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Macrocephaly: Unwrapping Autism and Head Size

September 28, 2023

Have you ever heard of macrocephaly? This big word has a very simple definition: it means that a person has a large head.

Macrocephaly: Unwrapping Autism and Head Size

But is this condition a problem for children, and does it have any connection to autism spectrum disorder (ASD)? Let’s take a look at these questions and more.

What is macrocephaly?

Macrocephaly is typically defined as when someone’s head circumference is larger than the 98th percentile for their age group. The condition usually becomes evident within the first year of life, as that’s when a child’s brain grows the fastest. Brain growth slows down afterward, and most children have gained 90% of their adult head size by the age of three.

Sometimes, larger head size is just a trait passed down by families. In this case, it’s known as “benign familial macrocephaly” and is accompanied by a larger brain size. A small portion of kids with this type also have a learning disability or developmental delay.

Other times, a large head is a symptom of something more serious, such as excess fluid, brain tumors, chronic hematomas, intracranial bleeding, or an infection.

There are also two types of macrocephaly: disproportionate and proportionate. “Proportionate” means that the large head still looks appropriately sized to a large body. A child with disproportionate macrocephaly will have a head size that appears mismatched to the rest of their body.

Is macrocephaly associated with autism?

A high head circumference has been noted in some children with autism ever since the condition was first identified. Leo Kanner studied several children with repetitive behaviors, social withdrawal, language delays, and attachment to routines. His 1943 paper, Autistic Disturbances of Affective Contact, introduced awareness of “Kanner’s syndrome”, later known as autism.

Kanner noticed that some of the subjects had large heads, though he didn’t expound much on it. Since then, researchers have looked more into the prevalence of head overgrowth in autistic kids.

Sacco et al. (2015) looked at over 200 pieces of research on head size and brain size in individuals with autism. The report concluded that autistic patients had significantly larger head circumferences than the general population, with 15.7% having actual macrocephaly and 9.1% having brain overgrowth. Other research estimates that as high as 35% of individuals with autism have an “abnormally” large head size.

Brain imaging has found that macrocephaly in children with autism is typically due to larger brain volume, not excess fluid or non-brain tissue. One report, Courchesne et al. (2001), found that 90% of their participants with autism had larger-than-average brain volumes in early toddlerhood.

Why is there a macrocephaly-autism connection?


There aren’t conclusive answers to this, but one study, Klein et al. (2013), points to a specific gene mutation. In this clinical study, the researchers examined 33 autistic patients with macrocephaly between the ages of two and 18. The participants’ head sizes were above at least the 90th percentile for their age group.

Five of the children with autism were found to have mutations in their PTEN gene. This gene is responsible for making an enzyme that regulates cell division and suppresses the growth of tumors. All but one of those five had extreme macrocephaly, meaning their head size was above the 99.7th percentile.

However, the children who had disproportionate macrocephaly didn’t display this mutation. The researchers don’t know why these differences exist, but there could be a separate genetic source behind their large heads and/or their autism.

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General overgrowth

A 2011 study by Chawarska et al. observed that overgrowth of the whole body may be a sign of autism…at least in boys, since boys were the only participants of the study. The researchers looked at 184 boys; 98 had a diagnosis of autism or PDD-NOS, and 31 had global developmental delay or other mental difficulties like attention deficits. A total of 55 were typically developing children.

The children with autism had a similar head circumference as the neurotypical children at birth. However, by the age of 9.5 months, their heads were significantly larger. Meanwhile, the boys with other delays didn’t have significantly bigger heads than the neurotypical kids.

Autistic participants started showing significant growth in height compared to the typically developing ones around the age of five months. Significant differences in weight occurred around 11 months. Overall, only the children with autism showed overgrowth in all three categories: head size, height, and weight.

Furthermore, the researchers’ analysis revealed that the autistic boys with the most extreme overgrowth also showed more intense autism symptoms at age two. Although not all kids with autism will present with overgrowth, this evidence suggests that such accelerated growth may accompany a more severe form of autism.

Does brain overgrowth cause autism?

Courchesne et al. (2003), suggested that there are four distinct stages in the brain development of people with autism. According to this article, the brains of babies with autism are actually a bit smaller than average at birth. Then, there is rapid brain overgrowth within the first year of life during the second stage. This growth slows in the third stage, so that brain size is almost at its maximum around age four or five. This maximum size is actually close to the maximum size of neurotypical brains—but children with autism reach it about eight years earlier than normal. The fourth phase is a gradual decline in brain volume from childhood to adulthood, until the autistic brain isn’t much bigger than the neurotypical brain.

This study suggests that this early period of brain growth may cause, or at least contribute to, autism. According to Courchesne: “the developing human brain is designed to benefit from an extended period of experience-guided growth.” This period allows most children to grasp the cognitive, social, and linguistic skills that many kids with autism struggle with.

The researchers speculate that this period is compressed into a shorter amount of time in autistic brains, causing the infant to become overwhelmed, withdraw from the world, and miss out on the early building of these functions.

Psychiatry still doesn’t have definite answers for the “why” behind autism, but accelerated brain growth could indeed play a role.

Is macrocephaly a problem?

Generally, no. A larger head shouldn’t cause issues for your child with autism later on.

However, macrocephaly can be caused by factors other than autism or family traits. Keep an eye out for the following symptoms to make sure your child’s large head isn’t due to something more serious:

  • Unexplained vomiting
  • Strange eye movements
  • Tightness or bulging on head
  • Irritability
  • High-pitched crying

These could indicate harmful excess fluid, extra growth of the skull bones, or other problems.

In conclusion

The medical world has been interested in the relationship between head size and autism for decades now. Although not all people with ASD will have noticeably large heads, it’s a common trait among people on the spectrum. Some researchers believe that fast brain growth, even if it doesn’t rise to the level of macrocephaly, may explain symptoms of autism.

It’s always best to talk to your doctor if you have concerns. But in general, macrocephaly isn’t something you need to worry about.


Brennan, D. (2021, April 22). What You Should Know About Macrocephaly. WebMD. https://www.webmd.com/brain/what-you-should-know-about-macrocephaly

Chawarska, K., Campbell, D., & Chen, L. (2011, October). Early Generalized Overgrowth in Boys With Autism. Archives of General Psychiatry, 68(10), 1021-1031. https://jamanetwork.com/journals/jamapsychiatry/fullarticle/1107307

Cohmer, S. (2014, May 23). “Autistic Disturbances of Affective Contact(1943), by Leo Kanner. The Embryo Project Encyclopedia. https://embryo.asu.edu/pages/autistic-disturbances-affective-contact-1943-leo-kanner

Courchesne, E., Karns, C. M., Davis, H. R., Ziccardi, R., Carper, R. A., Tigue, Z. D., Chisum, H. J., Moses, P., Pierce, K., Lord, C., Lincoln, A. J., Pizzo, S., Schriebman, L., Haas, R. H., Akshoomoff, N. A., & Courchesne, R. Y. (2001, July). Unusual brain growth patterns in early life in patients with autistic disorder. Neurology, 57(2), 245-255. https://n.neurology.org/content/57/2/245

Klein, S., Sharifi-Hannauer, P., & Martinez-Agosto, J. A. (2013, February). Macrocephaly as a Clinical Indicator of Genetic Subtypes in Autism. Autism Research, 6(1), 51-56. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3581311/

MedlinePlus. (n.d.). PTEN gene. MedlinePlus. https://medlineplus.gov/genetics/gene/pten/#conditions

Sacco, R., Gabriele, S., & Persico, A. M. (2015, November). Head circumference and brain size in autism spectrum disorder: A systematic review and meta-analysis. Psychiatry Research: Neuroimaging, 234(2), 239-251. https://www.sciencedirect.com/science/article/abs/pii/S0925492715300573?via%3Dihub

Williams, C. A. (2008, August). Macrocephaly sydromes [R.C.P.U. NEWSLETTER]. University of Florida Division of Genetics and Metabolism. https://genetics.pediatrics.med.ufl.edu/wordpress/files/2020/01/macrocephaly.pdf

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