Persistence of megalencephaly in a subgroup of young boys with autism spectrum disorder.
Lauren E Libero, Christine W Nordahl, Deana D Li and 3 others
PMID 27273931WHAT IT FOUND
In boys with autism, a subgroup with brain size disproportionate to height kept enlarged brains through about 5 years.
Their head growth became larger than controls by around 24 months, while height did not differ.
Key findings
01At Time 1, 19 boys with autism were classified as having brain size disproportionate to height.
02The subgroup with disproportionate megalencephaly had significantly greater total cerebral volume than the other autism boys and typically developing boys at each MRI time point.
03Head circumference became significantly larger in the disproportionate megalencephaly group by around 24 months, although it did not differ from the other groups at birth.
STILL TO COME
How it was doneWhat they foundWhat it means for OTs
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What it does not show
The study included only boys, so it does not describe girls with autism. It followed children only from about 3 to 5 years. It cannot say what happens in later childhood, adolescence, or adulthood. The subgroup definition used a cutoff of 1.5 standard deviations above the control mean. The paper notes that any cutoff on a continuous measure is somewhat arbitrary. Not every child returned for every scan: 129 autism and 49 controls at Time 1, 84 autism and 39 controls at Time 2, and 65 autism and 31 controls at Time 3. The MRI system was upgraded during the study. Phantom calibration and distortion correction were used to reduce the effect. Head circumference was used as a proxy for brain size. The paper notes it is less correlated with brain size in older children. The authors state they do not know the neurobiological basis for the enlarged brains.
The easy way to misread this
Do not read this as evidence that all boys with autism have enlarged brains or that head size should guide therapy. The persistent enlargement was seen in a subgroup defined by MRI volume relative to height, and the study did not test whether this finding predicts function or treatment response.