Intellectual disabilities moderate sex/gender differences in autism spectrum disorder: a systematic review and meta-analysis.

Emerson et al. (2023) pooled every paper they could find on sex differences in autism. They only kept studies that also said whether kids had intellectual disability (ID). Then they ran a meta-analysis to see if ID changed the boy-girl gap.

The review looked at three symptom areas: social skills, restricted and repetitive behaviors (RRBIs), and language. Each study was split into two groups: kids with ID and kids without ID.

ID flips the sex pattern. Girls without ID have milder RRBIs and better language than boys without ID. Girls with ID show more social, RRBI, and motor problems than boys with ID.

In plain words: once ID enters the picture, girls look more severe, not less.

Wormald et al. (2019) found no sex differences on the SRS-2 in high-functioning kids. Emerson et al. (2023) explains why: those kids mostly had no ID, the very group where sex gaps shrink.

Souza et al. (2023) also saw girls with ID pile up more RRBIs and epilepsy. The new meta-analysis backs that observation with harder numbers.

Blair et al. (2020) told clinicians to watch for sex bias; Emerson et al. (2023) gives the concrete rule—always note ID status before you compare boys and girls.

If you test a girl with ASD plus ID, do not expect the "typical" female profile of milder symptoms. She may need stronger intervention in social, play, and self-care domains than a boy of the same IQ. Update your intake forms: add an ID checkbox and adjust your expectations when it is ticked.

Yes. Across large epidemiological samples, intellectual disability (ID) is diagnosed more often in males than in females. Male-to-female ratios cluster around 1.3:1 to 1.6:1 for mild ID and are somewhat lower for severe ID, so the overall picture is a modest but consistent male excess. The gap is widest at the milder end of the range.

Several explanations are proposed. X-linked genetic conditions (such as fragile X syndrome) fall disproportionately on males because males have a single X chromosome, which raises male vulnerability to a large family of X-linked intellectual disability genes. Ascertainment also plays a role: boys are referred and assessed earlier because externalizing behavior draws clinical attention, so some of the measured gap reflects who gets identified, not only who is affected.

This is the question most searchers arrive with, so it is worth stating plainly: the research supports male overrepresentation in intellectual disability. The study on this page then asks a related but different question, which is how the presence of ID changes the way autism looks in girls versus boys.

The authors pooled 79 studies of sex/gender differences in autism spectrum disorder (ASD), covering social communication, restricted and repetitive behaviors and interests (RRBIs), sensory processing, and language and motor skills. Crucially, they analyzed autistic people without ID and autistic people with ID as separate subgroups, then compared the two.

The results reversed depending on ID status. Among autistic people without ID, girls and women showed fewer RRBIs, more sensory symptoms, and stronger language than their male counterparts, which fits the common idea of a subtler female autism profile. Among autistic people with ID, the pattern flipped: girls and women showed more social difficulties, more RRBIs, poorer language, and more motor problems than males.

The takeaway for assessment is that intellectual disability moderates sex differences in autism. A clinician who expects the low-support female profile to hold across the board will misread autistic girls who also have ID, because in that group the female presentation is more impaired, not less. Sex, ID, and autism have to be considered together rather than one at a time.