Your DNA is constantly mutating, and that’s a good thing

IRA FLATOW: Hi, this is Ira Flatow, and you’re listening to Science Friday. Right now you’re DNA is mutating. Yes, yours. Well, and mine too.

And no, I’m not giving you an early cancer diagnosis. Cancer and mutations obviously go hand in hand, but you may be surprised to that our bodily systems are rife with mutations. These errors and attempts to repair them are a key to understanding immune function, aging, and even how heart disease develops. In fact, gene mutations can even mitigate the harm caused by some inherited diseases.

My next guest is here to take us on a journey through the illuminating science of genetic mutations. Roxanne Khamsi is a science writer and author of the new book Beyond Inheritance– Our Ever-Mutating Cells and a New Understanding of Health. She’s based in Montreal, Quebec. Welcome to Science Friday. Welcome back.

ROXANNE KHAMSI: Thank you so much, Ira. It’s great to be back.

IRA FLATOW: Nice to have you. Most of us think about our DNA as, it’s static, it’s stable, kind of like a personal ID number. How should we be thinking about how our DNA changes over the course of our lives?

ROXANNE KHAMSI: So I was taught the same thing. I was taught that the DNA I inherited from my mother and my father is the same in all of my cells. And what I discovered about eight years ago was that’s not the whole picture and that scientists right now are uncovering that each human body is a landscape of genetic diversity and that our DNA is dynamic. It’s not static.

In fact, scientists estimate that if a person reaches 100 years old, a single white blood cell will have around 3,000 mutations that are not found in the rest of their body. So this is the new understanding of genetics I really feel is important, that our DNA changes over time.

IRA FLATOW: Why are mutations so rampant, then, in our cells?

ROXANNE KHAMSI: So part of this has to do with the fact that we are a collection of cells. We all start as a single cell for the first 24 hours after we’re conceived. And then by the time we reach adulthood, we’re around 30 to 40 trillion cells. And that’s not counting the 30 trillion cells in our gut microbiome that are microbial cells.

And there’s a lot of turnover to maintain this mass of cells that we are. Every time a cell divides, it’s trying to copy its DNA. And sometimes it makes errors. And when it does make errors, those mutations, those DNA mistakes, stick around in all the subsequent cells.

And on top of that, there’s just regular wear and tear that happens inside the cells of our bodies. So DNA breaks, and when that gets fixed, sometimes errors are introduced there as well.

IRA FLATOW: In your book, you use this metaphor of the mosaic to describe how our cells grow and change over time. Why mosaic?

ROXANNE KHAMSI: So I think it’s important to understand that the cell in my toe, for example, is not the same as the cell in my brain, genetically. And I like the idea of having a mosaic in mind because, when we think about a mosaic, those pieces form a coherent whole. But when you look at them individually and compare them, there are slight differences.

And I think that you can look at the human body the same way. Our cells are similar in that they’re all working to make us sing a song or lift a spoon to our mouth. But at the individual level, there are differences, and some of those differences can be meaningful.

IRA FLATOW: When we think of genetic mutations that cause disease, I think we’re often thinking about the ones that get passed down from our family tree, like Tay-Sachs or sickle cell. Is there a difference between inherited mutations versus the ones that develop over the course of our lives?

ROXANNE KHAMSI: It’s a really interesting question, and I think this speaks to why I wrote this book. I want people to understand that genetic disease is not always something that is inherited. It’s something that can spontaneously develop in us.

Now, if you inherit a mutation, say, for sickle cell or cystic fibrosis or Tay-Sachs, that mutation is found in all the cells of your body. But if a spontaneous genetic DNA error occurs, it is only in some of the cells of your body, going back to that idea of mosaic. That being said, you can still develop a genetic disease that is full blown if it develops early enough in your life.

Also, if it develops later, but in important cells, say, in your brain, you could have a genetic disease that affects you profoundly. So we’re talking about scientists now understanding that spontaneous DNA errors can cause epilepsy, autism. There’s a long list of common diseases that can be caused by genetic errors that spontaneously occur.

IRA FLATOW: Interesting. I think many of us are familiar with the term “epigenetics,” the idea that our environment, our life experience can have effect on how our genes are expressed. Is that different from the mutation you’re talking about in our DNA?

ROXANNE KHAMSI: Yeah, definitely. So what I tell people that I’m interested in this, they often ask, so are you writing about epigenetics?

IRA FLATOW: Right, right.

ROXANNE KHAMSI: Yeah, I have to shift their thinking because I am interested in epigenetics. I write about epigenetics. But I really wanted to focus on the actual sequence changes that happen. So epigenetic markers sit on top of the DNA, but what I’m talking about here are actual changes to those three billion nucleotides that make up the human genome in each of our cells.

IRA FLATOW: Yeah, yeah. Let’s get into some specifics, if you might. You talked about the white blood cell before. You write about how blood cell mutations can lead to heart attack and stroke. I was kind of surprised that I had no idea mutations were at play here. What’s going on?

ROXANNE KHAMSI: Yes, definitely. This is one of the reasons I had to write this book because I was shocked– I learned about this about eight years ago– when I read that in The New England Journal in Medicine, they had a brand new paper suggesting that mutant blood cells were not only linked to cancer but, in some people that had no cancer, were doubling the risk of heart disease, stroke, all these cardiovascular diseases.

And I was just shocked because I’d never thought about mutation as causing these kind of diseases. It was completely new to me.

IRA FLATOW: Are these the kinds of mutations that happen spontaneously? Or does our lifestyle contribute to these mutations?

ROXANNE KHAMSI: So some of it happens to just be time. Over the course of our lives, we are more likely to pick up mutations that cause these large populations of mutant blood cells to start growing within us. And so by the time somebody is 70 years old, there’s about a 10% to 20% chance that you have a substantial number of these mutant blood cells in your body.

But there’s also some interesting research looking at how things like getting good sleep might reduce your risk of these mutant blood cells rising in your body. And they’ve actually also tried to study what happens to astronauts in space, whether that extra radiation that they’re exposed to might also contribute to their risk of these mutant blood cells.

IRA FLATOW: How do mutations play a role in how the immune system functions?

ROXANNE KHAMSI: I think this is one of the most provocative things I’ve learned. So we tend to think about mutation as something bad. We’ve talked about cancer. We’ve talked about all sorts of genetic diseases.

But there is a necessity of mutation happening in our bodies. So if we don’t mutate, we can’t defend against the viruses and bacteria that try to infect us. People that can’t mutate their immune cells have a disorder called hyper-IgM syndrome, and they’re at extreme risk of opportunistic infections. They have basically compromised immune system and require all sorts of treatments, bone marrow transplants.

So we are very lucky, you and I are very lucky that our immune cells mutate to defend ourselves against bacteria and viruses in our environment.

IRA FLATOW: What about vaccines? Do they cause mutations of our DNA? This is one of the big anti-vax scare tactics. They will change your DNA.

ROXANNE KHAMSI: Yes, they do change your DNA. So I want to back up for a second and say even getting sick changes the DNA of your immune cells because your immune cells are essentially playing the lottery. They’re trying to figure out if they can rearrange their DNA, whether they can come up with a new antibody, a new kind of shape of antibody that will bind and neutralize that virus or that bacteria that’s trying to make you sick.

Now, with vaccines, we’re essentially doing the same thing. We’re trying to nudge the mutational patterns in the immune system in order to come up with an antibody but to do so quicker to give it a shortcut. So yeah, a lot of people that are skeptical of vaccines or anti-vaccine will say, these mutate your DNA.

And I say, yes, it does. It’s like somebody saying, you’re wearing an ugly dress. And I’m like, yes, I am wearing an ugly dress. And I did–

IRA FLATOW: And that’s–

ROXANNE KHAMSI: –so on purpose.

IRA FLATOW: –a good think.

ROXANNE KHAMSI: Or I like this pattern. But yeah, so we use vaccines in order to evolve our immune cells to make better antibodies.

IRA FLATOW: Let’s talk a bit about cancer because we always associate cancer with mutations. How has our scientific understanding of how cancer changed as we’ve learned more about how it mutates?

ROXANNE KHAMSI: Yeah, you could say our understanding has evolved. So we used to think about cancer as the result of one or two genetic errors, and that was the pervasive thinking for a few decades.

What recently has been shown is that cancers are just rife with mutations. In certain types of cancers, like colorectal cancers, for example, there’s some theories that there’s like a big bang of mutations that happens early on that just seeds a huge amount of diversity.

So instead of thinking of a tumor as something that was the result of one or two genetic errors, we now think of tumors and malignancies as hotbeds of mutation. And the challenge then is to think about which of those mutations are driving the cancer and making it most resistant to treatment.

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IRA FLATOW: After the break, how genetic mutations can actually be a good thing. Stay with us.

And speaking of mutations not doing just harm, you write about how they actually can autocorrect some genetic disorders. How does that work?

ROXANNE KHAMSI: So yeah, I want people to understand that we need a revolution in our understanding of mutation. And part of that is I want to de-stigmatize the concept of mutation. It’s not always a bad thing.

So back in the late 1990s, for example, scientists found that there were these two boys in the New York area that were born with a type of immunodeficiency. They were supposed to live in a bubble essentially their whole life. And what they found, though, is that these two boys were defying any expectations.

Their immune systems were doing much better than the scientists expected. And when they looked closely, they found that there actually had been mutations that these boys had acquired that had corrected their inherited disorder. And it’s not the only example.

So there’s a disease called Fanconi anemia, and about 20% of people with that disorder actually start having blood cells that correct the disease that they have. And in 5% of those cases, they have enough that they start to progress towards just curing themselves. So it is like finding the answer within.

IRA FLATOW: That is really, really interesting. We’ve talked on this show before about DNA changing as we age. Tell me how this mutation process plays a role in aging.

ROXANNE KHAMSI: So as you and I are talking, as people are listening, our DNA is just picking up mutations. And some of these mutations will stick around for a while. And the idea is that, by the time we’re older, we’ve kind of just amassed a bunch of mutation.

Now, the idea is, what happens if we might be able to undo some of the mutation that we acquire? And I know that on this show you guys have talked about bowhead whales and how they have a vast amount of DNA repair enzyme, and this might be part of the reason they can live 200 years and longer. So the question is, can we maybe replicate some of the DNA repair in those long-lived organisms to improve our longevity as well?

IRA FLATOW: Interesting. I know there’s a huge anti-aging industry that is just itching to figure out the key to longevity and probably make a lot of money. Is this science at a place where we can identify the mutations that are responsible for aging? I mean, we all age. But what about the mutations that might be responsible for aging?

ROXANNE KHAMSI: It is, yes, super tantalizing to think about this as a new avenue to anti-aging treatments. But as you’re pointing to, there’s a lot of hype in this industry that happens, and we want to make sure that we don’t go too far in one direction without having a reality check.

I think the important thing to recognize is, as you and I have talked about, mutation can be a good thing. So if you try to globally slow it down, you might be doing a disservice to the body. You might be slowing down its ability to defend itself, perhaps.

IRA FLATOW: Right, right. I remember when the first human genome was sequenced in 2000. It ushered in a revolution in biology. But there was another technological advance more recently called single-cell sequencing. Please explain what that is, and how did that shape our understanding of cell mutations?

ROXANNE KHAMSI: For sure. So once you’re able to look at the body at the single-cell level, you can really understand at a granular level which cells are mutating and which ones aren’t. And you can really compare and contrast. If you really want to count, let’s say, what proportion of cells have a mutation, that single-cell sequencing is super helpful.

IRA FLATOW: How could this new understanding of mutations change how we understand human health? And what kinds of new treatments are possible?

ROXANNE KHAMSI: So I’m not a huge proponent of things like smoking, and I was talking to my son’s babysitter about why not to smoke. And then I was thinking about what I learned. And that’s if you smoke a cigarette, you have mutations that happen in your body.

But now scientists can see, thanks to these technological advancements, that smoking a cigarette causes different mutations from, let’s say, chewing tobacco. And I think what this points to is we’re going to now be able to dissect how behaviors interact with our DNA at a whole new level. And also so when we see a mutation has corrected an inherited disorder, we can go back and say, hey, can we develop a drug based on that mutation that can help other people that didn’t spontaneously correct in that way? And we’re finding that that actually is the path that some researchers are taking with liver disease already.

IRA FLATOW: Now, I know you’ve been writing about genetics and biology for a long time. Has writing this book changed how you think about the causes of illness and disease at all?

ROXANNE KHAMSI: I definitely think that writing this book has changed how I think about genetic disease. So when I started my career, when people talked about patients with genetic disorders, there was a lot of othering. They have a mutation. I don’t have a mutation. I’m safe. I’m OK.

It felt like people tried to create space between those people with genetic disease and those people without. And what I’ve really come to understand is that we are all mutants. There’s no othering.

We all have a lot of spontaneity in our DNA, and who knows what kind of mutations we pick up? So I think it’s kind of made me see a more universal process in our DNA. I think that’s really what’s changed in my perspective, if that makes sense.

IRA FLATOW: That does, and it’s very interesting. And I’m thanking you for taking time to be with us today, Roxanne.

ROXANNE KHAMSI: Thank you so much. I have so enjoyed our conversation.

IRA FLATOW: Me too. Roxanne Khamsi, science writer and author of the new book, Beyond Inheritance– Our Ever-Mutating Cells and a New Understanding of Health. She’s based in Montreal, Quebec.

This episode was produced by Shoshannah Buxbaum. If you have a question you want us to look into, please, yes, our listener line is always open. Give us a call at 1-877-4-SCIFRI. That’s 1-877, number four, SCIFRI. I’m Ira Flatow. Thanks for listening.

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