We're not even at the point where we're allowed to get all up in people's stem cells to help cure diseases, but researchers are already thinking ahead to how we can use stem cells to treat genetic diseases, which should be impossible. Or, it was impossible, until we just did it.
A stem cell is a type of cell that can turn into just about any other kind of cell in the body. They're a stupendously valuable medical tool because if you have, say, an [insert almost anything here] that is damaged or dysfunctional, you can just send some stem cells in to go take over, and they'll turn into new copies of whatever you need. Of course, it's immensely more complicated than that in practice, but there's a huge amount of potential there, and we've already had a substantial amount of success curing mice of things like diabetes.
The tricky bit about using stem cells to treat a disease caused by a genetic mutation is that when you get the stem cells from your patient, they'll all have that same genetic mutation, and you're back to square one. You can try getting stem cells from someone else, but then you run into all kinds of rejection problems. Researchers at the Wellcome Trust Sanger Institute and the University of Cambridge have managed to harvest stem cells from a patient with a genetic mutation, fix that mutation, and then use those repaired cells to successfully treat the disease that the mutation was causing in the first place.
The mutation in question is a change to one tiny little piece of DNA that results in cirrhotic liver disease, which generally requires a liver transplant for effective treatment. Instead, researchers were able to take skin cells from a patient with the disease and turn them directly into stem cells. These stem cells still had the mutation, of course, but by using an engineered enzyme to snip out the mutated area and then replace it with a piece of normal DNA, effectively "repairing" the genome itself. The fixed-up stem cells were turned into liver cells and implanted into mice, and they worked perfectly, without any signs of disease.
There are two reasons that we're not all benefiting from these techniques right now. One is safety: genes that have been artificially altered tend to have a propensity towards cancer, but the hope is that by just changing the one little mutated bit and nothing else, cancer won't be a factor. That said, it's going to take a lot more research to prove that this sort of therapy is safe for humans. The other reason is that right now, doing this kind of thing on an individual level is absurdly expensive. But this is the case with just about everything when it's first invented, and the potential for medicine like this is just so enormous that we can only hope it'll become standard, affordable practice soon enough that we can all benefit from it.