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  • [intro]

  • Scientists have been studying autism spectrum disorder for the better part of a century,

  • and yet, there's one thing they can't seem to figure out:

  • why the brains of people with autism develop differently.

  • But because it's more common in boys,

  • some researchers have long suspected that testosterone levels in the womb are the key.

  • The only problem is, their evidence has come up short.

  • Turns out they might have been looking at the wrong hormones.

  • Just this week, a team of scientists at the University of Cambridge

  • and the State Serum Institute in Denmark announced that they've identified a link between autism

  • and a different sex hormone: estrogen.

  • And while might sound like the complete opposite of what you'd expect for something more

  • prevalent in boys,

  • it actually lines up with our understanding of autism better than you'd think.

  • Autism spectrum disorder affects about every one in 59 children,

  • but even after correcting for underdiagnosis and misdiagnosis,

  • it's roughly three times more likely in boys than in girls.

  • Girls with autism also generally have fewer autistic traits than boys.

  • And all that may imply that there's some kind of connection between autism

  • and the physiological differences that generally come with a Y chromosome.

  • Some have even suggested that autism is basically what happens

  • when you take typically male neurological traits and dial them up to 11.

  • This is what's known as theextreme male brain theoryof autism.

  • Now, it's important to note that this doesn't mean that autistic people are super masculine

  • overall

  • it just means that they have more of the traits that you see more frequently,

  • on average, in the brains of men.

  • And the differences we're talking about are very small.

  • Studies consistently show that men and women are more psychologically similar than they

  • are different.

  • But there are some traits that, again,

  • on average are more common or more pronounced in the brains of people with a Y chromosome

  • or who identify as men.

  • And it does seem like these traits are amplified in people with autism.

  • To give one example,

  • the brains of men tend to have weaker connectivity in the brain's default mode network.

  • That's a group of brain regions that's most active when you're not focused on the

  • outside world.

  • And it turns out that both men and women with autism have even lower connectivity in this

  • region

  • than the average neurotypical man.

  • Because there does seem to be some merit to this extreme male brain idea,

  • researchers have suggested that the biological pathways involved in the development of typically

  • masculine traits might be at the root of autism.

  • And that all traces back to fetal sex differentiation:

  • the biological cues that lead to the development

  • of typically masculine or feminine traits.

  • So in recent years,

  • researchers have begun to look for clues to autism in fetal development

  • and the conditions fetuses experience in-utero.

  • And at first, many thought androgens

  • the hormones involved in typically male traits

  • might be to blame, which makes intuitive sense.

  • The thing is, studies on prenatal testosterone levels alone

  • which is arguably the most important androgen

  • have found no relationship between it and autistic features.

  • Then, in a study published in 2015,

  • Cambridge and Danish researchers found elevated levels of several sex hormones in the amniotic

  • fluid of male fetuses

  • that went on to develop autism.

  • And while that did include testosterone and another androgen,

  • it also included progesterone:

  • which got the researchers thinking maybe they needed to widen their scope.

  • Which brings us to estrogen.

  • Estrogen actually refers to a group of hormones

  • which includes estriol, estradiol, estrone, and estetrol

  • none of which were tested in that 2015 study.

  • And these so-calledfemalehormones are very important

  • for fetal development regardless of sex.

  • Estradiol, in particular,

  • contributes a lot to brain development.

  • It helps to form and prune neurons and synapses,

  • and it regulates the activity of the neurotransmitter GABA.

  • In the brains of people with autism,

  • synapse and neuron formation and GABA regulation are all atypical.

  • So it might make sense that estrogen levels in the womb

  • could play a role in the development of autism, too.

  • To find out, those same researchers returned to the amniotic fluid samples they used in

  • their 2015 study.

  • These initially came from The Danish Historic Birth Cohort:

  • a set of biological samples from more than a hundred thousand pregnant people collected

  • between 1980 and 2004

  • who were followed up with to monitor the children's health over time,

  • including whether they were diagnosed with autism.

  • The researchers ended up with amniotic fluid samples from 98 males with autism and 177

  • neurotypical males.

  • They then analyzed the samples for various forms of estrogen.

  • And lo and behold,

  • they found that elevated levels of estradiol, estriol, and estrone

  • were all associated with an autism diagnosis.

  • Estradiol had the biggest effect:

  • a rise in this hormone from the 25th to the 75th percentile came with an almost 50% increase

  • in the likelihood of autism.

  • That's a lot more of an effect than has ever been seen with androgens.

  • Now, it may sound strange that estrogen, of all things,

  • could lead to a so-calledextreme male brain.”

  • But remember, estrogens do a lot of different things to a developing fetus,

  • depending on the tissues and the development period.

  • And they're not exclusively a female thing.

  • In fact, maternal estrogen levels are higher throughout pregnancy

  • no matter what sex the fetus is.

  • What this study suggests is that high levels of estrogen,

  • at least at about 15 weeks gestation, might lead to differences in brain development.

  • As for why estrogen levels are higher at that time,

  • the researchers suggested the placenta may have something to do with it.

  • It acts as a hormone regulator between mom and fetus,

  • and it's the fetus's main source of estrogen.

  • Plus, placental issues and autism risk often go hand in hand,

  • and they also disproportionately affect male fetuses.

  • But why that is is unclear

  • and there's a lot we don't understand about the interplay

  • between mom, baby, and placenta when it comes to hormones.

  • So the researchers want to further untangle what's going on.

  • And all that said, the research didn't find that amniotic fluid hormones perfectly predict

  • autism.

  • That's probably because both genes and hormones are at play:

  • like, high levels of estrogen might interact with particular gene variants

  • to affect the way the brain forms.

  • Also, the researchers have made it clear they're not interested in making some kind ofscreening

  • testfor autism

  • as the lead researcher said, they want to understand autism, not prevent it.

  • One major drawback to this study is that it was only in male fetuses,

  • so it's unclear whether the findings hold true for everyone.

  • At the time,

  • the team simply didn't have enough samples to do these tests for female fetuses

  • because the prevalence of autism is so much lower in them,

  • but they hope to get those samples in the future.

  • And the findings are still correlational

  • there may be some as of yet unidentified factor

  • that impacts amniotic hormone levels and the likelihood of an autism diagnosis.

  • Still, it suggests that researchers may have overlooked key components

  • in the development of autism

  • by focusing on typicallymalethings like testosterone.

  • And they're going to have to look at everything

  • if they want to get to the bottom of this century-old mystery.

  • Thanks for watching this episode of SciShow News!

  • And a special thank you to our channel members.

  • Those are the people you see in comments or chats with those special badges

  • they've all committed to supporting this channel,

  • and we couldn't make episodes like this without that support.

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  • thank you so much!

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  • learn more.

  • [ outro ]

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エストロゲンと自閉症の意外な関係|サイゾーウーマンニュース (The Unexpected Connection Between Estrogen and Autism | SciShow News)

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    林宜悉 に公開 2021 年 01 月 14 日
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