Gene therapy rises from the dead

Gene therapy--the idea of replacing a patient's defective genes with healthy ones--was hyped in the 1990s as the next big leap forward in drug development. But a series of high-profile setbacks left the entire gene therapy field on death's doorstep. Yet today, 189 companies are developing gene therapies, and 354 U.S. studies are being conducted as developers continue to pursue game-changing treatments for some of the most difficult-to-treat diseases. Gene therapy was first used to treat a...