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Shares of diagnostic test maker Myriad Genetics Inc. fell Thursday after the Supreme Court issued a mixed ruling in a case involving the company's patents on genes at the center of its proprietary tests for increased risk of breast and ovarian cancer.

Myriad's shares on the Nasdaq stock exchange were up most of the day, including more than 10 percent at one point, but fell into negative territory in the final hour of trading. The share price plunged as much as 10 percent but recovered enough to finish the day at $32.01, down 5.63 percent.

Myriad, based in Salt Lake City, sells a test for a specific gene linked to breast cancer — the only test had been available for those genes. They were challenged, leading to the Supreme Court's review, even though the U.S. Patent and Trademark Office has been awarding patents on human genes for almost 30 years.

The high court ruled that genes naturally found in the body cannot be patented, but that synthetically created genetic material, called cDNA, can be patented. That leaves an opening for Myriad to continue making money, Justice Clarence Thomas wrote in the court's majority decision.

Patents give inventors the right to prevent others from making, using or selling a novel device, process or application, usually for a number of years.