A Study of Fitusiran in Severe Hemophilia A and B Patients Previously Receiving Factor or Bypassing Agent Prophylaxis

Inclusion Criteria

• •Males, \>=12 years of age.
• •Severe hemophilia A or B (as evidenced by a central laboratory measurement at screening or documented medical record evidence of FVIII less than (\<) 1 percent (%) or FIX level less than or equal to (\<=) 2%).
• •A minimum of 2 bleeding episodes required BPA treatment within the last 6 months prior to screening for participants with inhibitory antibodies to factor VIII or factor IX (Cohort A). A minimum of 1 bleeding episode required factor treatment within the last 12 months prior to screening for participants without inhibitory antibodies to factor VIII or factor IX (Cohort B).
• •Met either the definition of inhibitor or non-inhibitor participant as below:
• •Inhibitor: Use of BPAs for prophylaxis and for any bleeding episodes for at least the last 6 months prior to screening, and met one of the following Nijmegen-modified Bethesda assay results criteria:
• •Inhibitor titer of \>=0.6 Bethesda Unit per milliliter (BU/mL) at screening, or
• •Inhibitor titer of \<0.6 BU/mL at screening with medical record evidence of 2 consecutive titers \>=0.6 BU/mL, or
• •Inhibitor titer of \<0.6 BU/mL at screening with medical record evidence of anamnestic response
• •The subgroup of participants in Cohort A participants might additionally meet the following criteria to be eligible to start treatment with fitusiran directly after the screening period:
• •* Hemophilia B with inhibitory antibody to Factor IX as defined above
• •* Not responding adequately to BPA treatment (historical ABR \>=20) prior to enrollment
• •* In the opinion of the Investigator, with approval of Sponsor Medical Monitor, 6-month BPA prophylaxis period should be omitted.
• •Non-inhibitor: Use of factor concentrates for prophylaxis and for any bleeding episodes for at least the last 6 months prior to screening, and met each of the following criterion:
• •Nijmegen-modified Bethesda assay inhibitor titer of \<0.6 BU/mL at screening and
• •No use of BPAs to treat bleeding episodes for at least the last 6 months prior to screening and
• •No history of immune tolerance induction therapy within the past 3 years prior to screening.
• •Documented prophylactic treatment with factor concentrates or BPAs for the treatment of hemophilia A or B for at least 6 months prior to screening.
• •Adherent to the prescribed prophylactic therapy for at least 6 months prior to screening per Investigator assessment.
• •Willed and complied with the study requirements and to provide written informed consent and assent.