Are Sex Differences in Autism Just Normal Sex Differences?

“Although not a common focus of developmental research, a substantial body of work on adults examines the possibility that ASD sex differences are a reflection of normative sex differences. These findings raise the possibility that sex differences seen in the ASD phenotype are not unique to ASD but reflect broader sex differences in the general population” (Messinger et al., 2015, p. 2).

There’s been extensive debate about the existence of sex differences in autism. Few can argue that there’s discrepancy in rates of diagnosis of autism across the sexes, but there isn’t exactly a consensus as to why that’s the case. Some have argued, as I’ve covered before, that simply by nature of being female women are protected from genetic and environmental effects that may become phenotypically apparent in males, a theory known as the Female Protective Effect. This concept isn’t unfamiliar to us, as females, especially in the case of mutations of the X chromosome, can be silent carriers of genetic defects that are otherwise deleterious or even deadly to males because females carry a “genetic backup” of a second X. This is why mothers, more than fathers, may be more likely to pass on mildly-to-moderately deleterious mutations to their offspring because they themselves are either silent carriers or only minimally affected. Many times, the effects of these mutations may only become obvious once passed on from mother to son.

Building on a related viewpoint, researchers with the Baby Siblings Research Consortium (BSRC) published data suggesting that the Female Protective Effect may actually be reflective of typically occurring sex differences and not something that is specific to autism nor necessarily reflective of pathology. Though there has been evidence to suggest that autistic females who come from simplex families are more severely affected than their male simplex counterparts, Messinger et al. (2015) write that there is:

“evidence of greater symptom severity– particularly elevated levels of repetitive and restricted behavior– among males. In both the Autism Genome Project and a recent study of 3- and 4-year-olds, males with ASD had higher levels of repetitive behavior than females” (p. 2).

The team found that in general males across all groups lagged behind in development compared to their female counterparts and expressed more autism-related traits, though this effect was progressively more extreme in high-risk nonautistic followed by high-risk autistic siblings. And as found in previous studies, males exhibited higher repetitive and restricted behaviors than females. They found that overall sex differences weren’t weakened or exaggerated in the autism group compared to other groups, suggesting that many of the sex differences measured were indeed that: just sex differences.

This resonates strongly with the idea perpetuated within the high-functioning autistic community that women with autism do indeed exist but they are more difficult to identify and therefore harder to diagnose. Like their nonautistic female counterparts, they tend to be better at hiding their inadequacies and challenges. But rewriting our concepts of autism according to sex differences is a particular challenge given that most of the foundational work done since the 1940s has been based on males. And in that case, perhaps we need to re-address what autism “is”. Since, for instance, females with autism tend to be less severely affected in the social domain than autistic males, is it really appropriate to continue to use male-derived social scales to diagnose females? Wouldn’t it be more useful to have a broader scale instead for women?


Hans Asperger with a male patient.

Some may argue that “light autism” at that point isn’t truly autism, but if these women have milder characteristics, still suffer challenges from other related traits, and are prone to having children, particularly sons, who fall within the diagnostic range, isn’t that still a form of “autism”? As a scientist who works with genomics, I don’t agree that there is a true biological cut-off for the autism spectrum and that the boundaries we’ve demarcated are instead simply arbitrary. That doesn’t mean I think it useful to call the entire human condition “autism”– there’s a pragmatism to having functional labels in the case of providing treatment, accommodations, and self-understanding, as well as limiting our scope of research to something feasibly measurable. But I, personally, do not consider the current criteria inclusive enough, though I know others would strongly disagree with me. Autism is not a single etiological entity, we know this already; it is many similar overlapping entities that form a larger spectrum. And I believe a broader use of the term could be more diagnostically and scientifically useful. If an individual with a Broader Autism Phenotype (BAP) experiences challenges in relation to the BAP, then that, in my opinion, is also autism– even if it isn’t as debilitating as those with more severe forms. Why? Because it’s a spectrum, and there will always be someone else worse or better off, by definition.

I would relish the opportunity to study those with BAP (and I hope at some point I can) in order to better understand how autism occurs across such a large range of severity and what different risk factors underlie that occurrence. And so I’m not especially interested in clinical philosophical debates about imaginary, ever-shifting diagnostic boundaries. It sort of feels like wasted breath to me since complex biological systems don’t typically work in such an on/off fashion. I’d rather spend my time simply studying the people and see what the data has to say.

6 responses to “Are Sex Differences in Autism Just Normal Sex Differences?

  1. The baby sibs consortium group is not representative of the general population of children diagnosed with an ASD. They exclude children with an IQ less than 80 and children with neurological damage. No doubt there is in some families a familial loading of the BAP. My view is that the BAP is a background genetic effect that is always reliant on other genetic influences, environmental and/or epigenetic risk factors that cumulatively increases total individual risk. BAP features are common and continuously distributed throughout the general population. In Down syndrome with ASD there is a family loading of BAP traits that is not seen in Down syndrome with no ASD. First degree relatives with a family loading of BAP traits are not diagnosed either with Down syndrome or ASD:

  2. Gillberg and Kopp have developed a new tool that better identifies the expression of ASD features in girls in contrast to boys and should be more widely used. The differences in ASD expression in girls were “avoids demands”, “very determined”, “careless with physical appearance and dress” and “interacts mostly with younger children”.

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