Sex differences in brain structure: a twin study on restricted and repetitive behaviors in twin pairs with and without autism.
Annelies Van't Westeinde, Élodie Cauvet, Roberto Toro and 4 others
PMID 31893022WHAT IT FOUND
In twins, higher repetitive behavior scores linked to thicker brain tissue in the right intraparietal sulcus in females only.
Males showed no such structural link in the main analysis. This suggests different biological pathways for these symptoms in girls and boys.
Key findings
01Within twin pairs, higher restricted and repetitive behavior scores were associated with increased cortical thickness in the right intraparietal sulcus in females, but not in males.
02When controlling for other autism symptoms, females showed additional associations with increased thickness in the right postcentral sulcus and increased volume in the right orbital and postcentral gyri.
03In males, no significant associations between brain anatomy and restricted and repetitive behaviors were found in the main analysis, though some emerged when controlling for social interaction deficits.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
The sample size was relatively small (75 pairs), and the study was exploratory. The mean severity of repetitive behaviors was low in the sample, which may have limited the ability to detect strong associations. Females with autism in the sample were older than males with autism, which could confound the results since brain structure changes with age. The study relied on a specific statistical threshold (FDR corrected q < 0.05) and some findings were only significant at a more lenient threshold (q < 0.1). It is a cross-sectional study, so it cannot determine if the brain differences cause the behaviors or result from them.
Declared interests
The authors declared no competing interests. The study was supported by multiple Swedish funding bodies including Vetenskapsrådet, VINNOVA, and Hjärnfonden.
The easy way to misread this
Do not interpret the lack of significant findings in males as evidence that repetitive behaviors have no biological basis in boys. The study was underpowered for sex-specific comparisons, and the authors note that males showed associations when controlling for social deficits, suggesting the pathways may be more complex or obscured by other factors in this sample.