Head circumference as an early predictor of autism symptoms in younger siblings of children with autism spectrum disorder.
In high-risk baby siblings, a rapid-then-slowing head growth pattern between 12 and 24 months hints at later autism symptoms.
01Research in Context
What this study did
The team followed 170 baby brothers and sisters of kids already diagnosed with autism.
They measured head size at 12 months and again at 24 months.
Then they watched who later showed autism symptoms and who did not.
What they found
Babies with bigger heads at 12 months were more likely to develop autism traits.
The red flag was a head that grew fast, then slowed down between 12 and 24 months.
This odd deceleration pattern was the strongest signal.
How this fits with other research
Balaum et al. (2026) later confirmed the link in a huge community sample.
They saw 6- to 9-fold higher autism odds for heads in the top or bottom 5 percent.
Cederlund et al. (2014) seemed to disagree: only 3 percent of preschoolers with autism had large heads, matching typical kids.
The gap is timing: the 2008 and 2026 papers looked at babies, while Mats looked at 3- to young learners.
Head size may normalize by preschool, so infant measures matter most.
Stewart et al. (2018) found no link when they scanned babies inside the womb.
Again, the window matters: prenatal head growth differs from the 12- to 24-month window studied here.
Why it matters
If you serve families who already have one child with autism, pull out the tape measure.
Plot head size at the 12-month and 24-month visits.
A fast-then-slow curve is a cheap, quick cue to start early screening and refer for intervention sooner.
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02At a glance
03Original abstract
Siblings of children with autism have an increased risk for autism spectrum disorders (ASD). As children with autism often exhibit an atypical trajectory of head circumference (HC) growth, HC may be an indicator of vulnerability to autism. This study investigated whether infant siblings of children with ASD (n = 77) with an atypical trajectory of HC growth were more likely than those without an atypical HC trajectory to develop autism symptoms. Results showed that infants who had larger HC at 12 months, and whose HC growth rate decelerated more rapidly between 12 and 24 months were more likely to exhibit autism symptoms than infants with more typical HC trajectories. Among infant siblings of children with autism, atypical HC growth might alert pediatricians to provide screening and/or referral for further evaluation.
Journal of autism and developmental disorders, 2008 · doi:10.1007/s10803-007-0495-9