Corpus Callosum Volumes in Children with Autism Spectrum Disorders: Sex-Associated Differences.

Zhang et al. (2023) scanned the brains of toddlers aged two to four. Half had autism. Half were typically developing.

They measured the corpus callosum, the big cable that links the two sides of the brain. They looked at boys and girls separately.

Kids with autism had larger corpus callosum volumes. The difference was biggest in girls.

The finding flips an older rule of thumb that says the callosum is smaller in autism.

Boger-Megiddo et al. (2006) saw a smaller callosum in preschoolers once they corrected for overall brain size. Yun did not correct, so both can be true: raw volume up, proportion down.

Cox et al. (2015) found no size difference in a huge mixed-age sample. Toddlers may be the only window where the enlargement shows up.

Li et al. (2024) adds that, in older youth, girls with autism also show unique network wiring. The sex-specific story holds past the toddler years.

If you assess little kids, know that bigger callosum volume can mark autism, especially in girls. Do not expect the same clue in school-age clients. Add sex to your checklist when you review neuroimaging or decide on early targets.