A subsidiary of Amgen Inc. has discovered a rare variation in the sequence of a human gene that gives people a significant reduction in levels of “bad” cholesterol and lowers the risk of heart attacks, the company announced Wednesday. DeCODE Genetics in Reykjavik, Iceland, a wholly owned subsidiary of Amgen, the biotech in Thousand Oaks, used population and genetic data in Iceland to isolate the rare gene variation. Researchers linked the variation to a 35 percent reduction in the risk of coronary artery disease and heart attack. Also, the variation “confers greater protection against coronary heart disease than can easily be accounted for by the reduction in cholesterol alone,” the company said. The variation involves missing molecules in the sequence of the gene, and Amgen is working on a drug to block those sections in patients who don’t have the variation. Dr. Kari Stefansson, chief executive at DeCODE, said the discovery has direct application to improving the health of people around the world, and is part of Amgen’s ongoing research program on the genetic basis of disease. Amgen shares closed up 72 cents or less than a percent to $150.83 on the Nasdaq.