Autism is traditionally thought of as a condition associated with early childhood¹. Yet a growing number of affected individuals are now being identified later in life, including during late childhood and beyond^2–4. This shift may partly reflect changes in how autism and its associated traits are understood, particularly in cases where early signs are subtle or less apparent during the first years of development⁵. Later identification is also frequently accompanied by comorbid mental health conditions, underscoring the need to better clarify the contributors that influence diagnostic timing^6,7.

Earlier work has linked several social, demographic and clinical factors to age at autism diagnosis⁸, but these explain only a small fraction of the variability in diagnostic timing. This gap prompted a team of SFARI-funded researchers at the University of Cambridge, including SFARI Investigator Simon Baron-Cohen and led by Varun Warrier, to examine whether genetic and developmental profiles differ depending on age at diagnosis. Although autism is highly heritable⁹, the contribution of genetic risk to diagnostic timing has remained poorly defined.

The team analyzed longitudinal data from four independent cohorts of autistic individuals, focusing on polygenic influences — the aggregate effects of thousands of common genetic variants, called single-nucleotide polymorphisms or SNPs, that collectively shape complex traits. Using genome-wide association studies, the researchers examined the relationship between these polygenic profiles and diagnostic age. This approach revealed two broad socioemotional and behavioral developmental trajectories associated with age at diagnosis, rather than a single, uniform pattern.

Individuals diagnosed earlier in life showed more pronounced differences in social and communication abilities during early childhood. In contrast, those identified later were more likely to experience behavioral and social difficulties that emerged or intensified during adolescence, along with an increased likelihood of comorbid attention-deficit/hyperactivity disorder and mental health conditions, including depression and post-traumatic stress disorder.

Together, these findings challenge the idea that autism represents a single condition driven by a uniform set of genetic risk factors. Instead, the results support a developmental framework in which distinct constellations of polygenic influences are linked to different diagnostic timelines. The authors further note that females are, on average, identified with autism at later ages than males, emphasizing the importance of accounting for age at diagnosis when examining sex differences in autism. In this context, some reported sex differences may be partly attributable to differences in diagnostic timing rather than biological sex alone. For example, the higher prevalence of mental health conditions observed in autistic female individuals compared to autistic male individuals diminishes when analyses are restricted to individuals diagnosed before age five⁷. Careful consideration of age at diagnosis may therefore be essential for accurately interpreting findings related to autism, sex differences and concurrent conditions. Understanding how autism-related features emerge and change across development, from early childhood through adulthood, may improve both diagnosis and support for autistic individuals.

1. Kanner, L. Nervous Child. 2, 217–250 (1943)
2. Schendel D.E. and Thorsteinsson E. JAMA. 320, 1811–1813 (2018) PubMed
3. Russell G. et al. J. Child Psychol. Psychiatry. 63, 674–682 (2022) PubMed
4. Jensen C.M. et al. J. Autism Dev. Disord. 44, 1808–1818 (2014) PubMed
5. Lord C. et al. Nat. Rev. Dis. Primers. 6, 5 (2020) PubMed
6. Jadav N. and Bal V.H. Autism Res. 15, 2112–2125 (2022) PubMed
7. Rødgaard E.M. et al. Acta Psychiatr. Scand. 144, 475–486 (2021) PubMed
8. Daniels A.M. and Mandell D.S. Autism. 18, 583–597 (2014) PubMed
9. Havdahl A. et al. Psychol. Med. 51, 2260–2273 (2021) PubMed