Gyrification patterns in monozygotic twin pairs varying in discordance for autism.

Researchers looked at brain scans from identical twin pairs. One twin had autism, the other did not. They measured how folded the outer brain surface was in each twin.

The team compared these twins to a control group of identical twins where neither had autism. This design let them hold genes constant while seeing brain differences linked to the disorder.

Both the autistic twin and the unaffected co-twin showed extra folding in the right parietal area. Controls with no autism diagnosis did not show this bump.

In typical kids, more brain folding tracks with higher IQ. In both twins - sick or well - that link was broken. Folding no longer predicted smarts.

Lanfranchi et al. (2021) seems to disagree. In a general population sample, kids with more autistic traits had less folding, not more. The clash likely comes from who was scanned: diagnosed twins versus community kids with mild traits.

Froehlich et al. (2013) used the same twin trick but looked at head size instead of folding. They also found the trait in both twins, backing the idea that some brain signs are inherited even when only one child meets autism criteria.

Joosten et al. (2009), published the same year, warned that classic twin concordance numbers may miss early environmental hits. The folding data now give a concrete picture of such an environmental echo.

If you assess a child with autism, remember that subtle brain differences may also show up in the "unaffected" identical twin. Use the same developmental watch list for both siblings. When you see unusual parietal folding on an MRI report, do not assume it equals autism - check IQ and adaptive skills separately, because the normal folding-to-intelligence link can be missing.