Researchers have developed a way to edit the genetic sequences at the root of Huntington’s disease and Friedreich’s ataxia. If longer than a certain threshold length, these sequences grow in length uncontrollably and lead to brain cell death in Huntington’s disease, and the breakdown of nerve fibers in Friedreich’s ataxia. There are no treatments that stop the progression of these diseases. Using base editing, the team introduced single-letter changes into the middle of the repeated stretch of DNA, interrupting the sequence in patient cells and mouse models of Huntington’s disease and Friedreich’s ataxia. They found that the edited DNA tracts stayed the same in length or even became shorter over time.