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NOVA ScienceNOW

Personal DNA Testing

  • Posted 07.02.08
  • NOVA scienceNOW

Host Neil deGrasse Tyson submits his spit for analysis in order to get a personal genetic profile that will predict his chances of contracting one of several serious diseases. But would you? Several companies now offer such a service for a fee that can range upwards of several thousands of dollars. How do such tests work and how valid are they? Furthermore, what do you do if you get bad news or good news? Before long, everyone will be able to sequence his or her entire genome. The hope is that doctors may one day be able to use our genomes to predict who is likely to get sick and what to do to prevent it. But this new era will have to wait until scientists fully untangle the web of genetic and environmental factors that cause most human disease.

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Launch Video Running Time: 12:35

Transcript

Personal DNA Testing

PBS Airdate: July 2, 2008

NEIL deGRASSE TYSON: Hi, I'm Neil deGrasse Tyson, your host of NOVA scienceNOW.

It seems like every week, scientists uncover more secrets of our DNA, revealing how our genetic code can shape and influence our lives. And for some, this is scary, raising fears that insurance companies or employers might see our genetic profile and hold it against us.

BUREAUCRAT NEIL: Well, Mr. deGrasse Tyson, I've seen your genetic profile, and it's not pretty. In fact, you're much too much of a genetic risk for us.

NEIL deGRASSE TYSON: But some say that knowing our genetic risk for disease will actually lead us to longer, healthier lives.

DOCTOR NEIL: Well, Neil, I've reviewed your genome. Here are my recommendations. And we've prepared a bottle of vitamins especially for you.

NEIL deGRASSE TYSON: Well, thank you!

DOCTOR NEIL: Live long and prosper.

NEIL deGRASSE TYSON: So what can genetic testing actually tell us about our chances for a long and healthy life? And will that knowledge help us or hurt us?

Can you imagine a simple test that tells you how healthy, or not, you'll be in the future: if you'll get cancer, gradually lose your memory, or be suddenly stricken by a heart attack? Sounds like something out of science fiction, but could this be possible today?

Judging from the headlines, you might think so. New companies have just burst onto the scene, proclaiming the dawn of a new age of personalized genetic testing.

DIETRICH STEPHAN: We're at the beginning of a medical revolution. So this is where the DNA arrives.

NEIL deGRASSE TYSON: Dietrich Stephan is a founder of Navigenics, which specializes in medical testing. For a fee of $2,500, they'll screen your DNA and tell you your genetic risk of getting a variety of scary diseases.

DIETRICH STEPHAN: We're testing an individual to provide them a snapshot of how genetically loaded they are so that they can potentially reduce their risk. And we want to do that across the entire population.

NEIL deGRASSE TYSON: The entire population getting their DNA scanned? It sounds a little like the movie GATTACA, where, from birth, everyone's destiny is foretold by their genes.

NURSE (GATTACA Film Clip): Neurological condition, 60 percent probability; manic depression, 42 percent probability; attention deficit disorder, 89 percent probability; heart disorder, 99 percent probability. Life expectancy: 30.2 years.

MOTHER (GATTACA Film Clip): Thirty years?

NEIL deGRASSE TYSON: I wondered what was lurking in my DNA, and Navigenics agreed to test me for free. There was just one thing I needed to do: spit.

Quick start guide.

ELISSA LEVIN: You have agreed to provide us with a saliva sample and...

NEIL deGRASSE TYSON: Spit.

ELISSA LEVIN: Spit.

NEIL deGRASSE TYSON: Looks dangerous.

ELISSA LEVIN: It's a couple of millimeters.

NEIL deGRASSE TYSON: Biohazard!

ELISSA LEVIN: Saliva is the most painless way to collect a sufficient sample.

NEIL deGRASSE TYSON: So you're telling me you want me to spit into a cup.

ELISSA LEVIN: Takes about five minutes.

NEIL deGRASSE TYSON: Five minutes of spitting.

ELISSA LEVIN: Correct.

NEIL deGRASSE TYSON: I'm thinking of pastrami on rye with provolone, bag of potato chips...

Luckily, it turned out I'm pretty good at salivating.

Thinking of a caramel candy bar...

Took me 90 seconds. My spit then traveled to a lab in California, where they extracted and analyzed my DNA.

DNA is made of long chains of four chemicals, best known by their initials: A, C, G and T. There's about six billion of these letters in the human genome, but reading every one is painstaking and expensive. So the latest tests look for things called "SNPs," short for single nucleotide polymorphisms.

DIETRICH STEPHAN: So, a SNP is really any position in the genome where there is variation between individuals in the population.

Nearly all of our DNA is exactly the same from person to person, but there are about three million spots where a single letter difference will commonly show up. Each of those spots is a SNP. It's just one letter, and, in most cases, we don't know exactly what it does.

You might have a C at one position, and I might have a T. We're both alive. We both have arms and legs and noses and brains and totally functional.

But those subtle variations are what make you and I unique and different. But it's also what predisposes individuals, subtly, to these common diseases.

NEIL deGRASSE TYSON: So which SNPs do I have, and what can they tell me about my health?

To find out, the DNA I provided in all that spit is squirted onto a silicon gene chip which holds millions of tiny fragments of reference DNA to compare with mine. Wherever a strand of my DNA fits with the sample DNA, the two will link and light up, revealing exactly what letters I have in certain spots.

So we're looking at my actual...

DIETRICH STEPHAN: This is your actual genome. And what you can see...

NEIL deGRASSE TYSON: As represented on this chip?

DIETRICH STEPHAN: Correct.

NEIL deGRASSE TYSON: The bright white spots reveal my SNPs.

Now what Navigenics will do is compare them to the SNPs of people with certain diseases. If I have particular SNPs in common with them, then I'm more likely to get those diseases.

Stephan believes that if my SNPs put me in the group more likely to get a disease—like diabetes, for example—I'll be more motivated to adjust my lifestyle and lower my risk.

It's a nice idea, but will it work?

DAVID ALTSHULER (Massachusetts General Hospital): I don't think we should tell anyone that this will help their health, because we really have no idea.

NEIL deGRASSE TYSON: Geneticist David Altshuler has serious doubts about the current value of this kind of DNA test.

DAVID ALTSHULER: It might help their health, it might do nothing to their health, and it might hurt their health.

NEIL deGRASSE TYSON: But how could a DNA test hurt your health? Well, take the case of Alzheimer's disease. There's a gene that works inside the brain, and one version of this gene can lead to Alzheimer's disease in old age. If you look at this SNP in your DNA and you have a G right here, there's a strong chance you'll have that dangerous version of the gene. If you have two copies of the G, one on each chromosome, your risk of getting Alzheimer's, though not 100 percent could be 10 times higher than average.

So what would you do with news like that?

RUDOLPH E. TANZI (Massachusetts General Hospital): There's a minority of people who...it won't bother them at all what their genetics are. They just live their lives, say, "I don't care." But I worry about the other side of the bell curve, those who get genetic information. They look fine when they get it, and then they go home and freak out, or, in some cases even, you know, may commit suicide.

NEIL deGRASSE TYSON: Even James Watson, who deciphered the structure of DNA and recently had his entire genome sequenced, did not want to know if he had the high risk version of the gene called "ApoE4."

Alzheimer's expert, Rudy Tanzi can't blame him. Tanzi strongly discourages most people from testing for ApoE4.

RUDY TANZI: It needs to be emphasized that whether you inherit one or two copies of ApoE4, you are not guaranteed to get Alzheimer's disease in your lifetime. So it just doesn't make a whole lot of sense to do an E4 test for Alzheimer's disease, given that it's not a reliable predictor for the disease.

NEIL deGRASSE TYSON: This Alzheimer's test is so controversial, some genomics companies won't even offer it, but Navigenics does.

I thought long and hard about whether I wanted to hear my status, even if I couldn't do anything about it, and decided to find out. I'm a little worried, but I, kind of, think that I'd rather know than not know. Because I can use that information to adjust how I might live going forward.

Finally, the moment of truth arrives.

Have you seen them yet?

ELISSA LEVIN: Well, we review everything.

NEIL deGRASSE TYSON: That's a yes.

For about 10 diseases, Elissa Levin, Navigenics' Director of Genetic Counseling, gave me two numbers: first, an American man's average lifetime risk of getting a disease, and then my genetic risk, based on how many good or bad SNPs I had.

So, I'm looking here. Obesity, 22 percent?

They say my risk of becoming obese is 22 percent, while the average risk for males in the population is 25 percent.

ELISSA LEVIN: So you're just under the population average.

NEIL deGRASSE TYSON: I'm a little less likely...

ELISSA LEVIN: You're a little less likely, based on your genes.

NEIL deGRASSE TYSON: So, heart attack?

ELISSA LEVIN: That's about 52 percent.

NEIL deGRASSE TYSON: Fifty-two? And I'm coming in...?

ELISSA LEVIN: At about half of that.

NEIL deGRASSE TYSON: About half of that.

But what about Alzheimer's, do I have a G in those dangerous spots? Nope, the test said I had an A on both chromosomes.

This tells you I probably don't have that gene.

ELISSA LEVIN: I have to say this is a pretty stellar profile.

NEIL deGRASSE TYSON: But what's this? It looks a little high.

And so, prostate cancer: 17 percent in the general population, and I come in at 20 percent.

ELISSA LEVIN: Right.

NEIL deGRASSE TYSON: So, remember, these SNPs cannot tell you for sure if you'll get these big common diseases.

DAVID ALTSHULER: First of all, they're only clues. We don't know what they mean. We don't know all the mutations in those genes. We certainly don't know how they work biologically. We have no clue what they mean clinically. We have no idea how they would affect the treatment you should take.

NEIL deGRASSE TYSON: Even if we could pinpoint all the genes that contribute to the big common diseases, that still wouldn't be enough.

We know, from studying identical twins, genes can't be the whole story. Even with the exact same DNA, one twin might get cancer, the other won't. And we still don't know why.

RUDY TANZI: For the majority of age-related diseases that, you know, challenge healthy aging, we're still in process of figuring out the genetic factors, never mind figuring out how they interact with the environment or even what the environmental factors are. These are early days.

NEIL deGRASSE TYSON: For now, skeptics say these tests may be no more predictive than a good family history.

But what if we could find a cheap way to read, not just SNPs, but the entire genomes of many people, as they're trying to do here at Harvard Medical School? If we combine those with personal histories, intimate details of our habits and behaviors, could we get closer to overcoming the big killer diseases?

DAVID ALTSHULER: The more sequence we capture in people with disease, 'til it's complete, and different numbers of people in different populations, we will, I am entirely confident, learn about disease and human biology, and we'll learn about human history. We're going to learn about ourselves, so...knowledge itself can be challenging.

Credits

Personal DNA Testing

PBS Airdate: July 2, 2008

Edited by
Dick Bartlett
Written, Produced and Directed by
Julia Cort

NOVA scienceNOW Credits

Executive Producer
Samuel Fine
Executive Editor
Neil deGrasse Tyson
Senior Series Producer
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Supervising Producers
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Senior Editor
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Sputnik Animation
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For Lone Wolf Documentary Group

Executive Producer
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Production Manager
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Archival Material
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National Human Genome Research Institute
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Special Thanks
Affymetrix
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Ben Fry
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Icelandic Tourist Board
Maryam M. Khani
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Neil deGrasse Tyson is director of the Hayden Planetarium in the Rose Center for Earth and Space at the American Museum of Natural History.

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NOVA scienceNOW is a trademark of the WGBH Educational Foundation

This material is based upon work supported by the National Science Foundation under Grant No. 0638931. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

NOVA scienceNOW is produced for WGBH/Boston by NOVA.

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IMAGE:

(DNA and test tube)
© Zmeel Photography/iStock Photo

Sources

Links

HHMI Online Companion
www.hhmi.org/resources/science_now/personal_dna.html
The Howard Hughes Medical Institute provides an extensive collection of resources on genetic testing in its online companion to this segment of NOVA scienceNOW.
More on HHMI and its partnership with NOVA

National Human Genome Research Institute
genome.gov
Check out fact sheets with information on genetic mapping, cloning, and more, or watch a video about the value of family history in preventative medicine.

Medline Plus: Genetic Testing
www.nlm.nih.gov/medlineplus/genetictesting.html
Investigate what genetic testing involves and make sense of scientific terms with a helpful glossary.

Human Genome Project Information
www.ornl.gov/sci/techresources/Human_Genome/home.shtml
Learn the details of a 13-year international effort, completed in 2003, to identify tens of thousands of genes in human DNA.

Personal Genome Project
www.personalgenomes.org
Find out what researchers at the Personal Genome Project are doing to make genome sequencing mainstream and affordable.

Genetic Privacy Bill
thomas.loc.gov/cgi-bin/bdquery/z?d110:HR00493:
This Library of Congress site provides the full text of legislation H.R. 493, which prohibits employment and health-insurance discrimination on the basis of genetic information.

Related Links