Posts Tagged ‘heart attack’

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In the United States, around 735,000 people each year have a heart attack. In all, heart disease (and its complications, including heart attacks) kills 610,000 a year here, making it the leading cause of death in America and worldwide.

Preventing heart disease is a huge public health challenge. And right now doctors have good, but limited, options for finding out who is at greatest risk for it.

Doctors know that about half the risk for heart disease comes from lifestyle choices: how much, and what, a person is eating, how much alcohol they drink, if they smoke.

The other half is related to genetics, and it’s much harder to assess. You can ask a person about their family history of heart disease and can check for high blood pressure and obesity, which are also related to genetics. But up until the recent explosion in genetic science, it was hard to probe the genes themselves.

Last week, in the journal Nature Genetics, researchers at Harvard University and the Broad Institute published evidence that they can check out 6 million spots in a person’s genome to assess their risk for developing coronary artery disease, when the main blood vessel supplying the heart with oxygen gets clogged with plaque. It’s a precursor to a heart attack, when a clot cuts off blood flow to the heart, starving it of oxygen.

In the study, people who carried the greatest number of genetic variants suggestive of heart attack risk were three or more times likely to develop coronary artery disease than controls. The researchers argue that with this test, about one in 12 people could be identified as having a higher risk of heart attack based on their genetics alone.

“If you told me there was a genetic score that could identify 8 percent of the population with more than a threefold risk, I’d say, that’s amazing,” Robert Yeh, a cardiologist at the Smith Center for Outcomes Research in Cardiology, who was not involved in the study, says. Currently, the best commonly available genetic test for heart disease risk — which looks for a single gene linked to high cholesterol — can only detect increased risk in 0.4 percent of people.

“The big takeaway is that we can now capture the inherited component to heart attack risk with a single number,” Sekar Kathiresan, the Massachusetts General Hospital cardiologist and geneticist who led the study, says. With this new tool, Kathiresan hopes doctors could put those people at higher risk on cholesterol-lowering medications (statins) at an earlier age, or more easily persuade them to make lifestyle changes to lower their risk.

The new tool here is called a polygenic risk score, which you can think of as a tally of the tiny changes in your genome that are correlated with risk of developing a disease.

In the coming years, you’re going to hear a lot more about them. These scores, while increasingly helpful in some areas of medicine, come with a lot of caveats. Indeed, when you dig a bit deeper into this latest Nature Genetics paper, you find there’s a lot more work to do to validate polygenic risk scores for heart disease, so they will be useful and relevant to people around the globe. For one: This study was exclusively conducted with subjects in the UK of white European background. The predictions derived from this group do not necessarily transfer over to another. For this and other reasons, scientists skeptical of polygenic risk scores say they are not yet ready for the clinic — and wonder if they will ever be.

At the same time, it seems likely these polygenic risk scores are going to change the way we think about our health and our medical decision-making.

What’s a polygenic risk score?
Over the past decade, medical researchers have realized that our risk for many common conditions like heart disease and diabetes are not influenced by just one gene, or even a small handful of them. Instead, studies analyzing huge numbers of sequenced human genomes have found that there are hundreds of genes that work in constellation influencing our risk for diseases.

DNA is the recipe for our biology. But it turns out that recipe looks something like an M.C. Escher drawing, with a huge number of genes influencing life outcomes in hard-to-understand, hard-to-follow, interconnected ways.

That is, there can be hundreds of interrelated spots in the genome that are correlated with a person’s risk for heart disease, or raising or lowering their height by a millimeter. Scientists are getting better at identifying these spots in the genome that confer risk and are now trying to figure out if tallying up these genetic changes — in what’s known as a “polygenic risk score” — is useful in trying to predict, and prevent, disease. (They are also calculating them for behavioral traits like educational attainment.)

In developing polygenic risk scores, in many cases, genetics researchers often don’t know what the underlying genes do. All they know is that these genes are correlated with — which does not mean cause — the disease. “It’s pretty mindless,” says Cecile Janssens, an epidemiologist at Emory University who is critical of the hype of polygenic risk scores.

Proponents of polygenic scoring, though, argue that you don’t need to know what the genes are doing to make predictions off them.

“It’s all about getting a predictor and then repeating it in other groups,” Kathiresan says. “At the end of the day, I could just call it a magic number generator. It doesn’t exactly matter how I’m getting there, as long as it works in other groups equally well.”

That’s what happened in this latest paper. A polygenic risk score derived from huge genome-wide association studies predicted heart attack risk in nearly 300,000 people in the UK. (Read more about how scientists come up with polygenic risk scores here.)

How good is the prediction?
Because each change in the genome — called single nucleotide polymorphisms, or SNPs (pronounced “snip”) — confers such a tiny change in risk, adding more and more of them to the risk score yields diminishing returns. “We see this trend already for years — every new SNP that we discover has a smaller effect than we knew already,” Janssens, says.

In the recent Nature Genetics study, she points out, when the researchers increased the number of SNPs in their risk model from 74 to 6 million, the predictive power of the test only increased by a smidgen. Most of those SNPs have a predictive power of approximately zero.

Here’s a chart showing where the polygenic risk score for coronary artery disease matters most. Polygenic scores, like so many human traits, are normally distributed, meaning they follow the pattern of the bell curve. But a person’s risk for coronary artery disease really only starts to increase if they have the very highest number of SNPs that are correlated with heart disease risk. The top 8 percent of the participants had a three times greater risk of heart disease. The top 0.5 percent had five times the risk.

There are many caveats to this risk prediction, which the authors of the study acknowledge. One is that it’s currently unclear if predicting heart attack risk in this manner provides an additional benefit to the risk models derived from asking people simple questions about their lifestyle and family history. The researchers suspect it does, but they didn’t set up their study to test this question.

Another is that this risk model was developed and tested solely on people who had donated their medical and genetic information to the UK Biobank, which contains only genetic data of people of white, European ancestry. The predictive power of these tests is expected to diminish in people of African ancestry, Asian ancestry, and so on. Genetics researchers will need to repeat polygenic risk studies with data from these populations if these predictions are truly going to be useful and equitable.

And yet one more: We shouldn’t take it for granted that intervening with early medication or lifestyle changes for the people at highest risk will make a difference in lowering their risk. Other studies have found that people with higher genetic risk scores for atherosclerosis tend to receive a stronger benefit from statins. But the question needs further testing.

All that said, Yeh, the research cardiologist, says there’s still a lot of optimism around these scores. Current risk factors for heart disease, like high blood pressure or family history, don’t always help single out who truly is most at risk.

“The majority of being who develop coronary artery disease are not people who have a multitude of cardiac risk factors,” Yeh says. “About half of people have just one risk factor, high blood pressure alone. People like that, although they only have one cardiac risk factor, sometimes none, they wouldn’t think of themselves of [having] a very high elevated risk for coronary artery disease.”

A genetic risk factor could help narrow it down.

We’re going to start seeing more and more polygenic tests for disease risk
Polygenic risk scores, says Eric Topol, a cardiologist and geneticist with Scripps Research, “are going to take hold in common medical practice. It’s a matter of when, not if.”

And they’ll be used for conditions outside of heart disease. Indeed, in the latest Nature Genetics study, the researchers also calculated risk scores for diabetes, atrial fibrillation (irregular heart rhythm), inflammatory bowel disease, and breast cancer. The genetic tests for these conditions found fewer people at elevated risk than the tests for heart disease. And not every test will be equally predictive.

Kathiresan points out that while only 8 percent of the study participants were singled out for elevated risk for coronary artery disease, about 20 percent of all the participants were flagged as having elevated risk for at least one of the diseases listed above.

And while these scores are now being generated for all kinds of health and behavioral issues, medicine isn’t really ready to implement them. Huge questions remain. For instance, while it’s possible to do a genetic risk assessment of an infant, or even an embryo, does it make sense or is it even ethical for new parents to learn their embryos or newborns are at a threefold risk for heart disease?

Doctors will also have to think long and hard about how they discuss these kinds of risks with their patients. Scoring in the 70th percentile of risk for coronary artery disease may sound scary, but it won’t increase a person’s chances of getting that disease by all that much.

There are also likely to be unintended consequences of giving patients a new health metric to fear. Consider what happened with cholesterol, a risk factor for heart disease that people began being commonly tested for in the 1980s. Fear of cholesterol came to inspire low-fat food trends. Those dietary trends made food companies money, but they didn’t necessarily make people healthier, especially as many of the foods marketed as low-fat were still loaded with sugar.

What happens when some huckster starts selling vitamins to complement a polygenic risk score, or some other forms of woo? (Currently, you can buy a customized diet guide based on a sequencing of your DNA.) There’s a lot of education that needs to happen here to prevent genetic risk prediction from becoming genetic astrology.

For now, aside from a polygenic risk score for breast cancer, these tests don’t yet exist in the clinic. But they’re going to get easier and easier to discover on your own. If you have your genetics data from a commercial company like 23andMe, you can upload it to a number of sites on the internet to see your risk scores for a slew of traits and diseases. Kathiresan’s team is hoping to build a free tool for people to assess their coronary artery disease risk in this manner.

Here’s a reasonable fear: It’s going to be hard for consumers, without much input from doctors, to know when the risk scores matter and when they do not. Heck, you can currently take a genetics test for intelligence that really won’t tell you anything valuable. It’s possible to develop polygenic risk score for loneliness, baldness, marital status, or really any human trait that is even vaguely influenced by genes. It takes more information — like odds ratios — to know whether those scores really matter in your life.

It will also be hard to know what to do to diminish risk. A high polygenic score for breast cancer might mean a woman wants to make more frequent mammogram appointments, Janssens says. But the current recommendations for people at higher risk of heart disease are things everyone should be doing: living a healthy lifestyle free of tobacco.

“I actually think there’s going to be a whole [medical] field that emerges, kind of like radiology emerged in 1900 with the invention of X-rays,” Kathiresan says, “where [doctors] are basically interpreting that genetic information for medical risk.”

That field needs to start up soon, because there’s a lot more coming.

https://www.vox.com/science-and-health/2018/8/24/17759772/genetics-polygenic-risk-heart-disease-nature

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by Matthew Herper

A Harvard scientist thinks he’s reached a new milestone: a genetic test that helps identify people who are at high risk of having a heart attack. Can he convince doctors to use it?

“I think–in a few years, I think everybody will know this number, similar to the way we know our cholesterol right now,” muses Sekar Kathiresan, director of the Cardiovascular Disease Initiative at the Broad institute and a professor at Harvard Medical School.

Not everyone else is so sure. “I think it’s a brilliant approach,” says Harlan Krumholz, the Harold H. Hines Jr. professor of cardiology at Yale University and one of Kathiresan’s collaborators. But he worries about whether Kathiresan’s tests are ready to compete with the plethora of diagnostic tests, from AI-boosted CT scans to new types of “bad” cholesterol proteins, that are on offer. And he worries about cost. There is no commercial version of the gene test. But the very idea that such a test is not only available, but also near, is the result of a cresting wave of new genetic science, the result of large efforts to gather genetic information from millions of volunteers.

The number in question is what is called a polygenic risk score. Instead of looking for one miswritten gene that causes heart attacks, or, for that matter, other health problems, geneticists are increasingly looking at thousands of genetic alterations without even being sure what each does. In the case of Kathiresan’s polygenic score, the test looks for 6.6 million single-letter genetic changes that are more prevalent in people who have had early heart attacks.

Our genetic inheritances, the current thinking goes, are not so much a set of declarative orders as a cacophony of noise. There are big genetic changes that can have a big effect, but most diseases are the result of lots of tiny changes that add up. In Kathiresan’s words, it’s mostly a gemish (Yiddish for “a mixture”). And it’s not clear which changes are biologically important – Kathiresan says only 6,000 or so of the 6.6 million genetic changes are probably actually causing heart attacks. But finding those specific changes will take a long time. The risk score could be used now.

The effect of this genetic cacophony can be huge. The most common single mutation that increases the risk of heart disease is a gene that causes a disease called heterozygous familial hypercholesterolemia (literally: inherited high cholesterol) that occurs in one person in 250 and triple’s a person’s risk of having a heart attack. But today, in a paper in Nature Genetics, Kathiresan and his colleagues present data that 5% to 8% have a polygenic score that also at least triples their risk of having a heart attack. That’s about 20 times as many people, Kathiresan says.

“These patients are currently unaware of their risk because the polygenic patients don’t have higher levels of the usual risk factors,” Kathiresan says. “Their cholesterol is not high. Their blood pressure is not that high. They are hidden from the current risk assessment tools.”

In the Nature Genetics paper, Kathiresan’s team tested the 6-million-variant polygenic score in two groups of patients numbering, respectively, 120,280 and 288,978 people, from the U.K. BioBank, a government-backed effort in the United Kingdom to collect genetic data. For some patients, the risk was even higher, with the genetic changes predicting a fivefold increase in heart attack risk. The paper also argues that polygenic risk scores could be used to predict risk of conditions such as type 2 diabetes and breast cancer.

Another study, yet to be published, looked at the prevalence of both familial hypercholesterolemia and the polygenic score in a population of people who had heart attacks in their 40s and 50s, Katherisan says. Only 2% had familial hypercholesterolemia, but 20% had a high polygenic risk score. Knowing one’s polygenic risk score might matter. A 2016 paper in the New England Journal of Medicine showed that people with high polygenic scores had fewer heart attacks if they had healthier lifestyles, and a 2017 paper in the medical journal Circulation showed that patients with high polygenic risk scores got an outsize benefit from cholesterol-lowering statin drugs. Those papers, both by Kathiresan’s group, used a score that included only a few dozen gene variants.

Doctors should be skeptical of such a test. There’s a long history of tests in medicine that have done more harm than good by leading to people to take drugs they do not need. Cardiologists have gotten used to even higher standards for data. For instance, many might want to see if the test can show a benefit in a large study in which people are tested at random. Many will want more evidence that the test can identify people at high risk they’d otherwise miss, as Kathiresan says, and that it doesn’t lead to treatment in those who don’t need it. Kathiresan says he hopes to do a study in the highest-risk individuals to prove that statin drugs can lower their risk. If the test becomes a commercial prospect, more studies will drive up the eventual cost.

Kathiresan is hoping to follow a less expensive path. He notes that 17 million people have already used genotyping services like 23andMe and Ancestry. He hopes that people who use those services (23andMe costs $99, Ancestry $59) will submit their data to a portal he’ll build for free. He also says he’s in discussions with commercial providers, but he’s hoping that people will be able to get their polygenic scores for about as much as the cost of a cholesterol test. For the people at the highest risk, he argues, this is information that could be important. For others, he argues, why deny people information that has been scientifically validated?

Whether Kathiresan can really pull off a low-cost version in a medical system that is optimized to make money is as big a question as whether the test is ready for prime time. Krumholz worried about the cost of the test until a reporter told him of Kathiresan’s planned website. “If you say it’s free, I’m going, ‘Why not?'” Krumholz says. “It’s a better family history,” he says, comparing the test to asking whether a relative has had a heart attack. But that may be the biggest ‘if’. If anything is more puzzling than genetics, it is the economics of healthcare in the U.S.A.
https://www.forbes.com/sites/matthewherper/2018/08/13/a-harvard-scientist-thinks-he-has-a-gene-test-for-heart-attack-risk-he-wants-to-give-it-away-free/#557490e85959

By Sarah C. P. Williams

There’s a reason people say “Calm down or you’re going to have a heart attack.” Chronic stress—such as that brought on by job, money, or relationship troubles—is suspected to increase the risk of a heart attack. Now, researchers studying harried medical residents and harassed rodents have offered an explanation for how, at a physiological level, long-term stress can endanger the cardiovascular system. It revolves around immune cells that circulate in the blood, they propose.

The new finding is “surprising,” says physician and atherosclerosis researcher Alan Tall of Columbia University, who was not involved in the new study. “The idea has been out there that chronic psychosocial stress is associated with increased cardiovascular disease in humans, but what’s been lacking is a mechanism,” he notes.

Epidemiological studies have shown that people who face many stressors—from those who survive natural disasters to those who work long hours—are more likely to develop atherosclerosis, the accumulation of fatty plaques inside blood vessels. In addition to fats and cholesterols, the plaques contain monocytes and neutrophils, immune cells that cause inflammation in the walls of blood vessels. And when the plaques break loose from the walls where they’re lodged, they can cause more extreme blockages elsewhere—leading to a stroke or heart attack.

Studying the effect of stressful intensive care unit (ICU) shifts on medical residents, biologist Matthias Nahrendorf of Harvard Medical School in Boston recently found that blood samples taken when the doctors were most stressed out had the highest levels of neutrophils and monocytes. To probe whether these white blood cells, or leukocytes, are the missing link between stress and atherosclerosis, he and his colleagues turned to experiments on mice.

Nahrendorf’s team exposed mice for up to 6 weeks to stressful situations, including tilting their cages, rapidly alternating light with darkness, or regularly switching the mice between isolation and crowded quarters. Compared with control mice, the stressed mice—like stressed doctors—had increased levels of neutrophils and monocytes in their blood.

The researchers then homed in on an explanation for the higher levels of immune cells. They already knew that chronic stress increases blood concentrations of the hormone noradrenaline; noradrenaline, Nahrendorf discovered, binds to a cell surface receptor protein called β3 on stem cells in the bone marrow. In turn, the chemical environment of the bone marrow changes and there’s an increase in the activity of the white blood cells produced by the stem cells.

“It makes sense that stress wakes up these immune cells because an enlarged production of leukocytes prepares you for danger, such as in a fight, where you might be injured,” Nahrendorf says. “But chronic stress is a different story—there’s no wound to heal and no infection.”

In mice living with chronic stress, Nahrendorf’s team reported today in Nature Medicine, atherosclerotic plaques more closely resemble plaques known to be most at risk of rupturing and causing a heart attack or stroke. When the scientists blocked the β3 receptor, though, stressed mice not only had fewer of these dangerous plaques, but also had reduced levels of the active immune cells in their plaques, pinpointing β3 as a key link between stress and atheroscelerosis.

The finding could lead to new drugs to help prevent cardiovascular disease, suggests biologist Lynn Hedrick of the La Jolla Institute for Allergy and Immunology in San Diego, California. “I think this gives us a really direct hint that the β3 receptor is important in regulating the stress-induced response by the bone marrow,” Hedrick says. “If we can develop a drug that targets the receptor, this may be very clinically relevant.”

More immediately, the new observations suggest a way that clinicians could screen patients for their risk of atherosclerosis, heart attack, and stroke, Tall says. “Rather than asking four questions about stress levels, we could use their white blood cell counts to monitor psychosocial stress,” he says.

Thanks to Dr. Rajadhyaksha for bringing this to the attention of the It’s Interesting community.

http://news.sciencemag.org/biology/2014/06/how-stress-can-clog-your-arteries