Genetics May Explain Why Autism Is More Common in Boys

By Carl Engelking | February 27, 2014 3:18 pm

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When it comes to developmental disorders of the brain, men and women are not created equal.

Decades of research have shown that males are at far greater risk for neurodevelopmental disorders such as autism spectrum disorder (ASD) than females. Boys, on average, are five times more likely to have autism than girls . What causes this disparity has largely remained unknown.

Now scientists have uncovered compelling genetic evidence to explain why the biological scales aren’t balanced.

According to a team of geneticists in the U.S. and Switzerland, it all boils down to what’s called the “female protective model.” This suggests that girls have a higher tolerance for harmful genetic mutations and therefore require a larger number of them than boys to reach the diagnostic threshold of a developmental disorder. With identical genetic mutations, then, a boy could show symptoms of ASD while a girl could show none.

But because the female mutation threshold is higher, when girls are diagnosed with ASD, they tend to fall on the more severe end of the spectrum.

Researchers believe the same dynamic could explain why more boys are diagnosed with ADHD, intellectual disabilities and schizophrenia. The findings were published Thursday in the American Journal of Human Genetics.

All in the Genes

Geneticists analyzed DNA samples from 16,000 boys and girls with neurodevelopmental disorders. They found that, on average, females diagnosed with ASD had 1.3 to 3 times more harmful genetic alterations than males diagnosed with the disorder.

The findings suggest that as the male brain develops, smaller and more subtle genetic changes can trigger autism spectrum disorders. Female brains require a greater number or severity of mutations before showing symptoms, so their symptoms tend to be worse.

“There’s no application in terms of treatment,” said study author Sébastien Jacquemont of University Hospital of Lausanne in Switzerland, but “it does help understand the inheritance dynamics in families.”

Jacquemont also studied some 800 families in which a family member was affected by ASD. He found that children were more likely to inherit gene mutations linked to autism from their mothers. Jacquemont says this may be because a male with a severe form of autism may have more trouble forming relationships and be less likely to have children. In contrast, the same genetic glitches in a female could go unnoticed, Jacquemont says, so that woman may be more likely to start a family and unknowingly pass the genes to her offspring.

Unclear Cause

The study doesn’t answer the most profound question surrounding the genetics of neurodevelopmental disorders: “What causes these disorders?” It’s still unclear which particular genetic glitches are responsible for different manifestations of developmental disorders. Or if genetic alterations are even passed down from parents, rather than simply appearing in children as they develop. Jacquemont is hoping to form larger cohorts to study which mutations put children at risk for ASD and other neurodevelopmental disorders.

Still, some researchers aren’t convinced that genetics are even the way to answer questions about neurodevelopmental disease. Irva Hertz-Picciotto, an epidemiologist at the University of California-Davis, told USA Today,

“Boys are swimming in measurably more testosterone than girls are. Some evidence suggests that social behaviors are in part determined by such early life exposures to sex steroids.”

Still, advances in the genetics of neruodevelopmental disorders could help families gain insight into whether their children are likely to inherit genetic markers associated with disorders like autism.

Image credit:  Zurijeta/Shutterstock

  • S. A. Hunt

    The older you get, the more genetic mutations start showing up in your reproductive system. Your old-ass testicles are creating messed-up DNA and it just gets worse and worse with age. Occam’s Razor, people.

    • Tyrel Kessinger

      Wait. Are you disagreeing with the article or what?

    • Kevin O’connor

      It’s coming from the female…WHo don’t have testicles…You might want to review a biology text before the next date night…I’m just sayin.

      • S. A. Hunt

        Something tells me you don’t understand how fertilization works, Kevin.

    • http://blogs.discovermagazine.com Linda Immler

      Or old-ass ovaries.

  • Reynardine

    That looks like a sex-linked trait to me.

  • disqus_DHydi6nJ7p

    I hate articles like this, I am a female with ASD, and even though it discusses ASD in females, it still has bias that would give someone the impression that females don’t have ASD as bad (in article is only speculating) so……this crap makes it harder for people like me to get help and our diagnosis taken seriously. I’m automatically labeled as rude even with disclosure of my diagnosis but if you have ASD the reality is you can never develop social skills like a normal person

    • Brandy Nolan

      It doesn’t say girls don’t have it as bad as the boys….in fact it says that girls tend to have worse cases than boys just later onset than boys.

  • Brandy Nolan

    Before I comment, let me give some personal back ground….. My 12yr-old daughter has early onset childhood schizophrenia. I noticed her having issues around age 2 but the doctors kept saying I was wrong and kids don’t get it that early, especially girls!…they would say autism or a variety of other issues, but I knew what it really was. They tried to say only boys get it before puberty, which is a flat out lie! Just because she wasn’t being violent and only showing the positive symptoms, the majority of the time…the docs said she should be more violent than she is.

    Soooo……here is my thoughts on this article.

    Doctors tend to say that autism & schizophrenia rates are higher in boys verses girls, but once it is noticed in girls the cases tend to be more severe than their boy counterparts. In reality, I think the case numbers and age of onset are really about the same in both sexes. Doctors tend to notice theses issues in boys at an earlier age than in girls because girls can hide it better by retreating into themselves instead of being as hostile or violent. All the other cognitive symptoms are presenting both sexes at the early age but the girls get ignored for longer which makes their cases worse in the long run due to lack of treatment

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