The main purposes of this study are to determine if use of emicizumab prophylaxis treatment reduces number of bleeding episodes, if it improves quality of life of individuals and if improves arthropathy in persons with hemophilia A.

The main purpose of this study is to determine if use of emicizumab prophylaxis treatment reduces number of bleeding episodes and if it affects quality of life of individuals with hemophilia.

Patients with hemophilia A, especially those with severe disease, have recurrent bleeding in joints, muscles and deep tissue and recurrent bleeding in the same joint can result in irreversible damage in bone and cartilage and lead to disabling arthropathy. Treatment involves replacement with exogenous recombinant factor concentrates that can prevent further bleeding episodes but not the ongoing joint damage. In addition, treatment with recombinant factor concentrates can lead to inhibitory antibodies resulting in inability to use those for further treatment. The burden of this disease on patients and caregivers is well recognized.

Participant will be asked about bleeding episodes needing additional factor replacement in addition to checking bleeding log prior to starting emicizumab and at additional times after starting emicizumab. In addition, investigators would ask participant to complete questionnaire about participant's and/or their caregiver's quality of life prior to starting emicizumab and at additional times after starting emicizumab. Participant will also have joint scores measured before and at additional times after starting emicizumab. All the information collected will remain confidential and would only be shared with members of study team.

Inclusion Criteria Part A: ABR

• Signed Informed Consent/Assent Form
• Age 4 years at time of signing Informed Consent Form
• Ability to comply with the study protocol, in the investigator's judgment
• Diagnosis of hemophilia A (any severity) on emicizumab or factor concentrate prophylaxis for at least 12 months each
• Plan to be adherent to emicizumab prophylaxis during the study
• Patient with inhibitors
• Patient without inhibitors Part B: HRQoL and Arthropathy
• Signed Informed Consent/Assent Form
• Age 4 years at time of signing Informed Consent Form
• Ability to comply with the study protocol, in the investigator's judgment
• Diagnosis of hemophilia A (any severity) who has decided to switch to emicizumab prophylaxis
• Plan to be adherent to emicizumab prophylaxis during the study
• Individuals of childbearing age will be included in this study. Their participation involves voluntary completion of a questionnaire. There are no additional precautions required for this population.
• Patient/parent must be able to read and write English/Spanish

Exclusion Criteria:

• Part A: ABR

  • Patients who are on a clinical trial for prophylaxis
  • Patients with other bleeding disorders needing any scheduled treatment
  • No eligibility restrictions will be based on gender, race, ethnic background or economic status

Part B: HRQoL and Arthropathy

• Patients who are on a clinical trial for prophylaxis
• Patients with other bleeding disorders needing any scheduled treatment
• Patients/parents who refuse to complete questionnaire or have joint health assessment by HJHS
• No eligibility restrictions will be based on gender, race, ethnic background or economic status

The study population will include children and adults who are males and females with hemophilia A for all parts of the study. Children and adults are equally at risk for bleeding and hence we would collect information about bleeding events in both children and adults on emicizumab or on factor concentrates to calculate ABR. There will be no exclusion based on race or ethnicity. For HRQoL part of the study, children and their families will be included.The Quality of life was found to be poor both among children affected with hemophilia and their parents and perceived impact on family. Hemophilic arthropathy can be seen in children and adults and therefore, this outcome must be studied in both populations as it can be disabling at any age.