WASHINGTON — The Supreme Court ruled Thursday that companies cannot patent parts of naturally-occurring human genes, a decision with the potential to profoundly affect the emerging and lucrative medical and biotechnology industries.

The high court's unanimous judgment reverses three decades of patent awards by government officials. It throws out patents held by Salt Lake City-based Myriad Genetics Inc. on an increasingly popular breast cancer test brought into the public eye recently by actress Angelina Jolie's revelation that she had a double mastectomy because of one of the genes involved in this case.

Justice Clarence Thomas, who wrote the court's decision, said that Myriad's assertion — that the DNA it isolated from the body for its proprietary breast and ovarian cancer tests were patentable — had to be dismissed because it violates patent rules. The court has said that laws of nature, natural phenomena and abstract ideas are not patentable.