Breakthrough method means CRISPR just got a lot more relevant to human health

The gene-editing tool CRISPR may one day change the way humans approach medicine — or at least that’s how it’s been portrayed so far. But for all the talk of using CRISPR to eliminate disease, the method was never very good at doing one important thing: altering single letters of DNA. (DNA is made of four chemical units, represented by the letters A, T, G, and C.) Now, scientists at Harvard University say they've modified the CRISPR method so it can be used to effectively reverse mutations involving changes in one letter of the genetic code. That’s important because two-thirds of genetic illness in humans involve mutations where there’s a change in a single letter.