This year's Nobel Prize in Physiology or Medicine goes to two American researchers, Andrew Fire of Stanford University and Craig Mello of the University of Massachusetts. They won for discovering how to selectively silence genes that are causing disease. Fire and Mello will share the $1.4 million prize.

Joining me now is NPR's Richard Knox. Richard, this is a complicated discovery, can you just walk us through what the researchers did?

RICHARD KNOX: Basically, it's called RNA interference - that's what they discovered - and it's a way for cells to turn off genes one at a time. To go back to high school biology, genes are made of DNA and each gene contains the instructions to make a particular protein. Proteins do all the work of living cells.

To make a protein, a DNA gene has to get translated into RNA. And normally RNA occurs as a single strand of molecules, like, you know, pearls on a necklace. But certain viruses have two strands of RNA, and sometimes little stretches of RNA in normal cells get duplicated into a double strand. Either way, it spells trouble. So cells crank up this RNA interference program which blocks the process; in effect, it silences the gene. That's a good thing if you're trying to stop a virus in its tracks. It's also a good thing if you're trying to block a bad protein, like, say, one that's involved in Alzheimer's disease or diabetes.

AMOS: So tell us the bigger picture here. Why is this switch important?

KNOX: This is one of those discoveries that seems to have really broad application. You know, from really basic science questions, like how do we age, to applied stuff in medicine, such as how can we reverse high cholesterol. The key thing is that RNA interference allows scientists to turn off specific genes, and that's really a tremendously useful tool for researchers who want to understand how genes control things, like embryonic development or aging. And scientists think RNA interference will also help devise new medicines against a wide variety of diseases - heart disease and cancer and viral infections like HIV and hormone disorders. You know, it's a long list.

AMOS: Wow. Researchers have it as a tool, but what about doctors? Can you use this to treat patients yet?

KNOX: That's just beginning. The first human studies of an RNA interference drug involves people with an eye disease called macular degeneration. These people have an overgrowth of blood vessels in the eye and the drug is deigned to block the faulty genes that cause that, or gene that causes that.

There are other drugs in the pipeline. Recently, researchers showed that they could use RNA interference to lower bad cholesterol in mice. A lot of drug companies are investing in this kind of research because it offers a whole new way, and a very selective way, to make drugs against basic disease mechanisms.

AMOS: Thanks. NPR's Richard Knox.

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