The widely used process has helped scientists use mice to study heart disease, diabetes, cancer, cystic fibrosis and other diseases.

The prize is shared by Mario R Capecchi, 70, of the University of Utah in Salt Lake City; Oliver Smithies, 82, a native of Britain now at University of North Carolina in Chapel Hill, and Sir Martin J Evans, 66, of Cardiff University in Wales.

The Nobel is a particularly striking achievement for Capecchi. A native of Italy, he was separated from his mother at age 4 when she was taken to the Dachau concentration camp as a political prisoner during World War II.

For four years, Capecchi lived on the street or in orphanages, “and most of the time hungry,” he recalled in a University of Utah publication in 1997. Malnutrition sent him to a hospital where his mother found him on his ninth birthday. Within two weeks they left for the United States, where he went to school for the first time, starting in third grade despite not knowing English.

In a telephone interview from Salt Lake City, Capecchi called the award “a fantastic surprise.”

The three scientists were honoured for a technique called gene targetting, which lets scientists inactivate or modify particular genes in mice. That in turn lets them study how those genes affect health and disease.

“Gene targeting has pervaded all fields of biomedicine. Its impact on the understanding of gene function and its benefits to mankind will continue to increase over many years to come,” said the citation for the $1.54 million prize.

Steve Brown, director of the mammalian genetics unit at the Medical Research Council in London, said the three researchers have “given us the toolkit to understand how genes function” in mice and so, by extension, in humans. As a result, of their work, he said, “we’re on the cusp of having a much better understanding of the relationship between genes and disease.”

Evans said, “I haven’t come to terms with it yet. In many ways it is the boyhood aspiration of science, isn’t it? And here I am unexpectedly with it. It’s amazing.”

Smithies told The Associated Press getting award was “very gratifying.” After working on the research for more than 20 years, he said it’s “rather enjoyable being recognised at this level.” Smithies said he hopes winning the prize will make it easier to secure funding for other work.