One of the new CF drugs, VX-770, was designed to tackle a much rarer CF-causing mutation. Called G551D, it’s behind about 4% of U.S. cases; the protein gets to the cell surface like it’s supposed to, but it’s closed up tight and can’t function. VX-770, designed by Vertex Pharmaceuticals, opens the protein into the right configuration so it can do its job. VX-770 was approved in 2012 for patients with this particular mutation, under the brand name Kalydeco.