Both types are the result of mutations that cause people to produce less of a specific clotting factor, which are proteins vital for forming blood clots; hemophilia B is characterized by a deficiency of Factor IX.Because the genes involved in hemophilia are found on the X chromosome, most people who experience symptoms are men, while most affected women can carry a mutated gene without illness.On Wednesday, the FDA announced the approval of Hemgenix for the treatment of hemophilia B in people with a current or past history of severe bleeding episodes or who are taking Factor IX prophylaxis therapy.In two small trials of patients with moderate to severe hemophilia B, the therapy seemed to just do that, raising people’s measured levels of Factor IX.The company argues that the drug will likely still be less costly over the long run than the current standard of care since it should reduce the frequency of expensive transfusions; they also say that the drug’s effectiveness is expected to last for several years at least."