A Study to Describe Patient REal-world FitusiRan ExpeRience

This is a real-world, mixed-methods observational study conducted among adolescent (ages 12-17 years) and adult participants diagnosed with hemophilia A or B, with or without Factor VIII (FVIII) or Factor IX (FIX) inhibitors, who are treated with fitusiran. The study includes a prospective longitudinal cohort (Cohort 1) and a cross-sectional cohort (Cohort 2). Data collection includes patient-reported outcomes via online surveys, qualitative interviews conducted via teleconference, and electronic medical record (EMR) review to describe real-world patient experiences, treatment satisfaction, adherence, and clinical management of fitusiran.

Inclusion Criteria: * Participant is English speaking * Participant is ≥ 12 years of age at the time of consent \-- Signed written informed consent by participants who are legally adults (i.e., have reached the age of majority as defined by local law) or legally authorized representative (e.g., parent) and assent (for participants under the age of majority by local law) * Participant has a diagnosis of hemophilia A or B * Participant is using fitusiran (QFITLIA) for: * Prospective cohort: \< 6 months at the time of consent * Cross-sectional cohort: 9-15 months at the time of consent * Participant has access to an internet-connected computer or mobile device * Participant is willing and able to participate in: * Prospective cohort: Up to three 30-minute online surveys and two 60 minute virtual interviews over an approximately 12-month period * Cross-sectional cohort: A 30-minute online survey and 60-minute virtual interview * Participant resides in the US Exclusion Criteria: * Prospective cohort: Participated in a clinical trial for fitusiran * Cross-sectional cohort: Participated in the prospective cohort The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.