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Studies Help Explain Why Autism is a Male Disorder

By Heather Turgeon |

This week, a trio of articles were published in the journal Neuron on the genetics of autism.

One of the big take-aways is that there are likely to be hundreds of genes involved in creating the behaviors and symptoms that lead to an autism diagnosis — one study found 130 to 234 regions of DNA that were linked to autism, while another found 250 to 300.

That’s not a surprise (although some news headlines have made it sound like it is) — autism researchers have been aware of how genetically complex the disorder is for many years now.

The new piece that caught my eye had to do with how and why autism affects four times as many boys as it does girls. Apparently, the girls in the study had many more autism-associated genetic mutations than the boys — so why would boys be more likely to have the disorder in the end?

The average girl with an autism diagnosis had 15.5 genetic hiccups (called “copy number variants” — here’s an earlier article in my column explaining what this means) while boys on the autism spectrum had an average of two genes altered.

That means that, for whatever reason, the genetic tipping point for girls is much higher. Girls can have the same genetic alterations to genes but not have the disorder, whereas boys appear more vulnerable and will be affected by only a few changes to their genes. For a girl, it takes a “massive hit” to her brain networks to make a difference.

Why is that? Well, it’s not the first time we’ve heard that boys tend to be more vulnerable when it comes to health and development. But the researchers also wonder if sex hormones factor in, or if the X chromosome could be involved — boys only have one, so if there’s a genetic glitch on that one, it may have more impact.

Image: flickr

 

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About Heather Turgeon

heatherturgeon

Heather Turgeon

Heather Turgeon is currently writing the book The Happy Sleeper (Penguin, 2014). She's a therapist-turned-writer who authors the Science of Kids column for Babble. A northeasterner at heart, Heather lives in Los Angeles with her husband and two little ones. Read bio and latest posts → Read Heather's latest posts →

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9 thoughts on “Studies Help Explain Why Autism is a Male Disorder

  1. Slartibartfastibast says:

    The Journal of Evolutionary Psychology just published a paper that supports the hypothesis that the confirmed neanderthal admixture event(s) provided cognitive variations that were subsequently selected for, sometimes causing a locus of deleterious recombinations in the genomes of children with parents who had selected one another for those characteristics.

    An excerpt: “The autism continuum could represent a remnant of genetic introgression that took place before humans were the lone species in our genus. Perhaps some of the genes for autism evolved not in our direct ancestral line but in a solitary subspecies which later merged genetically with our line of descent through gene flow.”

    The paper is titled “Conceptualizing the Autism Spectrum in Terms of Natural Selection and Behavioral Ecology: The Solitary Forager Hypothesis”

    More info can be found on the Wikipedia discussion page for the causes of autism (including two neanderthal genes strongly implicated in autism (CADPS2 and AUTS2), as well as evidence of neanderthal art and communication (they shared FOXP2)): https://secure.wikimedia.org/wikipedia/en/wiki/Talk:Causes_of_autism#Neanderthal_Admixture_Hypothesis

  2. John Best says:

    Testosterone makes mercury more toxic so that it kills brain cells quicker. Estrogen has the opposite effect. The ratio of autistic boys to girls has nothing to do with genetics. Autism is not genetic. It is caused by mercury.

  3. Lisa says:

    Actually, I think it means that the threshold for diagnosis with autism is higher for girls than boys. That is, a boy is MUCH more likely to be diagnosed with autism than a girl given the same symptoms.

    I’ve had a dozen autistic boys in my mainstream classes over the years but only one girl.

  4. Lisa says:

    John Best is wrong.

  5. whatever says:

    Actually, John Best it correct. There exists numerous studies and much research to support John Best’s statement concerning testosterone and mercury. There all exists much research and many studies showing elevated testosterone in individuals with asd (not just males, but females as well). Of course rather than take my word for it or simply blindly believe Lisa, the readers could easily look for themselves. It is not hard to find. May the search engines begin……..

  6. Lisa says:

    Mercury has long been out of vaccines and yet, autism rates are still increasing. Clearly NOT the source of the problem.

  7. ikanclosen says:

    The only reason autism rates are rising is because of the cases that went undiagnosed for years and are now just being categorized as autistic. (Hence the increase of teens being diagnosed with some forms of autism.) Also the awareness of autism, especially in the milder cases, are now just coming forward and being diagnosed as autistic where as before they were just “learning disorders.” I belive the hard core autistic cases, where there is little eye contact, addictive behavior, unable to reason, and withdrawal from our world, have actually dropped substantially, while the borderline cases have increased for the reasons stated above. There is no doubt in my mind that thymerisol, the mercury binder in MMR shots, is the cause.

  8. heatherturgeon says:

    @slart: i read that paper too, suggesting why traits of autism were adaptive to our ancestors, for example, the ability to be alone and focus on one task – in this case finding food, etc. (is this the one you mean?)
    @Lisa, do you mean that you think boys and girls could exhibit the same symptoms but we only recognize it as problematic in boys? or that there’s a gender bias in diagnosis?

  9. Slartibartfastibast says:

    @ikanclosen

    It’s that “no doubt in my mind” part that has me worried. You clearly don’t understand the topic at hand (nobody entirely does yet), but you feel like you can still express total certainty. Just from an epistemological point of view that makes no sense… Please, trust me, there isn’t a conspiracy. People like to think that there’s someone “at the wheel” when stuff is big, scary, and uncertain. Even if we think that the people “running the show” (like all those greedy pediatricians, they must be in it for the cash!) are out to get us, it’s comforting to feel certain that you at least understand what’s going on. Sometimes that’s the case. Not here. Autism is very, very genetic. Twin studies have essentially proven this.

    I get the impression that many people don’t understand why vaccines are a necessary component of modern existence. For starters, the average human lifespan was 33 in the paleolithic era, 25-30 in pre-Columbian North America (so, Native Americans lived that long on average. I don’t care if this doesn’t agree with your preconceived notions. It’s true. Google it.), and 28 in ancient Greece and Rome.

    When people move to cities, the rate of encounters with people increases (you might run into 50 new faces in a day rather than 5). Diseases spread through contact, and adapt (i.e. become newer and more virulent) at a rate that grows with the rate of new hosts/transfers. In a city, YOU don’t just run into 50 times as many people (each with a probability of transmitting a disease), EVERYONE runs into 50 times as many people. This means that a linear increase in contacts per day becomes an exponential increase in total disease transfers (and, hence, potential adaptations) per day. This means that cities, until recently, were major sources of highly communicable human diseases. Modern sanitation and hygiene helped slow the process, but you need to have herd-immunity if you want to prevent the geographic spread of a disease. This requires vaccinations.

    Also, even if you think everything I’m saying is total BS, you should still vaccinate your kids: http://www.youtube.com/watch?v=RfdZTZQvuCo

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