The FDA has agreed to allow Alnylam (NASDAQ: ALNY) and Sanofi (NYSE: SNY) to resume trials of their hemophilia therapy, fitusiran. Previously, these companies had to halt their fitusiran studies after a patient who had advanced into an extension study died because of a fatal blood clot. Is this news good for patients and investors?Hemophilia A is caused by a deficiency of blood coagulation factor VIII and hemophilia B is caused by a deficiency of blood coagulation factor IX.