Triglycerides are lipids that the body makes from unused calories in food and later burns as fuel. Doctors often monitor patients’ blood levels of these compounds because higher levels have been linked to a greater risk of heart disease.

One player in processing triglycerides is a protein called ApoC-III that is encoded by the gene APOC3. Five years ago, researchers discovered a mutation in APOC3 in 5% of the Amish population in Lancaster County, Pennsylvania. Those with this variant had unusually low levels of triglycerides after consuming a fat-laden milkshake. They also had only half as much ApoC-III protein in their blood, and they were less likely to develop calcification of coronary arteries, which can lead to coronary heart disease.

The Amish group was too small to allow researchers to directly link the genetic mutation to less heart disease, however. And it wasn’t clear whether the gene would show up in non-Amish people.

Now, researchers have found APOC3 mutations in the general U.S. population. They sequenced the protein-coding DNA, or exomes, of 3734 white and African-American volunteers, then combed through the data for genetic variants linked to triglyceride levels. A few people turned out to have either the Amish APOC3 mutation or one of three other variants in APOC3 that also disable this copy of the gene. When the team checked the DNA of a larger group of nearly 111,000 people, they found that about one in 200 carried one of the four APOC3 variants, reported Jacy Crosby of the University of Texas Health Science Center, Houston, who represented a large consortium called the National Heart, Lung, and Blood Institute Exome Sequencing Project.

The 500 or so people with one of these APOC3 variants not only had less ApoC-III in their blood and 38% lower triglyceride levels than the average person; they also had a 40% lower risk of coronary heart disease, whose effects include heart attacks. This result firms up the link between APOC3 and heart disease and also supports a possible prevention strategy, Crosby said: Reducing levels of the ApoC-III protein could potentially lower lipid levels and protect against heart disease. One such drug is already in clinical testing, she noted.

The new study “is exciting, but one has to be cautious” about whether such a drug will work, says geneticist Stephen Rich of the University of Virginia in Charlottesville. That’s because inhibiting ApoC-III late in life may not mimic being born with an APOC3 mutation, which protects for a lifetime, he says.