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A Surplus of Males

This is a guest blog post from Autism Speaks Science Board member John Elder Robison, author of Look Me in the Eye: My Life with Asperger’s and Be Different: Adventures of a Free-Range Aspergian.

I spent this Tuesday in Washington, reviewing autism research proposals.  I really enjoy that work, because it puts me among some of the best minds in autism science.   In the course of our discussions, an intriguing question arose.

We know autism is far more common in males, but the reason why remains elusive.  It’s one of those facts of autism that most people take for granted, and simply accept for what it is.  In earlier essays on this blog I have considered possible explanations, from Simon Baron Cohen’s theory that autism is “exaggerated maleness” to reasons why females might be undiagnosed and undetected.

All the explanations I have heard so far do not account for this interesting observation:

If the male/female ratio within a society is 50/50, any random group of families sould have a 50/50 distribution of sons and daughters. Some families would have one child, others would have three.  Some would have all sons and others two daughters and a son.  Taken together, we would expect the total of sons and daughters to be equal.

If we assemble a collection of families in which there is at least one autistic child, that distribution of sons and daughters is not 50/50.  It favors the males.  Any autism researcher who has worked with families knows that to be true, even in the absence of hard studies to quantify it.  Why?

All of us know families that have all sons or all daughters.  We don’t make anything more of that that we do tossing a coin and having it come up heads three times in a row.  Just chance, we say.  But when you identify a group of families with a trait like autism, and they all have more sons than daughters . . . suddenly it stops looking random and starts to seem the result of something else.

If this were a roll of the dice, you’d start to think the dice were loaded.

One explanation is that some parents have a son with autism and stop having children.  So the girls that might even the male/female ratio are never born.  I think that explanation may be true today, but what about the ages before modern birth control?

Critics might say that we don’t know how autism was distributed among the sexes a hundred years ago, and that’s true.  The autism diagnosis has only existed for sixty-some years.  Yet we do have strong anecdotal evidence.  Using that, some modern day people have “diagnosed” historical figures with autism based on what we know of them and their lives.  How many of those individuals are female? Almost none.

Those “post-mortem diagnoses” are certainly subject to challenge and I’m sure some are even wrong.  That said, they can’t all be wrong and the male-female ratio in the known historical record of autism remains strikingly tilted toward the male side.

Geri Dawson suggested another possible explanation for the male-female imbalance.  What if girl embryos are actually more susceptible to some factor implicated in autism, but in a different way?  The factor that produces autistic baby boys might result in unsuccessful pregnancies when the fetus is female.  The result – fewer baby girls with autism are born.

To the best of my knowledge, no one has studied pregnancies in families with autism.  All that has been studied are the resultant children.  We don’t know how many miscarriages may have preceded or followed the birth of an autistic boy.  The incidence of miscarriage in general has been studied and it would be interesting to know if families with autism deviate from the norms in that regard.

The son-daughter imbalance certainly ties in with the Baron-Cohen “maleness” theory.  If autism indeed an expression of excessively male genetic material, that imbalance might result in more males being born in those families.

I spoke to several scientists and it became clear that this is one of those obvious questions that has never really been answered.  There is the general belief that autism families contain more males, but we have no hard data to illustrate the difference.  We also don’t have any multi generational data, which could shed light on the heritability of the condition.

In my own family, I have one child, a son with Asperger’s.  My father had many Aspergian traits, but he died before anyone thought to explore that possibility.  He had a brother, and no sisters.   His father also had a brother and no sisters.  His grandfather had three brothers and a sister.  Is there a pattern there that relates to autism?  I really don’t know.

It would be very interesting to see a study that addressed this question.  Perhaps a grad student somewhere will read this, and bring a research proposal to our next review meeting . . . .

Stranger things have happened.

  1. LLP
    September 28, 2011 at 12:08 pm

    My family would blow this theory completely out of the water; I have only two sisters {who remain childless} and no brothers, my father an only child – paternal grandmother had one brother, paternal grandfather only child, my mother had one brother – maternal grandmother had one sister, maternal grandfather one brother

    my husband only child, through his father’s {two brothers one sister} second marriage one half brother and half sister {both currently childless}
    his mother no clue she’s adopted

    My son an only child and not because of the autism – he is 8 and we’ve only known for 2 years

  2. grainofsalg
    September 28, 2011 at 12:20 pm

    What about the theory that something hormonal during pregnancy interacts with boys differently than girls? I have also read theories relating to the use of pitocin during childbirth, pitocin, of course, being an artificial hormone . . .

  3. Wendy
    September 28, 2011 at 12:20 pm

    The theory about just having boys and no girls and that is why these couples produce autisic children is not connect. because my husband has a sister and he has traits of autism and she does not and he has two boys and one has autism and the other does not and his sister has four boys and one has autism.

  4. Tara
    September 28, 2011 at 12:22 pm

    I have four children all of which have the same father. Three girls one boy. All of my girls have autism and my boy does not. So this is not the case for my family.

  5. Sue Rodgers
    September 28, 2011 at 12:24 pm

    This is worth someone looking into. I have a son diagnosed with ASD. I had another son (NT), then I had a miscarriage and then a daughter. The last two were with a different father though. I believe my son’s father is AS. He has two brothers and twin sisters (Identical so counts as one really). I believe one of those brothers has AS. On my side of the genetics, I do not see much autism. My mother says she has some traits, like high IQ, likes to read, bad at directions (that’s her symptoms for diagnosis). She’s too socially appropriate, organized and a good multi-tasker. So, she’s not AS. What about all those women in history that were not written about because women were “less than”. Maybe some of those women had autism traits. I almost wish I were back in grad school to research this topic. I hope someone does.

  6. Kim M.
    September 28, 2011 at 12:28 pm

    I’m a parent to 5 children, two boys and three girls. The boys have Aspergers and high-functioning autism, respectively and my oldest daughter has selective mutism but is being followed. My youngest daughters appear to be typical.

    As it so happens, my husband and I just discussed this last night. Our sons were diagnosed after our daughters were born. Would we have had our girls if we had been aware of the autism sooner? It’s a possibility I do not want to consider. I do recognize that my family is not typical for the times. Most people do not elect to have a family as large as ours. This may be contributing to the slanted number of boys, or possibly not. Research here would be very interesting.

  7. September 28, 2011 at 12:28 pm

    I have three children with autism….2 of the three are girls.

  8. September 28, 2011 at 12:35 pm

    just anecdotal. I have a brother, who is now 40, who has aspergers. My 9 yr old daughter – my fist born, has Asperger’s. She was also a micro-preemie born at 26 wks who almost did not survive. I had 3 subsequent documented ( and one or 2 suspected very early ) miscarriages. Then a second child, born full term – an NT girl.

    BTW – I know of at least 3 other girls on the spectrum who all were also micro-preemies. I have long wondered if there was something in their brains that “told” them to come so early, or if perhaps something in the preemie experience was the environmental “trigger” necessary to assert the latent autistic tendancies…

    this is interesting food for thought!!! Thank you for raising it in scientific circles!!!!!

  9. September 28, 2011 at 12:35 pm

    Interesting. We don’t use birth control. We have 4 daughters (including a set of identical twins) and one son. Our middle daughter has autism. Our son, the oldest, has some autistic traits but not enough to make me want to go through the evaluation process whereas my daughter, while high functioning, is undeniably autistic as well as having ADHD and epilepsy. There are autistic traits all throughout my mom’s side of the family, she has only sisters.

  10. Kirby
    September 28, 2011 at 12:56 pm

    A very good read – thank you! I am especially intrigued by the possibility of an in-utero risk factor causing more female miscarriages. I hope this does inspire some revealing research.

  11. September 28, 2011 at 12:58 pm

    I’m curious about why it’s predominately a boy diagnosis as well. My son, age 9, was diagnosed with Aspergers last year after being diagnosed with ADHD for years. My daughter, age 6, does not seem to follow the Aspergers traits, but does have more anxiety than normal and she does often make many of the movements my son does that I associate with the Aspergers. Otherwise, she’s a very typical child.

    This leads to me to wonder if the girls from autism families that aren’t diagnosed with a form of autism have any other behaviors that aren’t completely typical, but not intrusive enough to be an autism. Hmmm..

  12. September 28, 2011 at 1:12 pm

    I have a family much like LLP’s: all males on my father’s side for progeny, and on my mother’s side, scarce males (and one of those is mentally retarded. He’s my favorite uncle.) There are six males on my father’s side (my other uncles) and my mother fondly remembers growing up with 22 female cousins (and two brothers.) My parents produced me (female) and two brothers: so far, the three of us have produced what could possibly have been 14 offspring (six surviving.) We know three of the eight were female, and four of the six survivors are female. Adia, my eldest daughter, is the Aspie here: her siblings are twin girls three years younger. None of the other children have a spectrum disorder diagnosis. No other children on my mother’s or father’s side have a spectrum diagnosis. We’re just the interesting house here.

    I read an article that suggests a connection between each of close pregnancies and Down’s syndrome: Adia was born precisely a year after her stillborn elder sister with Down’s syndrome. It’s worth explaining those links, I think, to see where female autism comes from.

  13. September 28, 2011 at 1:19 pm

    Interesting. If there is a skewing towards a general male imbalance in families with autism, then an easy thing to check might be sperm motility in the fathers. Are the sperm carrying the x chromosome more or less robust than the one carrying the Y chromosome in fathers of male leaning families? Another possibility – Is there something in the uterine environment that favors maleness?

  14. Katie Wright
    September 28, 2011 at 1:34 pm

    Hi John, The ratio is 4:1, or probably greater than that now, because testosterone binds to heavy metals and various toxins. Conversely, estrogen acts as a protective function, protecting a girl – to a greater degree at least- from heavy metal exposures.

    It has now been established that autism (by AGRE and others) is at least 50% environmental in cause. Our male children are much more vulnerable to pollution, Hg in fish, mercury emissions from coal burning power plants and yes, in my son’s case the toxic preservatives in vaccines. Poor methlylators, most so whom are male, cannot excrete these toxic substances efficiently.

    • September 28, 2011 at 5:24 pm

      Hi Katie Wright,

      Is there anyway you could post links to the medical studies that you got your information from? I am extremely interested and would love to read them. Thanks for posting!

  15. Amanda Bates
    September 28, 2011 at 1:47 pm

    I have had six pregnancies. First a miscarriage at 9 weeks, second, a 12 year old girl with Asperger’s traits and Mixed Bipolar Syndrome and Sensory Processing Disorder, third, a 10 year old boy with pronounced Asperger’s Syndrome and Sensory Processing Disorder, fourth a miscarriage at 8 weeks, fifth, a perfectly “normal” 7 year old girl, and sixth, a miscarriage at 13 weeks. At that point we decided to have my tubes tied. My husband, his brother, and one of his 3 sisters all have Asperger’s traits to some degree. Two of his sisters had multiple miscarriages and eventually gave birth to a “normal” son and “normal” girl and boy, respectively. The other sister had three girls. One of my sisters has four girls while the other has a “normal” girl and a severly ADHD boy. Interesting thought behind this article. I would be curious to find any correlation.

  16. September 28, 2011 at 2:07 pm

    My son was diagnosed on the low end of the spectrum, highly functional.. When he was sent to have his Gene’s tested, they found an extra “piece” on chromosome 15.. they tested me and I have that as well, however I’ve never had any developmental issues (mother).. Father has not been tested yet, but does anyone know where I can somehow see if there are more cases that are similar???

  17. caseysqed
    September 28, 2011 at 2:21 pm

    Most autistic males seem to have significant speech delays or speech problems. Males are typically less verbal than females by their nature, so females might be more prone to overcome the speech problems thus hiding the autistic symptoms or at least masking them to seem to be a different disorder. The lack of speech seems to be the first trait noticed in boys, thus getting them recognized and better diagnosed than their female counterparts.

  18. September 28, 2011 at 3:35 pm

    Very interesting. I have a boy and a girl – my son has autism, my daughter is in the gifted program. My husband was one of two boys – his brother was never diagnosed, but has most the traits of high functioning autism. My husband’s dad was one of two boys and he’s the same as my brother in law – undiagnosed autism or aspergers for sure.

  19. Tracey Young
    September 28, 2011 at 4:02 pm

    my husband is the youngest of four boys. His father was an only child.His mother , the oldest of four (two and two).
    My husband fathered four children – all boys – two in one marriage and two in our marriage. The older boys are fine, the younger two – one has Aspberger’s one has Autism.

    My father was the youngest boy in a family , three boys one girl. I am the oldest of three, two girls, one boy. Both my sister and I have son’s with Autism.

    if as you say there is the maleness theory of Autism, I can believe it.

  20. September 28, 2011 at 5:41 pm

    The historical data would be inconclusive, at best, because there are far more male historical figures than female ones. Without knowing the cause of autism, it’s really impossible to say why there is such a disparity in the autism rates between the sexes. The genetic causes (that are known) only account for a small fraction of cases.

    There are several examples of diseases and conditions not striking in a statistically fair way. Certain types of muscular dystrophy rarely affect females. There needs to be more research into the causes of autism.

    On a personal level, I have a son and daughter, neither of which is NT, with no family history on either side (plenty quirky, but no diagnosis or suspicions of autism).

  21. Katie Wright
    September 28, 2011 at 6:25 pm

    Hi Michelle,
    great study discussing on ASD/ males and testosterone
    regarding greater vulnerability of boys to environmental toxins
    check them out at PubMed

  22. Sarah
    September 28, 2011 at 10:17 pm

    An article related to this…

    Testosterone may bump autism rates in males
    The disorder is four times more commen in males than females, MSNBC report by By Karen Rowan


  23. Gene Bensinger
    September 29, 2011 at 10:03 am

    Thank you, John. This idea is excellent evidence why the IACC is a critical component in helping construct a roadmap for research and why AS (and a diverse representation from our community) needs to have seats at the table. There is a ton we don’t know and this information is, as you say, pretty darn basic. Good ideas come from everywhere, not just the scientists and academics.

    Regarding one of your thoughts, it is a very, very recent development that diagosis happens regularly before age 4 or 5 (Autism Speaks effort have had a lot to do with that progress!) So I don’t think that many parents, especially young ones in prime childbearing years, would have been able to make a decision to cease having any more kids based on ASD. Their first child with ASD would have been very unlikely to have received a diagnosis before a second pregnancy occurred. A ton of siblings are born with 2 years spacing.

  24. September 29, 2011 at 11:56 am

    Has anyone ever checked into the use of prenatal vitamins during pregnancy? It just seems that we are better cared for as far as good nutrition and taking vitamin supplements during pregnancy and more and more children are being diagnosed on the Autisim spectrum?

  25. Lisa
    September 30, 2011 at 5:45 pm

    Well, I have 4 children…my 2 oldest girls are ages 21 and 16…my 21 yr old is a Senior at UK and after she graduates….she is going on to complete her Master’s degree as a Speech Patholigist (my youngest son, age 6…was diagnosed at age 2 with moderate to severe autism) he was her inspiration….she always excelled in school…was in advance classes…made Straight A’s…President of her class her Sophmore, Junior and Senior yr of High School. Now, my other daughter age 16 is following in her sister’s footprints…she actually maybe even a little more intelligent….the only difference is…my oldest daughter has always been a leader and take charge kind of person…my youngest daughter is not necessarily a follower…more like a leader within small groups…she is a Junior in High School and is still undecided on where her future might take her….Now, getting to my boys, my oldest is 14 and very socially awkward….had speech problems most of his early childhood and recieved speech therapy…it was recommended that I hold him back another yr in preschool…which is what I did..I feared he would have learning problems or may have ADD (I have ADHD) but, every year his teachers always said he doesn’t have a problem concentrating…he makes mostly A’s and B’s with an occassional C…..but, it worries me because he doesn’t have any close friends….doesn’t respect people’s “boundaries”….he will sit too close to someone when its obviously making that person uncomfortable, and sometimes I feel like he doesn’t quite “grasp” what I’m telling hiim….he could ask me where the mayo is in the fridge and it will be literally exactly where I tell him and its like he doesn’t understand when I say “second shelf” I actually mean look on the second shelf…yet, his teachers say the opposite…now, getting to my youngest son…he is 6 yrs old now…finally starting talking at age 4….if I had to guess, I would say he is more high functioning…he is starting to read on a third grade level and is doing math on a third grade level….his hand writing is just as neat as an “typical” child….and if your not around him long enough…most people don’t know he has autism…but, he gets constant “praise” and one on one attention (I have him in a private school for children with learning differences) So, my point being…I don’t know why but, I believe there is some reason why boys are more susceptible than girls…but, if you ask most nurses…the majority of them will tell you premature girls have a higher survival rate….now, why is that? It may be one of those mysteries that will never be explained…..but, I think finding the cure and the cause is the most important thing to focus on anyway….

  26. Bharbara Gudmundson
    September 30, 2011 at 8:27 pm

    I have been doing work on an environmental issue that for 70 years has been affecting every living thing on the North American Continent. In 1991 I began working on the issue of the release of garbage leachate on to streets and lanes in North American cities and towns. In 1938 compactor garbage trucks began to be used in North American cities while at the same time during the 1930’s, 1940’s and 1950’s there was a large increase in the types of chemicals being created and thrown into the garbage. These compactor trucks contain many combinations of chemicals that are the results of what kinds of garbage is picked up in various districts. We line our landfills with geomembrane linings (that are as thick as 60 garbage bags laid out one on top of the other) in an attempt to contain the garbage leachate that is created because of the dangers presented to the area the landfill is built on. Before the trucks ever get to the landfill a great deal of the garbage leachate in the garbage has been released while the truck driver travels his/her route. These are compactor trucks and during the compacting the solids are separated from the fluid similar to what happens when you squeeze an orange to separate the juice.
    My environmental work has been the investigation of the release of garbage leachate on to streets and lanes of North American communities. For twenty years my work has been to photograph and film the release of garbage leachate and inform all levels of government and organizations of what is occurring. When I hear, during the investigation and discussions about the causes of Autism and that there is an environmental factor it always leads me to believe there is a co-relation with my environmental work. This question keeps coming to the forefront whenever I hear about the environmental factors being put forward where Autism is concerned. Many times I have attempted to ensure the researchers in Autism organizations understand there may be a co-relation.

    Research from October 2008 to April 2009

  27. Lora Brown
    October 1, 2011 at 4:45 pm

    Very interesting ideas. I have one son that is on the mild end of the spectrum. I have two sons and one daughter. My other son shows some spectrum traits as well. My husband and his family also show many traits as well. I feel that some complications at birth may have added to the degree of my son’s symptoms. Have you ever looked into this aspect? If a family has a genetic predisposition, does the birth process affect the outcomes? Even if this does not account for every case of autism does it maybe explain some of the increase in the number of cases seen today?

  1. September 28, 2011 at 4:38 pm

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