The biggest prize in medical science has been won by two scientists who have pioneered a genetic technique that promises to revolutionise medicine in the 21st century.
This year's Nobel Prize for Medicine has been awarded for the discovery of RNA interference (RNAi) - a naturally occurring process for switching off specific genes.
Scientists are already using the technique routinely as a highly effective research tool, but the wider interest comes from RNAi's potential medical applications. Specialists believe RNAi could be used to develop radical new treatments for a variety of incurable disorders from Huntington's disease and certain forms of blindness to heart disease, diabetes and cancer.
Andrew Fire, 47, of Stanford University in California, and Craig Mello, 45, of the University of Massachusetts Medical School, were told yesterday that they would share the £800,000 prize money for identifying and naming RNAi in a scientific paper published in the journal Nature in 1998.
Professor Mello said yesterday that they were both still relatively young for receiving a Nobel Prize, which came sooner than expected given that many previous Nobel laureates have had to wait decades for recognition. "I knew it was a possibility, but I didn't really expect it for perhaps a few more years. Both Andrew and I are fairly young, 40 or so, and it's only been about eight years since the discovery," Professor Mello said.
Professor Fire, who worked at the Carnegie Institution in Washington when the research was carried out, said that the breakthrough would not have happened without other people's involvement. "Science is a group effort. Please recognise that the recent progress in the field of RNA-based gene silencing has involved original scientific inquiry from research groups around the world," he said.
The original observations that led to the discovery go back to 1990, when Richard Jorgensen of the University of Arizona in Tucson noticed that he could turn purple petunia flowers white by injecting them with a gene for pigment coloration.
Professor Jorgensen called the process "co-suppression", but the mechanism remained elusive until Professors Fire and Mello carried out their own studies in the laboratory using a microscopic nematode worm. They found they could switch off or "silence" particular genes in the worm by injecting it with double-stranded fragments of a molecule called RNA - which closely resembles the DNA blueprint of life.
The Nobel Assembly at the Karolinska Institute in Stockholm said: "Although it was evident RNA played a key role in gene silencing, the phenomenon remained enigmatic until the discovery of RNA interference provided a most unexpected explanation with many profound consequences. It was evident from the very beginning that the significance of the discovery of RNAi would be exceptional."
Further work has shown that RNAi appears to be a ubiquitous process in living organisms. In 2002, scientists demonstrated that it also works in human cells. This led to speculation that it might be possible to turn off diseased genes that cause cancer or inherited disorders such as Huntington's, or that RNAi could be adapted to sabotage the vital genes of viruses such as HIV.
Professor Chris Higgins, director of the Medical Research Council's Clinical Sciences Centre in London, said that the discovery of RNAi has revolutionised the understanding of how genes can be controlled. "Perhaps even more importantly, it provides a simple tool for manipulating gene expression in the laboratory, and with great promise for altering gene expression to treat diseases such as viral infections and cancer," Professor Higgins said.
Drug companies such as GlaxoSmithKline and Pfizer have already taken out licenses on various RNAi techniques in the hope of developing new therapies.
* Blindness: Two biotechnology companies, Sirna of Boulder, Colorado, and Acuity, of Philadelphia, are conducting clinical trials involving patients with macular degeneration. RNAi could block the growth of harmful blood vessels in the eye that cause visual impairment.
* Huntington's disease: RNAi is being considered as a way of turning off the gene that causes Huntington's.
* HIV and Aids: Scientists hope to disable the Aids virus by silencing one of the genes it needs for replication.
* Heart disease: If scientists can switch off a gene involved in the build-up of cholesterol in the body they might be able to treat people who are born with very high levels of this damaging fat.
* Cancer: RNAi could be adapted to silence cancer-causing genes. Test-tube studies have proved successful.