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  • Thanks to the National Institutes of Health's

  • National Human Genome Research Institute

  • for supporting this episode of SciShow.

  • [♪ INTRO]

  • The first time you visit a new doctor,

  • they'll probably ask about your family history.

  • Everything from heart disease to certain cancers

  • to type 2 diabetesif one of your close relatives has had it,

  • they want to know.

  • And for good reason.

  • These family histories can give your doctor a sense

  • of whether you, too, might carry an increased genetic risk

  • for those diseases.

  • Not a complete sense, thoughbecause it turns out

  • family history doesn't tell you everything about the risks

  • that can be hidden in your genes.

  • And to understand why, you have to look at

  • the complex genetics of disease.

  • Sometimes, understanding disease risk

  • even beyond family historyis pretty straightforward,

  • because in some cases, a mutation in a single gene

  • can greatly increase your risk for a given disease.

  • Take the genes BRCA1 and BRCA2, for example.

  • Variants or mutations in those genes can give you a

  • 45 to 65% chance of developing breast cancer

  • at some point in your life.

  • Not 45% increased risk, 45% chance.

  • That's no jokeand something your doctor can help determine based on your family history.

  • They might recommend that you take a genetic test,

  • for example, if you have relatives with BRCA mutations

  • or who have had breast cancer.

  • But most people who get breast cancer

  • don't actually have those mutations.

  • They're only present in a very small percentage of the population.

  • Researchers used to chalk this up to a hard and

  • fast line between sporadic and hereditary disease.

  • Hereditary disease is one that you, you know, inherit.

  • A sporadic one isn't inheritedit's seemingly caused by

  • something in your environment, or something else.

  • Except that distinction is starting to break down

  • the more we learn about our genomes.

  • See, sometimes a single gene can confer

  • a huge risk all by itselflike BRCA1 or 2.

  • Other times, though, it's more like a thousand little cuts,

  • because lots of genes are involved in increasing

  • your disease risk.

  • Basically, a large number of gene variants each contribute

  • a teeny tiny amount to your risk of heart disease,

  • cancers, or other conditionsand,

  • the more of them you inherit, the greater your risk.

  • That's true even if your parents or grandparents never got sick.

  • So from the point of view of your family history,

  • it wouldn't seem like you're at riskeven though you are.

  • We can detect the genetic part of these many-gene

  • or polygenic diseases, though, now that we have

  • the sequence of the human genome.

  • One of the most important tools that whole genome

  • sequencing has given us is a type of study called

  • a genome-wide association study, or GWAS for short.

  • These studies examine genetic data from a huge number

  • of peoplethough, usually, there's no need

  • to sequence their entire genome.

  • Instead, researchers look for genetic variants

  • called single-nucleotide polymorphisms, or SNPs.

  • These SNPs aren't necessarily the variants causing

  • an increase in your disease risk, mind you.

  • They may just happen to lie in close proximity

  • to the ones that did, and because of that,

  • they're inherited alongside them.

  • By surveying for SNPs and inheritance patterns

  • in these large studies, we can finally see the thousand cuts

  • metaphorically speaking of course.

  • Andthousandsisn't an exaggeration.

  • Sometimes, we can identify literally thousands

  • of variants associated with genetic risk.

  • GWAS have identified genomic variants that can

  • contribute a tiny amount to your risk of a given disease,

  • even when you account for your lifestyle and your environment.

  • Though, figuring out just how at-risk a person

  • is of developing a given condition is not as simple

  • as adding up the risky gene variants.

  • Risk variants can synergize or cancel each other

  • out in complex ways, so researchers have to do

  • some heavy-duty math.

  • The result of this math is something called a polygenic risk score:

  • a number that assigns a person's risk for a given disease

  • based on the combination of genomic variants they have.

  • And these numbers are helping us to understand

  • the genetic nature of diseases we used to think were sporadic.

  • Consider a study published in 2018 in the journal

  • Nature Genetics, for example.

  • They calculated a polygenic risk score for

  • coronary artery disease and found that 8% of their

  • study population had a three-fold greater risk

  • compared to the rest.

  • That's twenty times more at-risk people than

  • previous research could identify based on looking for

  • known familial forms of the disease.

  • Or, consider another 2018 study which calculated

  • a polygenic risk score for aggressive prostate cancer.

  • In that study, the polygenic risk score outperformed

  • family history and widely-used screening tests in

  • predicting who would develop prostate cancer,

  • and at what age.

  • Point is, these scores could be calculated

  • long before a person develops the actual illness

  • maybe even at birth.

  • Then, those patients could be encouraged to

  • practice healthier lifestyle habits, or given targeted drugs

  • because, like most things in genetics,

  • polygenic risk scores are not destiny.

  • Your lifestyle and environment still matter, a lot.

  • So tools like this could help us spot huge numbers of people

  • at risk of getting sick and then help them never get sick.

  • There's a huge caveat to how useful these

  • polygenic risk scores are, though.

  • You see, the people who have been studied in

  • GWAS so far are overwhelmingly of white European ancestry.

  • And that means, when polygenic risk scores

  • are calculated using existing data,

  • they're most informative for white folks.

  • Many scientists are aware that the field of genomics

  • has a diversity problem and are taking steps to fix it.

  • But such data are only now being collected.

  • Some researchers believe this diversity problem

  • is the single biggest obstacle to getting

  • polygenic risk scores into the clinic

  • where they can actually help people.

  • If that hurdle can be overcome, though,

  • these scores have the potential to help patients head off

  • diseases before they have a chance to manifest.

  • Which could be great news for lots of people.

  • And even before then, understanding how all these

  • genes work together in tiny ways will help us unravel

  • the intricacies of genetic diseases they help cause.

  • Thanks again to the National Human Genome Research Institute

  • for supporting this episode of SciShow.

  • If you're interested in learning more about the

  • human genome and the latest polygenic risk score research,

  • head to genome.gov or click the link in the description.

  • [♪ OUTRO]

Thanks to the National Institutes of Health's

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あなたの家系図ではわからないこと (What Your Family History Can’t Tell You)

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    林宜悉 に公開 2021 年 01 月 14 日
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