Evidence against the "normalization" prediction of the early brain overgrowth hypothesis of autism.
Lisa D Yankowitz, John D Herrington, Benjamin E Yerys and 3 others
PMID 32552879WHAT IT FOUND
In autism, total brain volume stayed larger than controls across childhood, adolescence and early adulthood, and did not shrink toward typical size with age.
Larger brain size did not track symptom severity.
Key findings
01Autistic participants had larger total brain, gray matter and white matter volumes than controls, and this difference did not vary with age.
02Within the autistic group, total brain volume was not related to ASD symptom severity.
03The positive relationship between IQ and total brain volume seen in controls was absent in the autistic group.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The sample started at age 6, so it cannot show whether brain volume normalized before age 6. The study compared different people at different ages, not the same people followed over time, so age differences cannot be read as individual brain growth trajectories. The autistic and control groups were not matched for IQ, sex, or race. The autistic group had lower mean IQ, and race differences required sensitivity analyses. The replication sample was all male, had 175 participants, and did not reproduce the IQ-by-diagnosis interaction, so the primary IQ finding may not generalize to girls. The study reports brain biomarker differences, not therapy outcomes, so it does not tell therapists what treatment to provide.
Declared interests
The work was supported by the National Institute of Mental Health, the National Institute of Child Health and Human Development, the National Science Foundation, the Pennsylvania Department of Health, the Robert Wood Johnson Foundation, Pfizer, and Shire Pharmaceuticals. The supplied text does not state author conflict-of-interest declarations.
The easy way to misread this
Do not read larger brain volume as evidence of more severe autism. In the autism group, total brain volume was not related to any of the three symptom severity measures.