News The latest developments in autism research.

Genetics: Head size heterogeneous in autism

by  /  6 March 2013

Big bones: A subset of people with autism who have large heads are also much taller and heavier than average.

Children who have autism and large heads may belong to different clinical subsets based on the ratio between their head size and height, according to a study published in the February issue of Autism Research1.

The results suggest that these subgroups could point the way to distinct genetic risk factors.

About 20 percent of people with autism have macrocephaly, defined as a head circumference that is above the 90th percentile (or above the 85th percentile for people who are shorter than average). A small study using postmortem brains suggests that this may be the result of excess neurons in the brain.

Children with autism who have large heads may also weigh more and be taller than controls. This suggests that macrocephaly is one aspect of an overall increase in their body size.

In the new study, researchers looked at 185 individuals with autism who were evaluated at the medical genetics clinic at the University of California, Los Angeles, between 2008 and 2011. Of these, 33 have macrocephaly. The researchers compared their height, head circumference and weight with standard averages from the 2010 Centers for Disease Control and Prevention growth charts

Of the 33 people with macrocephaly, 5 have a mutation in PTEN, an autism risk factor linked to large head size. All but one of these individuals have extreme macrocephaly, with a head size in the 99.7th percentile or above, the study found.

Of the remaining 28 individuals, 10 have a head circumference that is more abnormal than their height (disproportionate macrocephaly) and 12 have a head circumference and height that are both larger than average (relative macrocephaly). The researchers also categorized six participants with macrocephaly who are especially tall and heavy (above the 95th percentile for each).

Each of these subsets is accompanied by its own set of distinguishing symptoms, the study found. For example, of the ten people with disproportionate macrocephaly, eight have low muscle tone and five have a flat nose. About half of the people with relative macrocephaly have a bent pinkie finger, but only two have low muscle tone and one has a flat nose.


1: Klein S. et al. Autism Res. 6, 51-56 (2013) PubMed

2 responses to “Genetics: Head size heterogeneous in autism”

  1. Christine says:

    I have 2 children on the spectrum. Both have large heads and even though they were both premature they were very long and are both tall for their age. My son has poor muscle tones and my daughter has a flat nose and both my pinkie fingers are bent. I used to be a handful when I was a child but was never diagnosed with anything.

  2. Amy L says:

    I am a mother of 5 children. My 5 year old has speech difficulties and is in speech therapy. He is improving slightly but to begin with he replaced constanents in the beginning of words like the M in milk he would replace with an F….saying Filk. He did this even though he was able to say the M sound. I would TELL him , “MA -MA- MA- MOM” and HE COULD REPEAT IT. BUT I WOULD SAY, “MA-MA-MA-MILK” AND HE WOULD SAY BACK, “MA-MA-MA- FILK”. ODD, RIGHT? I have often thought he was acting oddly compared to other children. I will hear him say something incorrectly …like,”Her wants her toy back.” and I will correct him as I always have for all my kids, but its as if he doesn’t get it. I never hear him say it correctly from my demonstration. Its as if nobody ever corrects him. I am certain thats what his teachers must be thinking. I hear him sing songs from school like ,”mary had a little lamb…her dont know where to find it.” Obviously he has heard the song repeatedly at school but the words arent sinking in… Does this sound like some autism spectrum disorder symptoms?
    He didnt so much as blink when I left him at his first day at preschool & then kindergarten. Even though he is rarely left anywhere. He had problems at first in preschool. He got in trouble for hitting other children several times. Had to go to school disciplinary meeting over it once. Kindergarten he seems to be doing better behavior-wise.
    He has always had a large head circumferrance (95% at last report). He also is in the obese weight range, yet specifically doctor told he that he IS NOT OBESE..just very muscular. I often hear him repeating very annoying sounds. Its as if he is comforted by these noises…for example the high pitch noises you would expect dolphins to make. Repeating them until I think I may go insane at times and have to ask him to stop.
    He has always had problems playing with other children. He just doesn’t get along well. He will hunt down silky tags on shirts or blankets and continually rub these. He used to spin himself on one knee wildly in a circle. until you would think it would make him sick. I am right aren’t I? Don’t these sound like autistic behaviors to you guys? anybody with any helful info please e-mail me at :

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