Additional Study Information: The purpose of this study is to find out if you can take the prescribed dose of VX-371 without problems, and whether VX-371 is safe and helps subjects with PCD. VX-371 is called an investigational or experimental drug because it has not been approved for use in people by the Food and Drug Administration (FDA), the branch of U.S. government which approves new drugs, or by any other regulatory agency in other countries. Inhaled HS is sometimes used to treat PCD patients. HS is extra-salty water that is sterile, so there are no germs in it. HS is also considered experimental in this study.