Autism has long been perceived as a condition that is predominantly seen in males. This probably comes from its initial description: Leo Kanner reported seeing eight boys and three girls with it in 1943, and Hans Asperger’s four initial case reports in 1944 were all of boys. Research since then has been biased toward understanding males with the condition, and there is an urgent need to understand more about females.
For example, in a report published 8 August in Brain, my colleagues and I showed that among high-functioning adults with autism, males and females show substantial differences in the characteristics of their brain structures1.
However, what the initial ‘male bias’ in prevalence reflects is something quite complex.
First, it may mean that the definition of autism commonly used nowadays, which is based on behaviors, is by design better at identifying males with the condition2, 3. If females with autism, despite having the same core cognitive-behavioral characteristics as males with the condition, present differently in their behavioral repertoire, the current diagnostic criteria may miss them.
Second, it may also mean that on top of the potentially male-biased criteria, in real-world clinical settings practitioners are also biased toward diagnosing males more readily than females4. Girls tend to receive their clinical diagnoses later5, for example, and compared with boys who have similar levels of autism traits, girls are less likely to be diagnosed unless they have other behavioral or intellectual issues6, 7.
Finally, in the long process of growing up and interacting with peers, and in the larger social context, females tend to learn to mask or camouflage their difficulties8, 9. This, on the other hand, may also be due to better compensatory strategies developed through years of rehearsal.
So what do these all add up to? We should critically reflect on what defines autism and revisit the male predominance in prevalence. Even if there is indeed a gender bias in prevalence, this should not mean that research should also be biased toward males. In neuroimaging studies, for example, male participants outnumber females 8 to 1 in studies of brain volume10 and 15 to 1 in cognitive task-evoked functional magnetic resonance imaging studies11.
What we understand about autism to date might be fairly male-biased. Especially when it comes to research, we are probably quite agnostic about the similarities and differences in how autism presents in different sexes/genders.
There have been increasing efforts over the years to understand the similarities and differences between males and females with autism. One heuristic, but perhaps not entirely accurate, thought is that similarities imply shared underlying processes resulting in the emergence of autism, and differences imply sex/gender-distinct factors that substantially contribute to heterogeneity in the spectrum.
Behaviorally, girls with autism seem to have less repetitive and stereotyped behaviors than boys12. Biologically, early brain growth trajectories13-16, genetic profiles17, 18 and serum biomarkers19 might all be different in some aspects between males and females.
In our new study, my colleagues and I scanned the brains of 60 adults with autism, half of them males and half females, along with the same number of controls. To confirm some analyses, we also analyzed data from a larger male sample from the U.K. Medical Research Council’s Autism Imaging Multicentre Study consortium (84 males with autism and 84 male controls).
We compared the volume of distinct brain structures in the participants with and without autism. If autism manifests in the same way in males and females, the patterns in males and females would be quite alike. If it manifests differently by sex/gender, on the other hand, the two patterns would be quite distinct.
We found it to be the latter — that is, we found minimal similarity between the patterns in men and women. The data suggest that autism manifests differently in males and females in terms of brain volume changes.
We also found that in ter