(CNN) -- Here's a little-known fact: Under current law, it's possible to hold a patent on a piece of human DNA, otherwise known as a gene.

Some breast cancers, shown here, are linked with the genes BRCA1 and BRCA2.

Companies that have acquired patents for genes have specific rights to their use, which may include diagnostic tests based on those genes, as well as future mutations that are discovered.

In a new lawsuit, the American Civil Liberties Union alleges that the policy is unconstitutional.

The targets of the lawsuit, Myriad Genetics and the University of Utah Research Foundation, hold patents to BRCA1 and BRCA2, the genes responsible for many cases of hereditary breast and ovarian cancers.

The U.S. Patent and Trademark Office is also named in the suit.

The lawsuit asserts that the patents prevent some people from accessing medical screening for BRCA1 and BRCA2. It also challenges the general patentability of genes, which has been legal since 1980. That year, in Diamond v. Chakrabarty, the Supreme Court found in favor of Ananda Mohan Chakrabarty, who used bacteria to engineer a microbe that dissolves oil. Watch Dr. Gupta explain the lawsuit »

Genes form the basic unit of heredity. With modern technology, researchers have determined that particular genes carry an associated risk of illness.

A striking 20 percent of all human genes have been patented. However, now that all 20,000 to 25,000 human genes have been mapped and sequenced through the Human Genome Project, they are in the public domain, meaning they would no longer be considered "new" for the purposes of patents, said Lee Silver, professor of molecular biology and public policy at Princeton University. Now, patents on human genes must specify a new use, such as a diagnostic test.

If a company wants to patent the purified form of an antibiotic that exists in nature in a fungus, no one challenges that, Silver said. Plant DNA, as well as human DNA, can be synthesized in a laboratory. Distinguishing this case from a patented human gene that is useful in diagnostics would require the ethical argument that the human genome is sacred -- and even then, things get murky, considering that about 25 percent of human genes are shared by chimpanzees, he said.

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"The patent law says nothing about ethics," he said.

But Josephine Johnston, bioethicist at the nonpartisan Hastings Institute, said she thinks that allowing patents for human genes was probably a mistake. She said she would draw the line at modified genes being acceptable as intellectual property, but not genes in pure form. From a legal point of view, that would mean unmodified plant and animal genes would also be off-limits.

In a moral argument, however, one could say that there is a "common humanity" -- that human genetic material belongs to all humans -- or agree that no plant or animal genes should be patented.

"I think that legal arguments about why this kind of thing isn't really something that should be patentable are really strong at a theoretical level," she said. "I wouldn't be that confident that the American court system would agree."

Patents protect inventors and spur innovation by giving companies an incentive to create new things. The invention must be "useful," "novel" and "nonobvious" and carry a description that enables someone to use it for the stated purpose, according to U.S. patent law.

Dan Ravicher, executive director of the Public Patent Foundation, who partnered with the ACLU in the lawsuit, said the lawsuit's argument is akin to "saying if someone removes your eyeball ... just because you remove the eyeball and wash it off, that doesn't make the eyeball patentable."

But Silver finds this analogy faulty. Though an individual's eyeball is unique and cannot be made in a laboratory, any given form of any gene is present in many people and can be synthesized. The DNA molecule is defined at the atomic level by a genetic sequence. Scientists can make purefied substances with the same characteristics as human genes, whereas they cannot exactly manufacture any person's eyeball.

"The main problem is that people don't understand what genes are and what they're not," Silver said.

Some ethicists do not take issue with Myriad's patents but with how the company uses them. Part of the ALCU's argument is that Myriad charges $3,000 for its diagnostic cancer test, a price that prevents some women from seeking this preventive measure.

"I think we're talking about unreasonable profit and exploitation of people at risk," said M. Sara Rosenthal, director of the University of Kentucky Program for Bioethics. "The issue is greed, which is never ethical."

From Rosenthal's perspective, the main issue in this case is no different from a situation in which a pharmaceutical company, regardless of where the ingredients came from, uses a patent to charge unreasonably high prices for drugs. Such companies have a right to recoup their costs, but they should make their health care products available to the average person, she said.

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The patentability of such tests, however, gives companies an incentive to create them in the first place, Silver said.

"If you patent any diagnostic test, this should be no different," he said.

Myriad's attorney, Richard Marsh, said Wednesday that the company plans to "vigorously defend our intellectual property rights."

The patents on genes also expire 20 years after the date of application, meaning the plethora of existing patents on the human genes themselves will run out relatively quickly, Silver said. Moreover, with exceptions such as BRCA1 and BRCA2, there are relatively few genes whose patentability is actually profitable, Silver said.

"I suspect that 95 percent of patents on genes are worthless in an economic sense," he said.

A good use of a gene patent was for the insulin gene, which led to recombinant human insulin, which led to essential treatments for diabetes, Rosenthal said.

"Gene patenting should not mean that commercial companies unreasonably profit from those of us unlucky in genetic lotteries," she said.

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