“[T]he age at which a person is first diagnosed with autism varies considerably… These differences in developmental timing have conventionally been attributed to differences in severity… Zhang et al. present evidence that the developmental timing of autism diagnosis is not simply an artefact of the challenges of identifying milder cases at early ages, but rather a primary feature that distinguishes distinct forms of autism.”
“Zhang et al. first examined longitudinal data describing socioemotional and behavioural development in three cohorts of autistic individuals. In each cohort, the authors identified two subgroups. These exhibited qualitatively distinct trajectories of development that corresponded with age at diagnosis. A ‘unitary’ model of autism assumes that the developmental timing of diagnosis is a function of severity… Rather, in all three cohorts, difficulty levels in early childhood were similar across the subgroups and increased throughout development only for the later-diagnosed subgroup. By late adolescence, this subgroup presented with more-severe difficulties. This observation is consistent with a ‘developmental’ model that treats timing of diagnosis as a qualitative feature of the condition, as opposed to simply a result of severity.”
“Zhang et al. found that early-diagnosed autism and late-diagnosed autism had distinct polygenic profiles. In other words, specific [genetic] variants associated with risk, and their effects on risk, differed by subgroup.”
“Zhang et al. found that the genetic effects on timing of autism diagnosis persisted at full strength after adjusting for a range of developmental milestones. They also found that distinct genetic factors representing early and late diagnosis contributed independently to autism-case status, even after accounting for genetic factors that underlie a range of psychiatric disorders. The authors further established that their results were not driven by sex differences in genetic profiles of autism risk — a key concern given that girls are often diagnosed with autism later than are boys.”
This is a summary of a recent large-scale analysis by Zhang et al. I find this work rather interesting… as it definitely challenges my assumption that diagnosis timing is just a matter of severity. Also worth mentioning that the late-diagnosed group scored significantly worse on several mental health metrics.
The paper itself (open access): https://www.nature.com/articles/s41586-025-09542-6
Is it genetic, or an outcome of having zero support system as a result of basically being ignored and treated like we’re just “weird” or “not trying hard enough,” with no explanation for why we are the way we are?
I’m willing to bet if I was given proper accommodations and not treated like a deficient burden by my family and school I’d be much more emotionally resilient and well.
Seriously, there’s plenty of studies correlating early trauma to worse mental and physical health outcomes over a person’s lifetime. This is validating in a way, but to imply it’s fated and innate feels shortsighted.
In a similar vein, my first thought was “did they control for economic factors?” Lower-income families are less likely to have adequate healthcare, less likely to enroll a child in pre-school or daycare, less likely to see an educator intervene if the child is missing milestones.
Especially in the US, there’s a history of conflating economic factors for genetic factors because of who has historically held wealth. Turns out playing golf doesn’t make you live longer, it’s just that if you can afford to play golf, you can probably afford healthcare and more nutritious foods.
This is an excellent question… they mentioned it in the intro section that “… previous studies have shown that individual clinical and sociodemographic factors explain only a small proportion (typically less than 15%) of the variance in age at autism diagnosis”. They also addressed it a bit deep in the supplementary materials. Copied below:
- Demographic factors: Parental characteristics
We ran a few analyses to understand if parental characteristics can impact age at autism diagnosis, primarily through gene-environment correlations.
- Longitudinal analyses: In the longitudinal analyses of birth cohorts, accounting for ethnic minority status, parental socio-economic status, material deprivation, and maternal age at birth does not impact the variance explained by the GMM latent trajectories on age at autism diagnosis.
- Genetic analyses: In SPARK, controlling for parental socio-economic status and neighbourhood deprivation does not significantly attenuate the SNP heritability for age at autism diagnosis.
So I think the answer is yes, they did control for economic factors, and the effect is minimal
I’m almost certainly convinced that good early childhood intervention helps a lot. The paper also pointed out that the late-diagnosed geoup scored significantly worse on depression, self-harm, and other metrics… Even though the late diagnosed ones probably tend to have less severe symptoms (like how my diagnosis is supposedly “low support needs”). Not sure if early intervention was the sole cause of the massive discrepancy in mental health status here but it very much could be
I think the paper is more focused on genetics simply because of the field though. It is well known that ASD has a strong genetic component so there’s no denying that. But ASD is currently linked to like 300+ genes… I would presume that genetic discrepancy is what made some researchers interested in that. There was an accepted paper earlier this year by Olga Troyanskaya’s group that was also trying to see if there are different " subtypes" of Autism so to speak (https://doi.org/10.1038/s41588-025-02224-z)
Also I’m hoping that works like this can lead to better early detection and intervention (and hopefully not the other way)
“Best we can do is Tylenol”
— United States Department of Health and Human Services
