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Hemophilia is a devastating genetic condition—without the ability to form blood clots, those who have it risk bleeding to death from even the slightest cut.

But scientists at the University of Pennsylvania have their sights set on a potential cure. Working in mice, they used the gene editing technique CRISPR to repair defective genes in a clotting protein called factor IX, the source of the mutations that cause hemophilia B. And it worked.

“Basically we cured the mice,” Dr. Lili Wang, the lead author on a forthcoming paper presented Monday at the Annual American Society of Hematology Meeting, told me. “With a gene therapy like this, hopefully we can just people one injection and correct them forever.”

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Hemophilia is a single-gene disease, caused by different mutations scattered within a specific gene for the clotting protein factor IX. Those mutations can vary from person-to-person, so the researchers needed to develop an approach that could target different mutations. Working with mice that had been modified to knock out the clotting protein completely, scientists used human DNA and CRISPR to design a genetic therapy that would stimulate the production of the clotting protein in the mouse’s liver. Over a period of four months, injections into more than a dozen newborn and adult mice saw a return of clotting protein levels to normal. To test the success of the experiment, some of the mice underwent a partial liver transplant.

“Normally, a hemophiliac mouse would die during a surgery,” Wang said. All of the mice survived.

The technique, she told me, could potentially work on most patients with hemophilia B, the most common form of hemophilia. In theory, it would last years or even a lifetime—much longer than the arduous continual treatment most patients continually undergo. This is good news for the 20,000 people in the U.S. living with some form of hemophilia.

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Before you get too excited, it’s important to note that this research is still in the very early stages. Before even thinking about taking her breakthrough to human trials, Wang will need to replicate the results in a larger mouse trial, and likely also in a larger mammal. We are, in other words, still a long way from using CRISPR to rid the world of hemophilia.

The most exciting breakthrough here, though, may not have to do with hemophilia at all.

Her strategy may translate to other genetic conditions rooted in the liver, and potentially other organs, too.

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“This shows that in vivo genome editing can cure disease,” Wang said.