Researchers at the Broad Institute of Harvard and MIT have developed a new tool that would theoretically make it possible to correct the genetic errors behind about 15,000 of these illnesses—including sickle-cell disease, cystic fibrosis and several forms of congenital deafness and blindness.

The new tool, called ABE (adenine base editors), is more like an editing pencil, according to lead researcher David Liu. It lets scientists precisely change individual pairs of bases—the “letters” that form the “sentences” of the vast human genome—and thus might help address diseases like sickle cell that can be treated with a single letter change.