U.S. health regulators have approved the first gene therapy for hemophilia, a blood-clotting disorder with few treatment options. The maker of the one-time treatment said the drug will cost $3.5 million, making it one of the most expensive drugs ever launched. The Food and Drug Administration approved the drug Tuesday for people with hemophilia B, the less common form of the disease. Other companies are working on similar gene therapies for hemophilia A, which accounts for most cases. Hemophilia almost always strikes males and can cause dangerous, extended bleeding without treatment. Patients lack a gene needed to help the blood clot.