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Study questions large head size in autism

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Virginia Hughes
20 June 2013

Heady bias: Studies that rely on dataset norms are more likely to report large heads in children with autism than are those that locally recruit controls.

Two new studies raise questions about one of the most frequently reported biological signatures of autism: a larger-than-normal head.

Leo Kanner's original description of autism noted this so-called macrocephaly, and dozens of studies have since reported that children with autism show accelerated head growth in their first two years of life.

Most of this work relied on biased control samples, according to an analysis of 34 studies, published 23 May in Biological Psychiatry1.

Only 7 of the 34 studies are “methodologically robust,” meaning that they followed the same children over time and relied on controls recruited from the same geographic region as the participants with autism. Four of the seven studies found significantly faster head growth in those with autism compared with controls, but three did not.

“It was a bit of a shock to me,” says lead investigator Armin Raznahan, a staff scientist at the National Institute of Mental Health’s Child Psychiatry Branch. “Like everyone else, I’ve written papers that include the sentence: ‘Early brain overgrowth is one of the best replicated findings in autism.’” 

Another study, published 10 June in the same journal, also throws some cold water on the link between macrocephaly and autism2.

That study looked at head circumference in 7,225 individuals enrolled in the Simons Simplex Collection, a genetic repository of autism families. (The collection is sponsored by the Simons Foundation, SFARI.org’s parent organization.)

After accounting for sex, height, weight and genetic ancestry, the researchers found that children with autism do tend to have larger heads than their unaffected siblings, but the difference is small: just 2 millimeters on average. What's more, just 89 of the 1,889 children with autism have a head circumference that is at least two standard deviations from the average, but only 53 of those are bigger than average; the other 36 are smaller.

New normal:

Still, researchers who have been working in this field say there’s compelling evidence that children with autism have larger brains, if not larger heads, than controls do.

“We’re all only doing head circumference as an indirect measure of brain,” says Joe Piven, professor of psychiatry at the University of North Carolina, Chapel Hill, who was not involved in the new work. For the past few years, Piven’s team has been scanning the brains of the younger siblings of children with autism at 6, 12 and 24 months of age.

Piven’s results have not yet been published. But preliminary data “clearly shows” brain enlargement between 12 and 24 months in children who develop autism, he says. “So I’m pretty sure it’s a real thing,” Piven says. “Whether head circumference picks it up routinely or not, I don’t know.”

The size of an infant’s head depends on many factors, genetic and environmental, so head-growth patterns can vary among countries or even cities.

To save time and money, many research teams rely on head circumference norms, such as the dataset published by the U.S. Centers for Disease Control and Prevention (CDC), rather than recruiting controls from the same community as the participants with autism.

“People use them because it’s easy — you just look them up on a table,” Piven says.

For years, though, researchers have raised doubts about the validity of standardized growth charts.

For example, in 2010 Carrie Daymont and her colleagues analyzed head-size data from 75,000 children in a primary care network from birth to 2 years old. Beginning at 6 months old, this group of typically developing children showed significantly larger heads compared with norms described by the CDC and the World Health Organization (WHO)3.

The CDC norms are based on a small sample — 3,803 head measurements of boys and 3,629 of girls, notes Daymont, assistant professor of pediatrics and child health at the University of Manitoba in Canada.

“That is not a large sample if you are trying to accurately estimate extreme percentiles such as the 95th or 97th,” she says. “I believe that we are very likely to be identifying an excess number of children as having unusually large heads.”

Raznahan says he was struck by Daymont’s paper because some of the studies reporting macrocephaly in autism used the CDC data as controls.

In his new analysis, Raznahan found that 11 of the 34 studies in his analysis used CDC norms and 18 tapped into similar datasets, such as those from the WHO and the 47-year-old Tanner growth curves from the U.K.

Raznahan’s analysis found that studies using locally recruited controls are significantly less likely to report enlarged heads than are studies that use population norms.

He also looked at head size data from the medical records of 35 boys with autism. At no time between 2 and 18 months was their head growth significantly different from a comparison group of locally recruited controls, he says. And at about 6 months or older, children in both groups showed markedly larger heads compared with the CDC and WHO norms.

Still, some studies using local controls do find large heads in children with autism. "I believe the authors go too far in calling into question the reports of enlarged brain growth," says David Amaral, research director of the MIND Institute at the University of California, Davis.

His team has found, for example, that some boys with regressive autism have abnormally large heads. The new Simons Simplex Collection study also found that regression is associated with macrocephaly, as are certain genetic mutations.

"We concluded that the phenomenon of early brain overgrowth was certainly real," Amaral says, "but only applied to a subset of children with autism spectrum disorder."

News and Opinion articles on SFARI.org are editorially independent of the Simons Foundation.


1. Raznahan A. et al. Biol. Psychiatry Epub ahead of print (2013) PubMed

2. Chaste P. et al. Biol. Psychiatry Epub ahead of print (2013) Abstract

3. Daymont C. et al. Pediatrics 126, e836-842 (2010) PubMed


Name: ASDDad
21 June 2013 - 10:33AM

It is now quite obvious that there are different aspects to a child poorly framed as "Autistic". Differing pathways suggest that there will be different physiological features as well as differences in genetics and thus neurological outcome.

The acknowledgement must be made that environment and genetics are and never have been stand alone 'features they are interlaced just as much as is the biology of the mother and her womb.

Should I mention the microbiome ?

Name: Aspie Doctor
25 June 2013 - 2:53PM

There is so much variation in genotype, why would any reasonable person think they could draw reasonable conclusions about phenotypes by simply averaging across a whole random sample? These "metastudies" are frustratingly uninformative and simply muddy the water.

Name: Amanda
25 June 2013 - 2:59PM

I wish we could just move on from head size. It has been 15 years of quibbling over head circumference. It is very clear if you spend time with babies and toddlers that children who regress and then develop autism have very large heads. This is due to brain inflammation. I wish all the many millions spent studying and restudying and restudying head circumference could be directed to more deserving gap areas in research.

Name: Sam
25 June 2013 - 8:49PM

well said.

Name: Bushy Van Eck
26 June 2013 - 10:46AM

The following explanation is certainly not meant to be mathematically correct but rather a means of explaining the concept thereof very briefly.

Two millimeters in diameter would represent the brain size of a fly where twenty centimeters in diameter would represent the brain size of a human. One “moment in time” at the level of the fly would be perceived as lasting ten times as long as that at the human level. This would mean that if a fly could, he would read a book ten times over for every one time a human can read that same book. A human would see a fly acting ten times as fast as himself where a fly would see our every movement to be lasting ten times as long hence our every movements to be extremely slow.

As such the smaller the brain the faster the specie would conceptualize time experiencing much more time during any one moment but yet with much less clarity and intensity. On the other hand the larger the brain becomes the slower the perception of perceived time but with much more clarity and intensity.

This now brings us to why brains are meant to develop at different rates among the different species.

A child needs to learn far more complicated lessons than an animal and as such the development of his brain, but more importantly the increase in brain size needs to occur over a much longer duration to allow for lessons to be learned.

What we have learned about the fly and the human is very important to enable us to grasp the significance of brain size.

A babies brain at birth is say half the size compared to that of an adults brain. We can now safely assume that the babies mind would encapsulate time to be lasting twice as long as that of his parent and as such would perceive each and every movement, every single sound and all the rest to be lasting twice as long hence everything being very slow in the mind of the baby.

This is a very clever trick of evolution to allow more time in the mind of the baby, enabling it to take note of and learn the lessons to be learned in a slow but meaningful way. Imagine someone showing you a complicated task without slowing it down, you would be totally lost, not being able to have followed all the moves, if any at all. It would be like trying to follow the flight path of a fly. When we teach someone a new trick we will only manage to do so if we slow our actions down, enabling that person to follow the procedures.

This is a safety mechanism build into all species literally allowing for more time and as such enabling them to follow all actions with ease getting to learn the lessons to be learned. As the child grows older he would slowly develop a different sense of reality, but in direct relation to the increase of his brain, which by the way is also why a child would see a holiday lasting for ages compared to his parents. It would be pointless to constrain the minds of animals from maturing faster since their lessons to be learned are far less complex.The growth rate of any specie is directly linked to its level of intelligence but yet brain size in relation to intelligence is insignificant.

Name: Bushy van Eck
26 June 2013 - 10:59AM

As a note of importance; I have discovered the realities relating to our existance and the functioning of the mind many years ago after 25 years of self analysis and studies including everything else relating to the human mind. This include for example the true realities of Sleep Paralysis, Deja Vu, what the subconscious really entails, literally everyhing. Problem is that despite having a IQ higher than most university professors without having even finishing high-school and also having so called Spectral disabilities no one will give me a chance.
I write this with the best of intentions having the wellbeing of humanity first and foremost in my mind.

Name: Bushy Van Eck
26 June 2013 - 1:44PM

It is extremely important to keep such children away from any fast paced actions especially cartoons playing of too fast which would only amplify the problems. Parents should also endure to speak at a slower pace as well as learn to teach the kids everyday tasks at a slower pace especially during the early stages. This will allow them to follow through on the importance of the lessons to be learned as no one can learn at a pace faster than his comprehension abilities directly related to his perceived realities of time.
Need I really say more?

Name: Ivea
11 October 2013 - 6:19AM

I don't understand your comment about speaking slowly or comprehension. My daughter has autism and is a genius. She learns more quickly than I do and retains much more. She speaks and writes slowly, with a lot of pauses. However, she can repeat what she's heard on tv back to me verbatim, weeks later. The thing she learns fastest is infomercials. Then, when she sees a product in the store that she's seen on tv she starts repeating all the selling points.

Name: Bushy Van Eck
22 October 2013 - 6:33PM

My comment was published 26 June.
Look at the following video Published on Oct 15, 2013 which actually substantiates what I wrote about teaching kids at a slower pace etc.
Link added below.
In this beautiful duo from a father and daughter, we hear about how a family fought autism and came winning. A strong message of hope and fighting invisibility.

In the spirit of ideas worth spreading, TEDx is a program of local, self-organized events that bring people together to share a TED-like experience. At a TEDx event, TEDTalks video and live speakers combine to spark deep discussion and connection in a small group. These local, self-organized events are branded TEDx, where x = independently organized TED event. The TED Conference provides general guidance for the TEDx program, but individual TEDx events are self-organized.* (*Subject to certain rules and regulations)
Here is the link


Name: lvea
11 October 2013 - 6:09AM

My daughter has Asperger's. At her three month checkup the doctor showed me the chart of head circumferences and said that her measurement was off the chart large. Her height and weight were high but were within the range of the charts. He then apologized that he hadn't done a c-section when she was born because her head was so big at birth and it caused me damage. We had discussed during the long labor that we (parents) have large heads and can never find hats to fit us. I have one parent with large head and some asperger traits. I had gestational diabetes (which could cause bigger baby).

Name: Cathy B.
11 March 2015 - 12:55AM

When I was born I was kind to my mother. I exited a breach rather than big head first. My butt was smaller then.

Name: Shannon
27 December 2013 - 6:19AM

Iodine levels, thyroid issues, inflammation....all genetic and dietary issues that can be controlled. Head size, all her first year (from four months on), my daughter's head measured above 95% and twice was above 100%. Her ped was asked about Autism, as there is a high occurrence of it in my family. She assured me that my daughter met milestones and had no symptoms. Now, less than one year later she's severely Autistic. Brilliant, but most communication is repetitive at best.

Name: sam
23 May 2014 - 4:43PM

Stumbled across this... My daughter has recently had an aspergers diagnosis. Her head size seems normal, only slightly large I suppose. I have been wondering if there is something genetic because I have a much larger head than what is deemed normal. My head circumference is 24" and I am a woman. I haven't had a diagnosis but I think I do have aspergers...

Name: lisa embery
7 March 2015 - 6:58PM

My son is Autistic, his head was large when he was born 45cm. Nothing was said to me.?? At 7 after fighting for our diagnosis. He was diagnosed.

Name: Cathy B.
11 March 2015 - 12:51AM

I just went to a doctor appointment and the doctor asked me if I was ever Autistic because she noticed my large head. I said I had been diagnosed as Autistic as a child. I came home and googled this and came to your site. Now I know why I wear a man sized ski hat and always wore uniform covers of a larger size when I was in the Navy and the Army. I've been asked by the VA if I have had Autism but denied it because I fear losing my benefits. The doctor I saw just now was not VA. I mostly kept my condition a secret in the military too and my recruiter told me that Autism qualified as a DADT condition. I was high enough functioning that I could serve my country and got out due to an in service leg injury that got worse over time. So Autism creates bigger heads, now I wonder if that ancient Egyptian Pharoah, Akhunaton who is portrayed with a huge head may have suffered from Autism. An interesting concept to say the least.

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