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Science interrupted ... by Neanderthals

This time on Science interrupted I’m going to talk to you about how my adventures in science were interrupted by neanderthal DNA. And why you, like me, may have your neanderthal ancestors to thank for why you don’t get sick.

Neanderthals are the closest relative to humans when we look at our family tree1, having close to 99.6% of their DNA in common with our own. For a while, scientists considered our species to be completely separate from theirs. But more recent research has suggested that homo sapiens (us) and Neanderthals were closer than that - in fact, they most likely fell in love, got married, and had babies together. OK, that’s a little bit of a dramatization of what probably happened, but homo sapiens and neanderthals did have children together2–4. This is why many people alive today, including yours truly, have Neanderthal DNA in their DNA (side note: 23 & Me gives an estimate of this in their genetic profiling, which is how I found out that I have more Neanderthal DNA than 95% of 23 & Me users. Which, when we look at how much of my DNA is Neanderthal in origin, comes out to be less than 2% of my total DNA. Guess I’m just human after all).

So why the hangup on Neanderthal DNA? Last week I was alerted to some recent research suggesting that Neanderthal DNA may actually be playing a role in if people get sick5. What’s cooler, or scarier depending on your outlook, is that this Neanderthal DNA seems to play a role in the severity of COVID-19 cases6,7.

DNA from Neanderthals, people we often consider to be “primitive” losers that homo sapiens outcompeted, actually plays a role in determining how your body and immune system react if you contract COVID-19. How freaking cool is that?!

This research suggests that this Neanderthal DNA is found on different chromosomes (chromosomes 3 and 12) and that these different sections of DNA have different effects. The DNA on chromosome 3 seems to be associated with susceptibility to severe COVID-19 symptoms, and the DNA on chromosome 12 seems to be associated with resilience to severe COVID-19 symptoms. While COVID-19 is a hot topic in research right now, it isn’t the only disease that these DNA regions influence our susceptibility or resilience to8.

But the genetic variants on these chromosomes aren’t equally distributed across all people - the region on chromosome 3 seems to be more prevalent in Southeast Asians and rarer in Europeans. The region on chromosome 12 seems to be more prevalent across the board -- between 25 and 35% of people of Eurasian descent (meaning those of European or Asian descent) have this DNA region.

It is pretty clear that there are some huge real-world implications of this research -- when COVID-19 becomes an endemic human disease9,10 like ebola, malaria, or chickenpox, doctors will be able to perform simple genetic tests to determine which patients might be likely to experience severe COVID-19. Modern technology for the win.

But what I think is even cooler is that this research shows some pretty big genetic conflict in action. Our immune systems function to keep us healthy, with our DNA determining how effective our immune systems can be. But, here we have evidence that certain parts of our DNA may actively be working to reduce the effectiveness of our immune systems -- our genes are quite literally fighting it out to determine exactly how well our bodies function. While this isn’t exactly the kind of genetic conflict I study, this is a clear example of why scientists, doctors, and the public need to be aware of how powerful genetic conflict can be. Most of the time, genetic conflict leads to normal growth, development, and health. But sometimes, like in this example, genetic conflict dramatically influences the likelihood of someone living or dying.

In my downtime, I have a bad habit of perusing new mom groups on Facebook. Sometimes you find some great advice, other times it is like being unable to stop watching a train wreck as it happens (it is in these moments that my husband tells me to put my phone down and do literally anything else with my life). One of the bigger train wrecks I’ve seen recently is that pregnant and nursing moms are proclaiming that they will not get a COVID-19 vaccine because it is what’s “best” for their babies since we don’t know what could possibly happen to babies exposed to the vaccine.

That couldn’t be further from the truth.

While we don’t know if the virus that causes COVID-19 can be passed through breastmilk, current research shows that the antibodies that fight COVID-19 are passed through breastmilk11,12 -- this is why the CDC and WHO recommend that mothers who are diagnosed with COVID-19 continue to breastfeed their infants (see my previous post about maternal antibodies if you want a refresher about why antibodies are passed to infants through breastmilk13). What this also means is that if you are COVID-19 negative and get the vaccine, then your body will make and pass COVID-19 antibodies on to your nursing infant.

The same thing happens in pregnant women. While it is much harder and ethically complicated to do studies on pregnant women, some opportunistic situations let us speculate about what is going on. We now know that fetuses can be born with COVID-19 if their mother is infected14. But, more importantly, fetuses can be born with COVID-19 antibodies if their mother is COVID-19 negative but has received at least one dose of the COVID-19 vaccine15. This isn’t a controversial statement and it is why doctors tell expecting women to get a flu shot and DTaP vaccine during pregnancy - mom’s body can take the vaccine, make antibodies, and pass them to the fetus through their glorious placenta, thus ensuring that the fetus is protected against these diseases without ever having to experience them firsthand.

If you’ll allow me to stand on my soapbox for a moment, this is another reason why you should get your COVID-19 vaccine when you are able. To get this disease under control, and during this global pandemic into an endemic disease, we need to vaccinate and follow public health guidelines. Scientists know what they are doing, and while it may suck to miss out on all of our non-pandemic activities, they have made these guidelines to try to get us back to normal as quickly as possible. It isn’t just about protecting you (even though getting the vaccine does protect you) because we are all in this together.

Stay curious my friends,

JDA

In case you are interested, here are some of the articles that I read and thought about while writing this.

1. Anderson, C. The Secret Life of Neanderthals - How our closest cousins lived, died, and still exist today - Science Over Everything. http://scienceovereverything.com/2018/03/08/the-secret-life-of-neanderthals/ (2018).

2. Interbreeding. https://humanorigins.si.edu/evidence/genetics/ancient-dna-and-neanderthals/interbreeding.

3. Fu, Q. et al. An early modern human from Romania with a recent Neanderthal ancestor. Nature 524, 216–219 (2015).

4. Villanea, F. A. & Schraiber, J. G. Multiple episodes of interbreeding between Neanderthal and modern humans. Nat Ecol Evol 3, 39–44 (2019).

5. The Economist. DNA from Neanderthals affects vulnerability to covid-19. https://www.economist.com/science-and-technology/2021/02/24/dna-from-neanderthals-affects-vulnerability-to-covid-19 (2021).

6. Zeberg, H. & Pääbo, S. A genomic region associated with protection against severe COVID-19 is inherited from Neandertals. Proc. Natl. Acad. Sci. U. S. A. 118, (2021).

7. Zeberg, H. & Pääbo, S. The major genetic risk factor for severe COVID-19 is inherited from Neanderthals. Nature vol. 587 610–612 (2020).

8. Donahue, M. Z. New Clues to How Neanderthal Genes Affect Your Health. National Geographic (2017).

9. Phillips, N. The coronavirus is here to stay - here’s what that means. Nature 590, 382–384 (2021).

10. Torjesen, I. Covid-19 will become endemic but with decreased potency over time, scientists believe. BMJ 372, n494 (2021).

11. Pace, R. M. et al. COVID-19 and human milk: SARS-CoV-2, antibodies, and neutralizing capacity. medRxiv (2020) doi:10.1101/2020.09.16.20196071.

12. Breastfeeding and COVID-19. Bull. Acad. Natl. Med. 204, e140–e141 (2020).

13. Science interrupted ... by maternal antibodies. https://www.jessicadayers.org/blog/science-interrupted-by-maternal-antibodies.

14. Mehreen Zaigham, The Conversation. COVID found mutating inside a baby born with the virus, in a world first. https://www.sciencealert.com/covid-found-mutating-inside-a-baby-infected-before-birth-in-world-first.

15. Miller, A. M. A baby girl born to a partially vaccinated healthcare worker has COVID-19 antibodies. Business Insider (2021).

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