A Study to Test a Medicine (Fitusiran) Injected Under the Skin for Preventing Bleeding Episodes in Male Adolescent or Adult Participants With Severe Hemophilia

Inclusion Criteria:

• Diagnosis of severe congenital hemophilia A or B (FVIII <1% or FIX level ≤2%) asevidenced by a central laboratory measurement at screening or documented medicalrecord evidence.

• For participants currently not on prophylaxis (CFC or BPA on-demand): A minimum of 4bleeding episodes requiring BPA (inhibitor participants) or CFC (non-inhibitorparticipants) treatment within the last 6 months prior to screening.

• Willing and able to comply with the study requirements and to provide writteninformed consent and assent in the case of participants under the age of legalconsent, per local and national requirements

Exclusion Criteria:

• Known co-existing bleeding disorders other than congenital hemophilia A or B

• History of arterial or venous thromboembolism, not associated with an indwellingvenous access

• History of intolerance to SC injection(s).

• Current participation in immune tolerance induction therapy (ITI)

• Prior gene therapy

• Current or prior participation in a fitusiran trial

• Current or prior participation in a gene therapy trial

• Received an investigational drug or device within 30 days prior to the screeningvisit or within 5 half-lives of the investigational drug (or device) prior to thescreening visit, whichever is longer

• Presence of clinically significant liver disease AT activity <60% at Screening

• Co-existing thrombophilic disorder

• Hepatitis C virus antibody positive, except participants who have negative HepatitisC viral load and no evidence of cirrhosis

• Presence of acute hepatitis, ie, hepatitis A, hepatitis E.

• Presence of acute or chronic hepatitis B infection

• Known to be HIV positive with CD4 count <200 cells/μL.

• Reduced renal function The above information is not intended to contain allconsiderations relevant to a patient's potential participation in a clinical trial.