In a lively Supreme Court argument on Monday, the justices struggled to find a narrow way to rule on the momentous question of whether human genes may be patented.

“Why should we jump in and decide the broadest possible question?” asked Justice Samuel A. Alito Jr.

Some justices expressed concern about making sure that businesses continue to engage in expensive research. Others worried that allowing genes to be patented would shut down innovation. Justice Sonia Sotomayor suggested that an isolated gene is “just nature sitting there.”

The court’s ruling in the case will shape the course of scientific research and medical testing, and it will affect the willingness of businesses to invest in the expensive work of isolating and understanding genetic material.

The case concerns patents held by Myriad Genetics, a Utah company, on genes that correlate with increased risk of hereditary breast and ovarian cancer. The decision in the case could affect not only thousands of patented genes but also pharmaceuticals, vaccines and genetically modified crops.

The central question for the justices in the case was whether isolated genes are ‘products of nature’ that may not be patented or ‘human-made inventions’ eligible for patent protection.

The patents were challenged by scientists and doctors who said that their research and ability to help patients had been frustrated. Christopher A. Hansen, a lawyer for Ostrer with the American Civil Liberties Union, said Myriad deserves credit for its work but not a patent.

“What exactly did Myriad invent?” Hansen asked. “The answer is, nothing.”

A lawyer for the company, Gregory A. Castanias, said the genes do not occur in nature and were, isolated thanks to human ingenuity.

In a unanimous decision last year, the Supreme Court said that medical tests relying on correlations between drug dosages and treatment are not eligible for patent protection. Natural laws, Breyer wrote for the court, may not be patented standing alone or in connection with processes that involve “well-understood, routine, conventional activity.”

Solicitor General Donald B. Verrilli Jr., representing the federal government said: “merely isolating a gene was not sufficient for patent protection. Manipulating a gene to create something not found in nature would be.” — New York Times News Service