autistic. It shapes when and how autism becomes visible.

The work implies that biological timing is as important as behavioral traits themselves. Recognizing this can lead to more flexible support systems, especially for people whose differences appear later and may go unnoticed for years.

The message is clear: autism’s diversity runs deeper than outward traits. It lives in the rhythm of development, influenced by genes that set the pace long before diagnosis.

Broader view of human variation

By linking genetics, behavior, and timing, this study reframes autism as part of natural human diversity. It does not treat late diagnosis as lesser or delayed recognition as failure. Instead, the research shows that multiple developmental rhythms coexist within the spectrum.

Understanding those rhythms can lead to fairer, more precise diagnosis and support. It may also encourage society to view autism not as static difference but as an evolving expression of human biology.

“Our findings suggest that the timing of autism diagnosis reflects more than just differences in access to healthcare or awareness, important as these are,” said Zhang.

“However, it is important to note that these are average differences on a gradient, so earlier and later diagnosed autism are not valid diagnostic terms.”

The study is published in the journal Nature.

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