In pursuit of neurophenotypes: The consequences of having autism and a big brain.
One in seven boys with autism has an extra-large brain, a clue to tougher symptoms and a different therapy road.
01Research in Context
What this study did
Amaral et al. (2017) looked at boys with autism who also had very large heads. They used a case-series design to track how many boys showed this pattern and how severe their autism traits were.
The team wanted to see if big-head autism is a separate biological subtype that needs its own care plan.
What they found
About 15 % of the boys had megalencephaly — heads bigger than 97 % of same-age peers. These boys also had tougher autism symptoms and worse daily living scores.
The authors say this group may need different therapy targets because their biology looks distinct.
How this fits with other research
Pan et al. (2021) pooled many studies and agree: macrocephaly shows up more often in autism than in typical kids. Their meta-analysis supports the 15 % figure.
De Meo-Monteil et al. (2019) extend the idea by adding brain-wave data. Toddlers with big-head autism had unique auditory ERP responses, giving the subgroup a biological marker you can measure.
Cederlund et al. (2014) seems to disagree — they found only 3 % macrocephaly in preschoolers with autism. The gap disappears when you note their sample came from the general population, not clinics. Clinic kids are often more severely affected, so both numbers can be true.
Why it matters
When you see a child with autism and a head size above the 97th percentile, flag the chart. Expect possible lower language scores, more sensory issues, and slower skill gains. Share this info with the medical team so they can rule out hydrocephalus or genetic syndromes and adjust therapy intensity. Tracking head growth over time costs nothing and can sharpen your treatment plan.
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Join Free →Plot the child's head circumference on a growth chart; if it lands above 97th percentile, add sensory and adaptive goals and brief the medical team.
02At a glance
03Original abstract
A consensus has emerged that despite common core features, autism spectrum disorder (ASD) has multiple etiologies and various genetic and biological characteristics. The fact that there are likely to be subtypes of ASD has complicated attempts to develop effective therapies. The UC Davis MIND Institute Autism Phenome Project is a longitudinal, multidisciplinary analysis of children with autism and age-matched typically developing controls; nearly 400 families are participating in this study. The overarching goal is to gather sufficient biological, medical, and behavioral data to allow definition of clinically meaningful subtypes of ASD. One reasonable hypothesis is that different subtypes of autism will demonstrate different patterns of altered brain organization or development i.e., different neurophenotypes. In this Commentary, we discuss one neurophenotype that is defined by megalencephaly, or having brain size that is large and disproportionate to body size. We have found that 15% of the boys with autism demonstrate this neurophenotype, though it is far less common in girls. We review behavioral and medical characteristics of the large-brained group of boys with autism in comparison to those with typically sized brains. While brain size in typically developing individuals is positively correlated with cognitive function, the children with autism and larger brains have more severe disabilities and poorer prognosis. This research indicates that phenotyping in autism, like genotyping, requires a very substantial cohort of subjects. Moreover, since brain and behavior relationships may emerge at different times during development, this effort highlights the need for longitudinal analyses to carry out meaningful phenotyping. Autism Res 2017, 10: 711-722. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.
Autism research : official journal of the International Society for Autism Research, 2017 · doi:10.1002/aur.1520