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It’s common to think of cancer as a disease driven by the buildup of mutations in the DNA of cells. Everything from pollutants to cigarettes to exposure to everyday chemicals can alter genes, and continued exposure over a lifetime can lead to a critical mass of mutations.
Now, researchers say the same process may be at work in heart disease. In a paper published in the New England Journal of Medicine, Dr. Sekar Kathiresan, from the Broad Institute of Harvard and MIT, and Dr. Benjamin Ebert from Brigham and Women’s Hospital and their colleagues found a gene that builds up mutations over a lifetime and can double the risk of heart events.
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While there are genes associated with greater heart disease risk, most of them are inherited. The new mutations linked to heart problems are among the first to be acquired, or picked up over a lifetime. The mutations develop among a group of blood cells known as stem cells, which divide throughout a person's lifetime to replenish the supply of blood cells. The genetic changes the researchers found are also linked to a higher risk of developing blood cancer, but they seem to have a stronger effect on heart disease than cancer.
“This is a totally different type of risk factor than hypertension or hypercholestserolemia [high blood cholesterol] or smoking,” says Kathiresan. “And since it’s a totally different risk factor that works through a different mechanism, it may lead to new treatment opportunities very different from the ones we have for heart disease at present.”
Kathiresan and his team actually found the gene several years ago when they linked it to a 10-fold higher risk of developing blood cancers. Although the mutations increased cancer risk, the cancers were still relatively rare, but people who had them had a 40% higher risk of dying of other causes. Among those was heart disease. In the new paper, the researchers looked at four different populations of nearly 8,000 people who had their genomes sequenced. Even among younger people, those with the mutations—called clonal hematopoiesis of indeterminate potential, or CHIP—showed a higher rate of heart disease.
“We were fully expecting not to find anything here,” says Kathiresan. “But the odds of having an early heart attack are four-fold higher among younger people with CHIP mutations.”
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What’s significant about the CHIP mutations are that they aren’t inherited. They are accumulated over time, from exposures to all sorts of things that can damage DNA. Among people over 70, 10% of people have these mutations, says Kathiresan. Whether they develop heart problems (or cancer) depends on how many of the mutated cells are circulating in the blood. “The load of mutations increases over time," Kathiresan says. "The higher the load, the more the risk of heart disease.”
Fortunately, there are ways to detect the mutated cells. Currently available blood tests for blood cancers can easily keep track of the volume of mutated cells, which means that monitoring the CHIP mutations could be a new way to identify people at higher risk of having heart problems, keep track of their risk and guide treatments.
When the researchers introduced the CHIP mutations into mice, they learned more about how a cancer-causing gene can contribute to heart disease. It appears that the CHIP mutations cause atherosclerotic plaques in the blood vessels, which contributes inflammation and hardening of the arteries that can trigger heart attacks.
There's still a lot to learn. As exciting as the findings are, it’s still too early to add CHIP testing to routine blood screening to identify people at higher risk of having heart problems. And because CHIP contributes to heart disease in a new way, it’s possible that the mechanisms to control CHIP-related heart events have nothing to do with cholesterol, exercise and blood pressure. “The mouse work suggests that the path to heart disease is something different from what we have been working on so far,” says Kathiresan.
More work needs to be done to determine if there are ways to counteract the effect of the mutation on plaques or control the rate at which the mutations build up in these cells. “Currently there isn’t a drug that’s safe enough or efficacious enough to treat people with,” says Ebert. “But it’s a very active area of research to identify interventions that can decrease the size of the mutated cell population or potentially eliminate them.”