A new way to make powerful changes at will to the DNA of humans, other animals and plants, much like how a writer changes words in a story, could usher in a transformation in genetic medicine.

Scientists are not just excited about this recently discovered technique because it can snip and edit DNA with precision. It can also do the job more easily and cheaply than other gene-editing methods, making possible research that has historically been difficult, experts say.

Now some of the biologists who unlocked this tool, derived from the immune system of bacteria, are forming companies around it. Although this molecular system, known as Crispr, is not fully understood, researchers believe it can be harnessed to create therapies for intractable genetic diseases.

One of those scientists, UC Berkeley Professor Jennifer Doudna, was part of the team that in 2012 first demonstrated the technique. It is now employed by two companies she has co-founded: Caribou Biosciences in Berkeley, and Editas Medicine in Cambridge, Mass. The latter started last year with $43 million in venture capital. Another company, the aptly named Crispr Therapeutics in Switzerland, has $25 million in the bank, and other biotechnology companies are experimenting with the procedure.

"In principle, this is a technology that could enable correction of genetic mutations that would otherwise lead to disease," said Doudna, a professor of chemistry and biochemistry and molecular biology, in a telephone interview. She was among several experts who spoke at a UC Berkeley conference on the subject last month.

But because the method is in its infancy and has little precedent with the agencies that regulate medicines, it will almost certainly be a long time before a Crispr-based therapy makes it to market.

Its potential risks also concern some bioethicists.

"In the very worst case, technologies that can cause permanent inheritable changes in people bring you very close to the risk of modern eugenics," said Pete Shanks, a consultant who blogs about the topic for the Center for Genetics and Society, a bioethics watchdog organization in Berkeley. "Pretty much everyone agrees that we should avoid that. How we do that, comes the question."

The technique operates on the recent discovery that bacteria, like humans, have an immune system that remembers viruses that have attacked before. To protect themselves, bacteria chop up and incorporate short fragments of foreign invaders' genetic code so they know to destroy a virus should it strike again. It is their equivalent of developing vaccines.

Those new fragments in the bacterial genome add up to an "unusual structure," first reported in the late 1980s by scientists who called them "clustered regularly interspaced short palindromic repeats" - Crispr for short. But Crispr's role, to fight infections, wasn't confirmed until 2007.

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Editing DNA could be genetic medicine breakthrough - SFGate